QT5/f Digitized by the Internet Archive in 2010 with funding from Open Knowledge Commons http://www.archive.org/details/manualofpracticaOOexmo %i^? *>.A ^ A A.. , .ii %. MANUAL OF PRACTICAL MEDICAL AND PHYSIOLOGICAL CHEMISTRY BY £ CHARLES E. PELLEW, E. M. DEMONSTRATOR OF PHYSICS AND CHEMISTRY IN THE COLLEGE OF PHYSICIANS AND SURGEONS (medical DEPARTMENT OF COLUMBIA COLLEGE), NEW YORK HONORARY ASSISTANT IN CHEMISTRY AT THE SCHOOL OF MINES, COLUMBIA COLLEGE, ETC. IVITH ILLUSTRATIONS NEW YORK D. APPLETON AND COMPANY 1892 ■f-^u li,. nil' /I, COPTEIGHT, 1892, By CHARLES E. PELLEW. PEEFACE During the suiiiuier of 1887, the author, who had been recently appointed to take charge of the new chemical laboratory at the College of Physicians and Surgeons, in company with Prof. C. F. Chandler, visited or interrogated most of the leading medical col- leges both in this country and abroad, with a view to determine the course of practical chemical instruction to be adopted for the coming term. It was found that in every case where the practical instruction given was more than merely urine analysis, with sometimes a little toxicology, it consisted of a regular course of qualitative, and perhai^s some quantitative, analysis. This method it was decided not to adopt. There seemed to be too much pure chemistry and too little medicine in such a course for students who were studying to be physicians, and not chem- ists. So, with the advice and assistance of Dr. Chandler, a course was prepared, limited, by the size of the laboratory and the length of the term, to thirty lessons, in which, as far as possible, every subject and every test had some bearing upon the studeiit's other work. The lessons for this course of laboratory work were published in pamphlet form in 1889, and the present book contains the same lessons revised, and amplified with a descriptive and ex- planatory text. It will be noticed that these lessons not only deal with true physiological chemistry, with the foodstuffs and their pi'oducts of assimilation, and with the different fluids and tissues of the body, but that, wherever possible, particular attention has been paid to the latest clinical tests. Special care has been bestowed on the tests of breast milk, for which the author wishes to thank Dr. L. Ennnett Holt, and on those of the gastric juice, largely taken from the excellent paper of Dr. F. P. Kinnicutt. IV PPvEFACE. Some of the illustrations will, it is hoped, prove of interest. The drawings of crystals, in the fii'st half of the book, were in- serted mainly with the idea of accustoming the student to the free use of the microscope. It will be noticed, however, that most of these crystals also occur among the diiferent urinary deposits described in the last part. Attention is called to the microphotographs of blood-cells. Plates IV. and V., inserted by the courtesy of Dr. John S. Billings, U.S.A., which illustrate the extreme difficulty, if not the impossibility, of distinguishing between human blood and that of some other mammalia. Spe- cial thanks are due to Dr. E. G. Love for his fine drawings of starch granules. Figs. 1 and 2 ; to Dr. H. Holbrook Curtis for the use of Plates VII. and VIII., taken from his translation of Hoff- mann and Ultzmann's " Urine Analysis ; " and to Messrs. Appleton & Co. for the loan of several cuts from Prey's " Histology " and Flint's " Physiology." Besides gratefully acknowledging his indebtedness to Dr. Chandler, the author wishes to return his hearty thanks to Dr. John Gf. Curtis, Dr. T. M. Prudden, and Dr. William G. Thomp- son for their kind assistance in looking over and ci-iticising the proof-sheets ; and also to his many friends on the former and pres- ent House Staffs of the hospitals in this city, who have never, from the first year of the laboratory, failed to assist him in every possible way with both material and information. College Physicians and Suegeons, August 36th, 1898. COXTEISTTS. PART I. CARBOHYDRATES. PAGE Introductiox 3 LESSON I. Cellulose axd Starch. Cellulose, 6 Starch, 8 Laboratory Experiments on Cellulose and Starch, . . 10 LESSON II. Dextrin, Glycogex, and Glucose. The Dextrins, 13 Glycogen, U Dextro-Glucose or Dextrose, 16 Lsevulose, 18 Galactose, 18 Laboratory Experiments on Dextrin and Glucose, . , 24 LESSON III. Conversion of Starch into Dextrin, Glucose, and Mal- tose. Fermentation. The Conversion of Starch into Dextrin, Glucose, and Mal- tose 27 Fermentation, . 29 Bodies acting like Ferments, 29 Unorganized Ferments, 30 Organized Ferments, 33 Laboratory Experiments on Conversion of Starch into Dex- trin, Maltose, and Glucose, 34 VI CONTENTS. LESSON IV. Cane Sugar, Milk Sugar, ais^d Fermentation. Di-Sac- charoids or saccharoses. PAGE Cane Sugar, 36 Milk Sugar or Lactose, 38 Malt Sugar or Maltose, 40 Fermentation Experiment, 40 Laboratory Experiments on Cane Sugar, Milk Sugar, and Fermentation, 41 LESSON V. Alcohol, Carbon Dioxide, and Yeast. Alcohol ; Ethyl Alcohol 43 Laboratory Experiments on Alcohol, Carbon Dioxide, and Yeast, 4G PART 11. THE FATS AND FIXED OILS. LESSON VL Fats and Soaps. The Fats and Fixed Oils, 51 Soap, 54 Laboratory Experiments on Fats and Soaps, . . . 5G LESSON VIL Butter, Oleomargin, Glycerin, and Oils. Butter, 59 Glycerin, 61 The Oils, 63 Laboratory Experiments on Butter, Oleomargarin, Gly- cerin, and Oils, 56 PART III. THE PROTEIDS OF ALBUMINOUS BODIES. Introduction, 69 Animal Proteids, 73 VegetaV>le Proteids, TS Albuminoids, '^'^ CONTENTS. Vll LESSON VIII. The General Proteid Reactioxs. VlTELLIN. The Albumixs and The General Protoul Reactions, Animal Proteids The Albumins, .... Globulins, Vitellin, Laboratory Experiments, The General Proteid Reactions, Egg and Serum Albumins, etc., LESSON IX. PAGE 74 7(5 70 7!) 80 81 Crystallin, Myosin, Ac ID AND . Alkali Albumins. Crystallin, 84 Myosin, .... 84 Paraglobulin, 85 Fibrinogen, .... 85 Acid Albumins, . 86 Syntonin, .... 87 Alkali Albumins, 87 Laboratory Experiments on Crystallin, Myosin, Acid and Alkali Albumins, 88 LESS 30N X. Fibrin, Coagulated Proteids, Lardacein— The Vege- table Proteids— Tests for Sulphur in Proteids. Fibrin, 90 Coagulated Proteid.s, 91 Amyloid Substance — L^i'thi^t'ein, 91 Vegetable Proteids, 92 Sulphur in Proteids, 95 Laboratory Experiments on Syntonin, Coagulated Proteids, Gluten, Tests for Sulphur in Proteids, .... 97 PxiRT IV. THE INORGANIC CONSTITUENTS OF THE BODY. LESSON XI. Oxygen, Hydrogen, Chlorine, and Hydrochloric Acid. Oxygen 10.3 Hydrogen, 104 VUl CONTENTS. PAGE Chlorine 106 Hydrochloric Acid, 108 Laboratorj^ Experiments on Oxygen, Hydrogen, Chlor- ine, and Hydrochloric Acid, 110 LESSQ]^ XII. Sulphuric, CARBOific, and Nitric Acids. Sulphuric Acid, 114 Carbonic Acid, 116 Nitric Acid, 118 Laboratory Exioeriments on Sulphuric, Carbonic, and Nitric Acids, 120 LESSON XIII. Phosphoric Acids, Iron, and Aluminium. (Ortho-)Phosphoric Acid, 124 Iron, 125 Aluminium, 127 Laboratory Experiments on Phosphoric Acid, Iron (Ferrous and Ferric), and Aluminium, 130 LESSON XIV. Calcium and Magnesium. Calcium, 133 Magnesium, 135 Laboratory Experiments on Calcium and Magnesium, . . 136 LESSON XV. The Alkaline Metals (Ammonium, Sodium, Potassium, and Lithium), Wood Ashes, Acidimetry and Alkalimetry. The Alkaline Metals, 138 Ammonium, 138 Sodium, 139 Potassium, 140 Lithium 140 Wood Ashes, 141 Acidimetry and Alkalimetry, 141 Laboratory ExiJeriments on the Alkaline Metals, Wood Ashes, Acidimetry and Alkalimetry, 142 CONTENTS. IX PAET V. WATER ANALYSIS. LESSON XVI. PAGE Water for Manufacturing Purposes, 147 Water for Laundry Purposes, 148 Biological Tests, 149 Chemical Tests 151 Analysis of Croton Water, 156 Mineral Waters, 157 Laboratory Experiments on Water Analysis, . . . 158 PAET VI. ANIMAL TISSUES AND SECRETIONS. LESSON xvn. Bone 165 Laboratory Experiments on Bone, 169 LESSON xvin. Milk. General Properties 172 Cow's Milk, 173 Human Milk, 173 The Testing of Milk 178 Koumyss, 183 Laboratory Experiments on Milk and Koumyss, . . . 184 LESSON XIX. Blood. Genei'al Properties, Composition, etc., 187 Laboratory Experiments on Blood, . ... . . 194 LESSON XX. Blood (Continued) and Bilk. Blood Stains, 197 The Bile, 201 Constituents of Bile, 202 Lecithin, 204 Bile Pigments, 204 X CONTENTS. PAGE Mucin 206 The Bile Salts, 206 Glycogen, 207 Laboratory Experiments for Blood (Continued) and Bile, . 208 PART yii. THE DIGESTION. LESSON XXI. General Principles of Digestion, 213 Diffusion of Fluids, 213 The Saliva 216 Gastric Juice, 217 Clinical Tests on the Gastric Juice, 220 The Pancreatic Juice, 234 Laboratory Experiments on Gastric, Pancreatic, and Sali- vary Digestion, 227 PART VIII. THE URINE. Introduction, - - • 235 LESSON XXII. General Properties of Urine. General Physical Properties, 238 General Chemical Properties, 243 Laboratory Experiments on the General Physical and Chemical Properties of Urine, 244 LESSON XXIII. Urea and Uric Acid. Urea, 246 Uric Acid 250 Laboratory Experiments on Urea and Uric Acid, . . 253 CONTENTS. XI LESSON XXIV. Albumin in Urine. PAGE Description, 255 Laboratory Experiments on Albumin in Urine, . . . 257 LESSON XXV. Glucose in Urine. Description, 259 Laboratory Experiments for Glucose in Urine, . . . 262 PART IX. MICROSCOPICAL EXAMINATION OF THE URINE. Introduction, 2G7 LESSON XXVI. Sediments in Acid Urine. Uric-Acid Crystals, 269 Acid-Urates, 270 Calcium-Oxalate Crystals, 270 Hippuric-Acid Crystals, 271 Calcium-Sulphate Crystals, 271 LESSON XXVII. Sediments in Alkaline Urine. Triple-Phosphate Crystals, 272 Calcium-Phosphate Crystals, 273 Calcium-Carbonate Crystals, 273 Leucin and Tyrosin Crystals, 273 Cystin Crystals, , . . 274 LESSON XXVIII. Casts, 275 LESSON XXIX. Red Blood-Cells, 279 Pus Cells, 280 Epithelial Cells, 282 xii CONTENTS. LESSON XXX. PAGE Spermatozoa, 284 Microbes, 384 Foreign Bodies, 285 APPENDIX A. Table of Weights and Measures, 287 APPENDIX B. Alphabetical Table of Equivalent Values of Weights and Measures, 388 APPENDIX C. Table of Atomic Weights, . . . . . . . .389 APPENDIX D. List of Reagent Bottles and Their Contents, .... 290 APPENDIX E. List of Apparatus, 292 APPENDIX F. List of Extra Apparatus, Chemicals, etc., Required for the Different Lessons of the Course, . . . . . . 294 Index, 309 LIST or ILLUSTRATIOXS. Via. PAGE 1. Potato starch Dr. E. G. Love 12 2. Corn Starch Dr. E. G. Love 12 3. Fermentation Apparatus C. E. P 42 4. Distilhng Apparatus C. E. P 48 5. Colostrum (human) Funke 172 G. Milk Corpuscles (human) Funke 173 7. Lactometer, N. Y. Board of Health. . . .Dr. Chandler 179 8. Hjemin Crystals; X 250 C. E. P 208 9. Cholesterin Crystals Frey 209 10. Epithelial Cells of Mouth Frey 21G 11. Leucin Crystals Funke 226 12. Tyrosin Crystals I unke 226 13. Uriniferous Tubules Frey 236 14. Glomerules from Rabbit Frey 237 15. Doremus' Urea Apparatus C. E. P 252 16. Marshall's Urea Apparatus C. E. P 252 17. Centrifugal Separator for Urine Sediments.. C. E. P 207 18. Calcium-Oxalate Crystals ; x 300 C. E. P 271 19. Calcium-Phosphate Crystals ; X 130 C. E. P 273 20. Cystin Crystals Frey 274 21. Hyahne and Waxy Casts C. E. P 276 22. Granular Casts C. E. P 277 23. Red Blood Corpuscles (human) Sternberg 279 24. Pus Cells C. E. P 280 25. Gonorrhceal Thread, with Spermatozoa . . . .C. E. P 282 26. Epithelial Cells C. E. P 283 27. Human Spermatozoa Frey 284 28. Fibres: Wool, Cotton, and Linen C. E. P 285 xiv LIST OP ILLUSTRATIONS. PLATE I. (C. E. P.) Fig. 1. Phenyl Glucosazon. Fig. 2. Phenyl Glucosazon. Fig. 3. Iodoform. Fig. 4. Mould. Fig. 5. Yeast. Fig. C. Bacteria. PLATE II. (C. E. P.) Fig. 1. Ammonia-Phospho-Molybdate. Fig. 2. Triple Phosphate, rapid precipitation. Fig. 3. Alum, evaporated. Fig. 4. Alum, precipitated. Fig. 5. Calcium Carbonate, formed by the breath. Fig. G. Calcium Sulphate. PLATE III. (C. E. P.) Fig. 1. Calcium Oxalate. Fig. 2. Triple Phosphate, rapid precipitation. Fig. 3. Triple Phosphate, same specimen after standing 24 hours. Fig. 4. Sodium Chloride. Fig. 5. Sodium Antimonate. Fig. C. Potassium (or Ammonium) Platinic Chloride. PLATE IV. (Dr. Woodward.) Human Blood. Dog's Blood. PLATE Y. (Dr. Woodward.) Human Blood, dried. Frog's Blood. PLATE YI. (C. E. P.) Fig. 1. Urea. Fig. 2, Urea Nitrate. Fig. 3. Urea Oxalate. Fig. 4. Urea Sodium Chloride. Fig. 5. Uric Acid, from snake's excrement. Fig. 6. Uric Acid, from acidified urine. PLATE VII. (Hoffmann and Ultzmann.) A. Uric Acid. B. Acid Fermentation. PLATE VIII. (Hoffmann and Ultzmann.) A. Triple Phosphate. Calcium Phosphate. B. Alkaline Fermentation. PART I. THE CARBOHYDRATES. THE CARBOHYDRATES. INTRODUCTION. Occurrence. — The name Carbohydrate has been given to a very important series of Proximate Principles, found chiefly in the vegetable kingdom, where they compose by far the greater bulk of the plant tissue, but also found in smaller quantities in the animal kingdom. Composition, — The carbohydrates contain no nitrogen — only carbon, hydrogen, and oxygen. As the name signifies, the last two are in the proportion to form water. There are, however, many substances of a similar comijosition, CmHonOn, such as acetic acid, C2H1O2, lactic acid, CsHeOa, pyrogallic acid, CsHsOa, and others, which have nothing else in counuon with this group. In order to belong to the carbohydrates, a substance must satisfy the following conditions : 1st. It must contain at least six atoms of carbon and, in gen- eral, five atoms of oxygen. 2d. It must be composed of carbon, hydrogen, and oxygen, only, with two atoms of hydrogen for every one of oxygen. 3d. Either unchanged, or after treatment with various re- agents, such as heat, acids, ferments, etc., it must have at least some of the following properties : (a) A sweet taste. ib) The power to rotate a beam of polarized light. (c) The power to reduce solutions of certain metals, such as copper, bismuth, mercury, etc. (d) The property of undergoing alcoholic fermentation. General Properties. — The carbohydrates are, almost without exception, neutral in reaction. They form some loose chemical combinations with other substances, principally bases, a fact which is sometimes used as a means of purifying them. 2 4 MEDICAL CHEMISTRY. Many of them crystallize readily, like cane and milk sugar and dextrose ; others can be crystallized, but only with great diflfi- culty. Still others of the series, like starch and cellulose, are distinctly colloid in both appearance and properties. These latter are of a more complex structure than the former. Their exact chemical composition is at present but little known. Classification. — Carbohydrates can be classified according to their composition, dividing them with reference to the number of times that they contain a group of six carbon atoms. On this basis the following table can be made : I. MOXO-SACCHARIDS, or GtLUCOSES.— CeHriOe. Dextro-gluGose (dextrose, grape sugar). Zcevo-glucose (Isevulose). Galactose. /Sorbose, and others, of less importance. II. Di-Saccharids, or Saccharoses.— Ci^HoaOii. Sucrose (saccharose, cane sugar). Lactose (milk sugar). Maltose (malt sugar) and others. III. POLT-SACCHARIDS.— u(C6Hio05) ± mCHsO). 1st. Crystallizing. Rafflnose, lactosin, and others, all of little iniportance. 2d. Colloid. Cellulose. Starch, dextrins, and other derivatives, all polarizing to the right. Inulin, and its derivatives, polarizing to the left. Glycogen. Arabinose, gums, etc. In general it may be said that the last group, of poly-saccharids, is by far the most complex in character. Its members may be readily broken down into simpler carbohydrates by a variety of reagents, while, so far, with but few exceptions, we have been unable to build them up without the agency of plant life. The second group, of di-saecharids, although simi)]er than the last, and in some cases made from them, are still far more THE CARBOHYDRATES. 5 complex than the glucoses, into which they can be readily broken down ; while any attempt to break down the latter into still simpler compounds only results in destroying their composition, and decomposing them into substances no longer to be considered carbohydrates. LESSO]^ I. CELLULOSE AND STARCH. CELLULOSE,— (CeHioOs).!. Occurrence. — Cellulose is present in all the tissues of the higher plants, and in most of the lower forms of vegetable life. It may be considered as the framework, the skeleton, of these plants. In the more delicate tissues it is found i:)erfectly pure, forming the walls of the minute cells, which act as the basis for all parts of the structure. This is well seen under the microscope in studying the potato section, where the round and oval starch grains lie inside the delicate threads of cellulose which define the cells. In the solid portions of the plant Avhich we call wood the cellulose, still form- ing the framework, is fiime:" in structure, and more or less con- taminated with thickening and stiffening materials, both organic and inorganic. It is worth noticing, however, that even in those parts of the plant like the trunks of trees, which have to stand the greatest stress, the percentage of mineral matter rarely runs over 6 or 7%, while in the bones of animals about two-thirds of their weight is mineral matter. The cellulose is probably formed in the plants from the various carbohydrates, such as cane sugar, dextrin, and glucose, dissolved in the sap. Preparation. — Cellulose is prepared in a pure state from almost any vegetable tissue by simply reducing it to a pulp and then Avashing away the various impurities, starch, gums, fats, and salts, which maybe x^resent. In our experiment the grating process breaks up the cells and sets the starch granules free. Then, by washing and straining, the threads of cellulose which formed the cell walls are finally left in a more or less pure condition. Cellulose is thus i)repared from wood, flax, cotton, hemp, and other similar materials, on a large scale, and comes into commerce in the form of paper, linen, cotton, cordage, etc. The finer vari- CELLULOSE. 7 eties of filter paper and of absorbent cotton are, excepting for the moisture they contain, ahuost chemically pure cellulose. Composition. — Cellulose is composed of 44.o;j carbon, (>% hydro- gen, and 4d.5% oxygen. Its exact chemical formula is not known, but it is some multiple of the formula CeHioOa. Properties. — In a pure state it consists of extremely fine, colorless, flexible, slightly elastic fibre.s, which mat together to form the paper and cotton, with which we are familiar. These fibres are doubly refracting, often giving a play of colors when seen by polarized light. When perfectly pure, cellulose is quite unaltered by either air or moisture. As we find it in nature, however, it is invariably associated with more or less other organic matter, carbohydrates, proteid.s, etc., and then it gradually undergoes decomposition by the aid of the lower organisms. It is insoluble in water, and is affected but little by most of the ordinary reagents. Strong alkalies, like caustic potash or soda, soften it and alter its structure more or less, without, however, actually dissolving it. Strong acids also affect it to some extent, and concentrated sul- phuric acid decomposes it completelj', even in the cold, breaking it down into dextrin and glucose, and some dark-colored deriva- tives, belonging to the caramel group. When as paper, it is exposed to the action of sulphuric acid only for a moment, a curious change takes place ; part of the cel- Itilose is changed to hydro-cellulose, a jelly-like substance, which settles between the fibres of the jxiper and thus forms the so-called "Parchment Paper," v. Lesson XI. This hydro-cellulose, or amy- loid as it is sometimes called, is colored blue by iodine. Cellulose is completely dissolved by a strong solution of cupric hydrate in amnionic hydrate, from which it is rei)recipitated by neutrahzing with strong acid, or even by diluting greatly with water. It is also soluble in an acid solution of zinc chloride. Excepting, possibly, in some of the most delicate tissues, e.y., in young vegetables, cellulose is but little afifected by the human digestive ferments. Herbivorous animals, however, are able to digest it in certain forms without much difficulty. Uses.— It is used enormously in the arts, either in a com- paratively pure condition, as cotton, linen, rope, and jiaper, or 8 MEDICAL CHEMISTRY. mixed \yith other materials, as papier mach6 and similar pro- ducts, or in the form of wood. It also serves as a basis for the manufacture of certain nitro-compounds, such as nitro-cellulose or gun-cotton, and of their derivatives, celluloid, lignoid, and the like. STARCH.— (CeHioOsK Occurrence. — Starch is found in small quantities in the leaves, bark, stem, and in fact almost every organ of the higher plants. It occurs in much greater abundance in the seeds, roots, and tubers, Avhere it is stored up as food for the young plant. In a natural condition potatoes contain about 20^ of dry starch and nearly 70% of water ; in wheat, corn, and other cereals the per- centage of stai'ch varies from 50^-70;^, according to their quality and dryness. It is generally considered that starch is formed, directly or in- directly, in the leaves of all green plants by sunlight, acting through chlorophyll on water and the carbon dioxide of the at- mosphere. Oxygen is liberated at the same time, perhaps ac- cording to the imperfect formula GCOa+SHoOrrrCeHioOs+CO^. Preparation. — Starch is prepared from either potatoes or grain, by a process similar in everj^ respect to that in the lesson. It always occurs in the form of minute microscopical particles, filling more or less completely the cell wall of cellulose. To ex- tract the starch it is sim^ily necessary to break up these cells by crushing or grating, after which the starch granules can be washed out, strained from the coarser fibres of cellulose and from other d(5bris, and finally washed by decantation or other- wise. To obtain a very pure product this washing is conducted with great care, and with the addition of a little soda to dissolve off tlie last traces of joroteid and fatty material. Composition. — Commercial starch always contains some water, as well as faint traces of salts, albumin, fat, etc. When pure its composition is the same, so far as wc can tell, as that of cellulose, and we give it the same indefinite formula of (CoH,oOo)n. Properties. — The granules of every variety of stai'cli, Avhile differing from each other in size (0.003 to 0.1 millini.), in shape, STARCH. 9 and in appearance, still possess the same general structure. They seeiu to be composed of layers, overlapping one another, and covering in a central portion. The generally received theory is that two entirely different substances enter into the composition of these granules. The one, insoluble starch or starch cellulose, comprises the outer layer of thin husks, impermeable to cold water, and shielding the far larger amount (over 95% of the whole), of the more valuable soluble starch or starch granulose within. Hence it is that the starch grains are quite insoluble in cold water, but when treated with hot water or with alkalies the layers of starch cellulose are loosened and finally peel off, scatter- ing through and thickening the licjuid, and exposing the soluble granulose within. Hot dilute acids and also the more powerful ferments, like diastase and amylopsin, are able to penetrate the outer covering and to disintegrate and change to maltose the raw starch. This occurs in nature, when the seeds that have lain in the ground all winter begin to germinate in the spring, and the diastase ferment, then formed, digests the stored-up starch, and thus nourishes the young plant till it can take care of itself. The action, however, even of the diastase, is far more rapid if the starch grains have been first disintegrated by boiling. An important property of starch is the facility with which various agents — heat, acids, ferments, etc. — break it down into dextrin, and into maltose, or glucose. This is a necessary part of the process of digestion, for starch as such is a " colloid" or non- dialyzing substance, and befoi'e it can be assimifated must be changed to a "crystalloid" body like the two last mentioned. In the human body this is done to a slight extent by the saliva, but principally by the amylopsin ferment of the pancreatic juice. Tests.— The principal test for starch is the formation of a blue compound known as iodide of starch, whenever free iodine is allowed to act on starch granulose. The cellulose layers in raw starch do not change color themselves, but allow the iodine to penetrate through them. It is probable that this substance is a pm-e chemical com- pound of iodine with the starch molecule, and that the presence of some hydriodic acid is necessary for its produc- 10 MEDICAL CHEMISTRY. tion. It is purplish blue when wet, and brown when dry ; it contains, when pure, about 18^ of iodine. It is not a stable compound. Heat is sufficient to decompose it into starch and free iodine, and if the heat is continued long enough all the iodine is driven oflf. Otherwise the color returns on cooling. The iodine is also removed from the compound by caustic potash, argentic nitrate, mercuric chloride, and in fact, any chemical for which it has a strong affinity. Uses. — The principal use of starch is, of course, for food. It serves also as a raw material in the manufacture of alcohol, and is prepared pui'e on an enormous scale, partly for food, partly for stiffening linen, papei", etc., and also for the preparation of dextro- glucose and dextrin. LABORATORY EXPERIMENTS. CELLULOSE AND STARCH. I. Preparation of Starch and Cellulose from Potato. — Grate a potato to a pulp with the tin grater on to the agateware plate. Wash the pulp through a strainer into the agate cup Avith water from the wash bottle, working it thoroughly at the same time with the fingers. Continue this until the water no longer rvins through milky. Put the washed pulp aside on filter paper = Cellulose, loith some starch. Decant off the w^ater in tlie cup, carefully saving the whitish sediment in the bottom. Fill the cup again with water, let it settle a few minvites, and decant again Avith care. Then scrape the Avhite residue on to a piece of filter paper = Starch. II. Microscopic Examination. — Examine with both high and low powers a thin section of potato. Notice how the starch granules lie inside the cells whose Avails are of cellulose. Then add a drop of iodine solution diluted three or four times Avith A\'ater, and examine again. Notice, the blue starch granules. Examine, both with and without iodine, some of the prepared starch and some corn starch, mixing a very little of each with a drop of water and spreading it Avell out on the slide. Notice the CELLULOSE AND STARCH. 11 "oyster-shell" markings of the potato starch, and the star- shaped " hilum " of the corn starch. III. Chemical Tests.— 1st. Fill a test-tube half full of potassie hydrate (KOH), and add a little starch in powder. The starch swells and forms a paste in the cold. 2d. Fill the agate saucepan half full of water, place it on a tripod, and boil it vigorously with a Bunsen burner. Put about a tablespoonful of starch into a mortal*, and grind it and mix it with enough water to form a smooth thin milk. Add this milk to the water as it boils. Notice that the white color at once disappears and it forms starcJi paste. Pour some of this paste into a beaker and add a few droi)S of iodine solution = deep blue. Put this blue paste into four differ- ent test-tubes and test as follows : (a) Heat the 1st gently over the flame ; the color finally disap- pears completely. Then let it cool. If the paste was heated till the iodine volatilized, no color will reappear, but if carefully managed the blue color will return when the paste cools. (&) To the 2d add a little KOH ; the color disappears. Then add a little dilute hydrochloric acid (HCl dil) ; the color returns. (c) To the 3d add a few drops of argentic nitrate (AgNOa) ; the color disappears. (fZ) To the 4th add some mercuric chloride (HgCli) ; the color disappears. 3d. Put a little paste in a beaker; add plenty of water, stir, and filter the mixture into a test-tube. To this clear filtrate add a few drops of iodine = blue, just like the unfiltered paste. IV. Cellulose. — Examine under the microscope, both with and without iodine, some cellulose from I., and also a few shreds of filter paper, thoroughly wet with water. Notice that the iodine hardly stains the cellulose at all, while it turns blue any grains of starch that may be present. If you have the time, examine some filter paper and grains of starch under the microscope, with the aid of polarized light. Place a few shreds of filter paper, wet with water, in three different test-tubes, and test as follows: {a) To the 1st add some water and boil ; this has no effect. 12 MEDICAL CHEMISTRY. (b) To the 2d add some KOH ; the fibres swell slightly, and, after a time, become more or less gelatinous. (c) To the 3d add a few drops of common sulphuric acid* (HoSOj); the cellulose turns brown or black and quickly dissolves. (d) Put some cellulose from I., and some filter paper, into sep- arate test-tubes, and add to each an inch or so of the Cupric Hydrate solution. Shake, w^arm gently, and notice that the cellulose dissolves completely. Put this solution of cellulose in a small beaker and add some dilute hydrochloric acid, stirring it gently, until the deep blue color disappears. Notice that the cellulose is reprecipitated in a stringy, amorphous condition. * Tliis acid is especially corrosive ; it should be used carefully, and carefully replaced on the shelf. Fig. 1.— Potato Starch, x 100. With- out and with polarized light (Dr. E. G. Love). Fig. 2.— Corn Starch, x 320. With- out and with polarized light (Dr. E. G. Love) . LESSON 11. DEXTRIN, GLYCOGEN AND GLUCOSE. THE DEXTRINS.— (C6H,o06)n. In the process of conversion of starch or of cellulose into the simpler compounds, maltose or glucose, by the action of either heat, chemical agents, or ferments, a series of intermediate prod- ucts are formed, known as dextrins. Some authorities claim that the different individuals of this group can be accurately separated and recognized by their behavior with polarized light, the colors they give with iodine solutions, and other properties. They have even given names to them, in some cases simply call- ing them «, /?, and y dextrins ; in other cases naming them after their reaction with iodine, as Achroo (colorless) or Erythro (red) dextrins ; or, according to their source and general chai'acteristies, as Amylo (starch) or Malto dextrins. In the opinion of others the dextrins are simply mixtures of granulose or soluble starch with varying proportions of maltose or glucose. Occurrence and Preparation. — Dextrin, in one variety or another, occurs to some extent in nature associated with eane sugar and the glucoses. It is prepared pure on a large scale either by heating finely ]iowdered dry starch, with constant stirring, until it gets brown, a temperatui'e of from 225-200" C. being the best for this purpose ; or else by first soaking the starch in very dilute nitric acid (1 or 2%) and then drying it thoroughh' at a temperature of 100' or 110' C. It is also formed as an intermedi- ary product in the digestion of starchy foods, in the manufacture of beer and alcohol, and in the conversion of starch into dextro- glucose or corn sugar. In the latter case it enters very largely into the finished product in the form of syrups or li(|uid glu- cose. Properties. — All of the dextrins are easily soluble in water. 14 MEDICAL CHEMISTRY. making a clear, sticky solution; they dissolve somewhat in dilute but are insoluble in absolute alcohol. They are structureless, and more or less sweet to the taste. They rotate the ray of polarized light to the right, the specific angle of rotation for the yellow sodium ray, known as [«jd, being from -\- 170° to + 195°. This angle, in every case, is the amount of rotation produced by a column 1 decimetre long of a solution of 1 gramme of the sub- stance in 1 cubic centimetre of a non-active solvent. "With diluted iodine solution they give various shades of color, from the purplish blue of the amylo-dextrin, which is hardly to be distinguished from the granulose of starch, through the brown and red of the erythro-dextrins, to the almost colorless compounds made with the malto-and achroo-dextrins, which ai'e much like maltose and dextrose. They are easily broken down to maltose or glucose by boiling with water or, more rapidly, with dilute acids ; by the action of stronger acids, and also of the various am ylolytic ferments, such asptyalin, amylopsin, diastase, and others. When pure, they do not undergo alcoholic fermen- tation, but in the presence of some fermentible carbohydrate, they ferment readily and thoroughly. This is probably due to the secretion by the yeast plant of a special ferment, which acts like diastase and the others in reducing the dextrin to maltose. Uses. — Dextrin is more or less valuable for food; toast, the crust of bread, and the different kinds of prepared infants' foods, are common examples of its use. It has the advantage over starch of already being partially digested. It also enters into the man- ufacture of beer and alcohol. It is very largely used as a sub- stitute for the different gums, especially gum arable which it closely resembles, in the preparation of mucilage, in dyeing and calico printing, and in the finishing and glazing of cards, wall paper, and similar articles. GLYCOGEN.— CoHioOs, or perhaps CaeHo^Oai. Although the experiments on this svibstance will be made in a later lesson, it is proper to briefly describe it before leaving this class of the carbohydrates. Occurrence. — Glycogen, or liver dextrin, as it is sometimes called, is the peculiar carbohydrate found in the livers of all GLYCOGEN. 15 animals, and also, in smaller quantities, in the muscles and other organs, especially in foetal life. It occurs, in some instances in considerable abundance, in certain shell-tish, such as mussels and oysters. It has also been found in the vegetable kingdom, principally in some of the varieties of fungi and other low orders of plants, e. g., in the counuon truffle, in Mucor Mucedo and other mould plants, and perhaps in the yeast plant. Preparation. — It is best prepared from the livers of rabbits or dogs that have been well fed, for some days, upon a carbohy- drate diet. Directly after the animal is killed the liver must be taken out, cut into small pieces and plunged into boiling water, to prevent the glycogen fermenting into glucose. The pieces are then hashed or ground up as fine as possible, stewed in the same water for some minutes, strained, and then the proteids separated by, among other reagents, hydrochloric acid and mercury potassium iodide. The glycogen is then precipitated from the aqueous solution by an excess of alcohol. Properties.— It is claimed by some experimenters that, by valuations in feeding, different varieties of glycogen can be ob- tained. This is probably, however, due to the presence of im- purities derived from the liver. Glycogen, as we jneet it, is quite similar to the higher (/. e., starch-like) memhers of the dextrin group, and, like them, can be readily changed to other dextrins and to maltose and glucose, by heat, dilute acids, and ferments. In fact, our theoiues with regard to this substance demand the presence of two ferments in the liver, the one to form glycogen from the maltose and glucose of the i^ortal vein, and the other, which is present after death and acts quite rapidly, to change it into glucose again as needed by the system. It is a white, amorphous powder, easily soluble in hot water, and has the following characteristic; reactions : 1st. Its solutions are opalescent, not clear. They can be cleared by potash or acetic acid. 8d. Its solutions are colored red or l)rown by iodine, the color disappearing, as in the case of starcb, on heating or on the addition of an alkali or various metallic salts. 16 MEDICAL CHEMISTRY. 3cl. Its solutions polarize stronglj" to the right, [oJd being about +211\ 4th. Its solutions are precipitated by alcohol. Uses. — Glycogen seems to be of the utmost importance in physiology, in enabling the liver to act as a reservoir of carbo- hydrate food. During digestion an excess of sugar is poured into the system thi-ough the portal circulation, but instead of going at once all over the body it is changed to glycogen in the liver, and given out slowly and regularly from there into the general circulation. Glycogen is also formed in the liver by both proteids and fats. During a period of fasting the store of glycogen in the liver is probably the first to be called upon. It is supposed to bear an intimate relation with certain morbid conditions of the body, such as diabetes mellitus, but this has not yet been accurately determined. THE MOXO-SACCHARIDS OR GLUCOSES.— CoH.oOe. Leaving to the next lesson the class of di-saccharids or sugars proiDer, we come now to the class of mono-saecharids or glucoses. These are the simplest in structure of all the carbohydrates, and are produced by the breaking down of the higher members. DEXTRO-GLUCOSE OR DEXTROSE. {Grape Sugar) (Corn Sugar.) This substance is so much better known and more widelj^ disseminated than any of the other members of the class that in common language it has practically monopolized the word glucose. Its name dextrose is derived from its property of "polarizing" to the right. Occurrence. — It is found widely scattered in the vegetable king- dom, genei'ally associated with an equal quantity of lacvulose, and forming the so-called Invert Sugar. It occurs largely in sweet fruits, grapes, plum.s, figs, etc.; and the sugar that crystallizes out of these fruits when dried, as in raisins, for instance, is either dextrose or a loose combination of dextrose and Uevulose. It also occurs in the juices from every part of plants, and is present in considerable (juautities in honey, though whether coming directly from the nectar of flowers, or produced bj"^ fermentation from DEXTRO-GLUCOSE OR DEXTROSE. 17 cane sugar or other carbohydrates, it is hard to say. It is found in raw sugar, l)oth from the beet and the sugarcane, in molasses, in the pecuhar manna sugar, in crude gums, and, in fact, in ahnost every vegetable extract. In the animal kingdom it seems to be the form in which the carbohydrates are absorbed into the circulation. Accordingly we find traces of it in the blood, especially in that of the portal vein. It also seems to occur in hens' eggs, and in the liver, where it is probaljly derived from glycogen. It must be remembered in this connection that it is impossible, in small quantities, to dis- tinguish it from uialtose or from lactose, either of which may be equally present. There is no doubt, however, that it occurs, often in large quantities, in the urine of patients suffering from diabetes mellitus, and forms the essential feature of the disease. Preparation.— Dextrose is formed in nature by the breaking down of cane sugar, or in some cases of maltose or glycogen. It is manufactured on a large scale by heating starch or cellu- lose with dilute acid, as Illustrated in Lesson III. Properties. — Dextrose occurs in commerce in two forms, as an- hydrous dextrose (C6Hi.j06) and as the hydrate (CeHisOe + H^O). The latter is formed when dextrose is allowed to crystallize in the cold from a water solution ; the former, when the solution is heated. Both these forms are crystalline, and by careful heating the latter loses its water and becomes anhydrous without chang- ing its form. Both varieties p:larize to the right, [(/]d for a solu- tion of the hydrate being +48.2', and for the anhydrous dextrose -1-53. 1'. Dextrose is not more than one-half as sweet as cane sugar. It is very soluble in water, easily soluble in dilute and slightly in absolute alcohol. It diffuses easily. With yeast it readily ferments to alcohol and carbon dioxide, but other microbes produce in it sometimes alcoholic, frequently lactic, butyric, and other fermentations. Uses. — Dextrose is principally used as a food, either in the form of fruits, molasses, honey, etc., or in a moreinu'e form. Dry dextrose is sometimes employed as an adulterant of cane sugar, this depending largely on the relative price of the two, and is nmch used to take the place of cane sugar in confectionery. The dextrose syrups are largely used instead of molasses, and also in 18 MEDICAL CHEMISTRY. the production of artificial honey, the adulteration of beer, pre- serving fruits, and strengthening wines and vinegars. Some dex- trose is also used in the manufacture of printers' rollers, of copy- ing inks, and of caramel or sugar color. L^VULOSK— CeHisOe. Occurrence. — This glucose is found associated with dextrose and cane sugar in sweet fruits, molasses, raw sugar, honey, and in the various vegetable juices. It is usually in the combination with dextrose known as invert or fruit sugar, i-esulting from the hydration of cane sugar. Preparation. — Lsevulose can be prepared in a pure form only with very great difficulty, either from invert sugar or from certain carbohydrates such as inulin, which, on breaking down, produce IsBvulose just as starch produces dextrose. Properties. — It is possible to obtain it in the form of fine needle- shaped crystals. Ordinarily on evapoi'ation it forms a thick syrup, which not only refuses to crystallize itself, but has the property of keeping in solution considerable quantities of dextrose and cane sugar, which would otherwise crystallize out. For this reason the formation of invert sugar in the process of refining cane sugar is guarded against as much as possible. The name lsevulose was given to it from its property of polar- izing strongly to the left, [a]D for a solution of the pure crystals at 20' C. being equal to —71.4°. In other respects it strongly re- sembles dextrose, resiionding to the same tests and fermenting in the same manner. GALACTOSE.— CeHiaOo. This glucose is formed, along with dextrose, by the breaking down of lactose and also of some rarer carbohydrates by boiling with dilute acids, or by the action of certain ferments. It crystallizes in small six-sided crystals ; it polarizes to the right more strongly than dextrose, [ajc, at 20° C, being equal to 80° it responds to all the glucose reactions, and it undergoes alcoholic fermentation more or less readily. Its chief interest to us is in connection with the manufacture of koumyss. TESTS FOR GLUCOSE. 19 TESTS FOR GLUCOSE. The more important tests for glucose may be divided up into five principal classes, according to whether they depend upon — (a) The action of alkalies. — Moore's test. {h) The reaction with hydrazin compounds. — Phenyl hy- drazin test. (c) The reduction of metallic and other co77ipou7ids. — Bis- muth subnitrate, picric acid, Trommer's and Feh- ling's tests. (d) Alcoholic fermentation. (e) The polariscope. Taking these up in the above order v/e have — 1st. Moore's Test. — When glucose, either dry or in solution, is heated with a powerful alkali, it rapidly decomposes into a va- riety of different substances, some of which— acetol, acetone, and others— are light volatile liquids, others of which are the ordinary formic, acetic, and lactic acids, and still others are brown-colored amorphous bodies, as yet little investigated, but described as com- pounds of humie and other acids. The latter give the mixture a decided yellow or brown color, which, on acidifying with nitric acid, disappears more or less completely, leaving behind a peculiar odor of caramel. On this reaction is based the simplest of all the glucose tests, where the suspected liquid is heated to boiling, with the addition of caustic alkali. It is best, in practice, to heat only the top part of the mixture, so that any change of color is at once noticed ; this is especially important when dealing with samples of urine, which generally have a decided yellow or brown color at the start. It is always advisable to confirm the result with nitric acid. The test is not a very delicate one, and is rather unreliable in testing urines, not only because the mixture is colored more or less deeply to start with, but also because the same re- action sometimes occurs with normal constituents of the urine, notably with mucin. 2d. Phenyl Hydrazin Test. — This test, which was introduced by Fischer in 1884, depends on the formation of a compound known 20 MEDICAL CHEMISTEY. as Phenyl Glacosazon, by the action of glucose on an excess of phenyl hydrazin (CeHs. NH. jS'H.). "NYhen dilute solutions of these two substances are mixed to- gether in the presence of acetic acid, and heated, the following reaction takes place : C6Hi206 + 2C6H5N,H3 = C,Hio04(C,H5N.,H)2+2H,0+Hi, Dextrose. Phenyl Hydrazin. Phenyl Dextrosazon. The hydrogen set free in this reaction does not escape, but at- tacks some phenj'l hydrazin, changing it to anilin and ammonia. The j)henyl dextrosazon, which is jDrecisely similar to phenyl Isevulosazon formed from Isevulose, and is often called phenyl glucosazon, consists of yellow needle-shaped crystals, which melt at 204 or 205" C, are insoluble in boiling alcohol, dissolve only slightly in water, reduce Fehling's solution, and polarize slightly to the left. They are readily recognized by their appearance under the microscope, and are distinguished by that and by their melting point from similar compounds with other carbohydi'ates. This test is an extremely delicate and an extremely accurate one, giving reliable results where other tests fail. 3d. Bismuth Suhniirate Test. — This and the following tests de- pend upon the reduction or deoxidation of various compounds, both organic and inorganic, in alkaline solutions, by the action of glucose. As is seen by the formula CeHiaOe, there is only enough oxygen present in glucose to burn up the hydrogen, and consequently it will, under favorable circumstances, act as a powerful reducing agent, «.e., take oxygen away from other bodies. In the present test bismuth subnitrate, BiCOHjzNOs, is reduced to bismuth suboxide, BiaOo, which forms a characteristic cloudy black precipitate. The original method of making the test was to mix with the suspected liquid an equal bulk of carbonate of soda solution and a pinch of dry subnitrate, and then to boil it. It is more satisfactory to use Nylander's modification of this test, when the bismuth salt is dissolved in an alkaline solution of Rochelle salt. The Nylander's solution is composed of 4 parts Rochelle salt, 10 parts caustic soda, and 2 parts bismuth subnitrate, in 100 parts of Avater. The soda in this makes the solution alkaline, and the Rochelle salt keeps the bismuth dissolved. TESTS FOR GLUCOSE. 21 This test is not so delicate as some of the others, and has the serious disadvantage of reacting with other substances, sulphur (from albumin) and various reducing compounds, which not un- commonly occur in urine. 4th. Picric Acid and Potasfi Test— When a solution containing glucose is boiled with an alkaline solution of picric acid or trinitx-ophenol, CeHj. (N02)3. OH, the latter is reduced to picramic acid, CeHa (NOj)^. NH2. OH, with the production of adeep brown or even black color. This reaction must not, however, be mistaken for the slight change in color Avhich results from boiling picric acid and potash together by themselves. This test is one of the most delicate that we possess, and is specially important to a student of medicine, because picric acid not only reacts for glucose, but also, as is seen later, is an excel- lent reagent for albumin. Kreatinin and some similar com- pounds, and acetone, which also may occur at times in urine, respond to this test in the same manner as glucose. 5th. Trommefs Test.—T\\\% test, as well as Fehling's test, which follows, depends upon the reduction by glucose of an alkaline solu- tion of cupric hydrate, Cu(0H)2, into the yellow cuprous hydi'ate, Cu2(0H)o, and finally, by continued boiling, into red cuprous oxide, CunO. In Trommer's test an excess of potash is first mixed with the suspected fluid, and afterwards cupric sulphate is slowly added, producing at once cupric hydrate. The latter is a bluish- white precipitate, insoluble in potash, but dissolving in a solu- tion of glucose. Hence if any glucose is present a deep blue solu- tion resi;lts. To obtain the best results the mixture must be saturated Avith the Cu(0H)2. The characteristic yellow and red cuprous salts result slowly in the cold, but almost instantaneously on heating. Both this test and Fehling's test are delicate and useful, but they respond to many substances, uric acid, kreatinin and others, which often occur even in normal urines. Gth. Fe/iliitf/s 7V.yf.— This test is like Trommer's test excepting that Rochelle salt, and not glucose, is depended on to keep the cupric hydrate in solution. Fehling's solution consists of a mixture of cupric sulphate, Rochelle salt, and caustic alkali ; 23 MEDICAL CHEMISTRY. but as this mixture is constantly liable to decompose, especially when exposed to light, it is far preferable to keep the cupric sulphate in one solution and the Rochelle salt and alkali in an- other. These solutions are made of the following strength : 500 e.c. of the cupi'ic sulphate solution contain 34.64 grammes of crystallized CuSOj. 500 c.c. of the Rochelle and J 187 grammes of Rochelle salt, soda solution contain — ( 68 "■ of sodie hydrate. Fehling's solution proper is made by mixing together equal quantities of these two solutions. To make a qualitative test it is only necessary to mix a few drops of the two solutions, dilute more or less with water, boil thoroughly, and add a little of the suspected fluid to the boiling mixture. It is always advisable to boil the solution thoroughly before making the test, as a safeguard against error. To make the test more delicate it is only necessary to use a more diluted Fehling's solution. When carefully made, the test is extremely delicate. It fails, howevai% now and then when dealing with im- pure and putrid solutions, such as stale pathogenic urines. QuA^'TITATIVE DETERMINATION OF GLUCOSE. FeliUng's Test. — To use the Fehling's solution for a quantitative test, advantage is taken of the fact that a certain amount of glucose is always necessary to decompose any given amount of cupric sulphate, and that when the cupric sulphate is all decomposed the solution loses its blue color and becomes colorless. The copper solution is made of such a strength that 5 c.c. of it are exactly decomposed by 0.05 gram of dry glucose. Hence, whenever, in making the test, we add enough of the liquid we are testing to destroy the blue color in 5 c.c. of the copper solution, we know that we have added at the same time, dissolved in that liquid, 0.05 gm. of glucose. If we have to add 1 c.c. of the liquid before the color disappears, then there is 0.05 gm. glucose in 1 c.c. of the liquid, or 5 gms. in 100 c.c; in other words, the liquid will contain Ti% of glucose.* If 2 c.c. are needed before the color disappears the liquid is only half as strong, and contains only 21%. If it takes 5 c.c. the strength of the liquid is only \%. Hence, in general, * The correction for difference of specific gravity is too small to be taken into consideration. DETERMINATION OF GLUCOSE. 23 the percentage of glucose in the liquid to be tested will be always equal to 5, divided by the number of c.c. of liquid used. This Fehling's test can, with care, be made with considerable accuracy. The principal error is in not knowing just when to stop adding from the burette. The solutions, burette, pipette, flask, etc., should all be kept scrupulously clean ; and the Fehling's so- lution, diluted, and with a piece or two of pumicestone in it to prevent bumping, should be thoroughly boiled both before and during the addition of each drop of the test liquid. The latter should be added at first drop by drop, and only when the reaction has satisfactorily started can it be run in at all rapidly. The pre- cipitated cuprous conqjounds should appear first of a purplish color, then, as more and more of the copper salt is decomposed, they get more and more red, till they finally give the liquid a bright vermilion color. That marks the end of the reaction. To make sure of not adding too much glucose solution, the precipitate slionld be allowed to settle now and then, and the color of the supernatant liquid observed while still hot. If allowed to cool, some of the cuprous salt will oxidize again. The liquid should be practically colorless. If bluish it shows that some of the copper is still unreduced, and more test liquid is needed. If too much glucose, however, has been added, the liquid has a yellowish or even brownish look from the action of the alkali on the glucose. Now and then, in spite of every pre- caution, the solution turns a muddy greenish color directly the test liquid is added, and then often no subsequent treatment will save the test. This is especially the case in urine analysis, and is the chief o1)jection that can be raised against this method of analysis. The subject of alcoholic fermentation, both by itself and as a test for glucose, will l)e discussed later. Before leaving this topic, a word should be said about the polariscope method of testing for glucose. The polariscope is is an instrument for determining the exact angle of rotation of any particular solution. If this is found, and if we know the length of the test column and the specific angle of rotation of the substance tested for, we can easily calculate the strength of the solution. For scientific and commercial analvses of carbo- 24 MEDICAL CHEMISTRY. hydrates, and especially of cane sugar, this is by far the most ac- curate and most convenient method; but in medical ijractice it is of but little value as compared to the tests described above, partly because it needs an expensive and more or less complicated piece of apparatus, but principally because, before using it, the liquids to be tested have to undergo a tedious and elaborate system of decoloration. Another sei'ious disadvantage is the frequent presence in urine of various organic substances which have a decided and often a reverse action on polarized light. LABORATORY EXPERIMENTS. DEXTRIN AND GLUCOSE. I. Dextrin. — Two samples. Test each sample as follows : (a) Taste it. (&) Dissolve it in water; notice that it is sticky and gummy. (e) Half fill a test-tube with alcohol, and add one di"op of dextrin solution = a white precipitate (ppt.). Add some water ; the ppt. dissolves. (d) Place some dextrin solution in a test-tube and add some iodine solution diluted three or four times with water. Notice the red "claret" color with the one dextrin and the brown color with the other. II. Glucose.— Qualitative Tests. — Test glucose as follows : (a) Taste it. (b) Dissolve it in water. On this solution make the follow- ing tests : 1st. lloore's Test.—Vut some solution in a test-tube and add one- thii'd as much KOH. Boil the upper layer of the solution = brown color. Notice the smell of caramel. Add a little con- centrated nitric acid (HNO3 cone.) and the color will disappear. 2d. Phenyl Hydrazin Tesii.— Measure out with the tip of a pen- knife blade two parts of phenyl hydrazin (hydrochlorate) and three parts of acetate of soda, and put them in a small test-tube. Fill the tube two-thirds full of glucose solution, dissolve the TESTS FOR GLUCOSE. 25 salts by warming them gently and by agitation, and then stand the test-tube in boiling Avater in a waterbath for twenty or thirty minutes. After this take it out and put it into a beaker of cold water. Notice, as it cools, the formation of a y^ He w crystalline ppt. of phenyl gkicosazon. Let the ppt. settle, especially if the solution is very dilute, and examine it under the high and low powers of the microscope, noticing the radiating groups of yellow needle-shaped crystals. 3d. Bismuth Suhnit rate Test {Nyl finder's Test).— Vnt m a test- tube some glucose solution and boil. To the boiling liquid add half an inch of Nylander's solution. Boil for two or three minutes more and let it stand. Notice the black ppt., which appears at once if the glucose solution is strong, and moi'e slowly if it is dilute. 4th. Picric Acid and Potasti Test. — Put some water in a test- tube, add a few drops of picric acid and half an inch of KOH and boil. Notice that the color changes somewhat, although no sugar is present. In another test-tube put a little glucose solution, add the picric acid and KOH, and boil. Notice that the color changes at once to very dark brown or black. 5th. Trommer's Test. — Put some of the glucose solution in a test- tube and add about one-fourth its volume of KOH. Then add the cupric sulphate (CuSOj) drop by drop, shaking constantly, until the bluish-white ppt. of cupric hydrate, Cu(0H)3, just ceases to dissolve and makes the liquid slightly turbid. Set the mixture aside, let it stand, without warming, and notice that a yellow ppt. slowly forms in the course of fifteen or twenty minutes. Repeat the test in another test-tube, and boil the mixture. It will give a red or yellow ppt. at once. 6th. Fehling's Test. — Mix equal parts of CuS04 and of " roehelle and soda" solution together in a test-tube. The deep blue mix- ture is Fehling''s solution. Put a few drops of it in a test-tube, add a little water, and boil. To the boiling liquid add a drop or two of the glucose solution, and keep it boiling. It will give a yellow and then a red ppt. Repeat these five tests with more and more dilute glucose solutions, observing the comparative delicacy of each test. Also, 26 MEDICAL CHEMISTRY. if you have time, examine both grape juice and raisins for glu- cose with the test you pi-efer. QUANTITATITE DETERMIIfATION OF GrLUCOSE. — FeMilig'S Method. — Take witli a pipette 5 cubic centimetres (c.c.) of the CuSO, and place in the flask. Rinse the pipette, then take with it 5 c.c. of the " rochelle and soda" solution and add them to the same flask. Fill the flask one-third full of water, add a piece of pumice stone, and boil. While this is heating, fill the burette to the zero mark with the "test glucose solution" ; and when the copper mixture is boiling, add to it some of this solution, drop by drop, from the burette. Every minute or two stop boiling, let the ppt. (which should be red) settle, and notice if the blue color has disappeared from the liquid in the flask. If it has not, boil again, add a few drops more of the glucose solution, and examine the color. When the blue color has entirely disappeared, read on the burette the number of c.c. used, and calculate the percentage of glucose in the solution by the following rule : " The percentage of glucose in the solution is equivalent to 5 divided by the number of c.c. of solution used." Repeat this experiment with a dilute solution of the solid glucose. LESSON III. CONVERSION OF STARCH INTO DEXTRIN, GLUCOSE, AND MALTOSE. FERMENTATION. THE CONVERSION OF STARCH INTO DEXTRIN, GLU- COSE, AND MALTOSE. The following experiments illustrate the more important meth- ods of breaking down .starch into the simpler carbohydrates. Preparation of Dextrin. — In Section I. is shown one of the ordinary ways of preparing dextrin on a large scale. The starch granules begin at from 150' to IGO" C. to lose their chai'acteristic structure, to get yellow and even brown in color, and to become more or less completely soluble in water. After keeping at this temperature for some time, the conversion is almost complete. The addition of even a trace of nitric acid assists greatly the formation of the erythro dextrins. In commerce, this heated starch is generally extracted with water, and the solution evaporated and heated a second time. In the laboratory much of the dextrin produced isamylo-dextrin, which greatly resembles and gives the same color with iodine as the soluble starch of Lesson I. In order to recognize the presence of the erythro-dextrins, it is often neee-ssarj^ to make the dextrin solution very strong and the iodine solution very weak, and, if the resulting color is purplish blue, to add more dexti'in solution to the mixture till the blue just disappears, when the red or brownish color may be seen. Manufacture of Glucose.— In Section II. is illustrated the regular method of manufacturing commercial glucose or corn sugar. The pure starch which is prepared in large quantities, usually fx'om Indian corn, is boiled, often under pressure, with diluted acid. Sulphuric and oxalic acids are the ones most commonly employed, because they can be most easily and 28 MEDICAL CHEMISTRY. cheaply removed from tlie solution afterward. AVhen the eon- version has proceeded far enough — a question determined in practice, as in our lesson, by noticing- the color given by iodine —the acid is neutralized and precipitated by the addition of either limestone, CaCOs, or, in our case, of barium carbonate. The acid combines with this, forming calcium or barium sulphate, and liberating carbon dioxide, according to the formula, H2SO4 + BaCOa = BaS04 + CO2 + H^O. This sulphate is removed by either settling or filtration, and, on evaporating the clear solution, the dexti'ose will crystallize out. Where syrup is desired, and not dry glucose, the conversion is stopped while some dextrin still remains, and the solution is not concentrated so far. The Action of Ferments on Starch. — Sections III. and IV. illustrate the action upon starch of two of the most important amylolytic ferments, diastase and ptyalin. These ferments have the power of changing starch into dextrin and maltose, and finally into dextro-glucose. The ferment known as diastase is found in all kinds of grain when sprouting, although it is most commonly obtained from malt, i.e., barley allowed so sprout a little, and then dried at a temperature high enough to kill the plant but not destroy the ferment. The diastase seems to be formed from the albuminoids around the embryo just when the young plant com- mences to grow, and it plays, as mentioned before, a most im- portant part in digesting the starch previously stored up in the seed or tuber. There is enough diastase, however, in the malt, not only to digest the starch in the grains themselves, but also to convert many times their bulk of fresh starch. The ptyalin ferment, existing in the saliva, plays rather an unimportant part in the digestion of the carbohydrates. It acts in the same manner as diastase, only not so powerfully, being unable to attack uncooked starch grains. It acts best at a some- what lower temperature than diastase, at about 40° C. as comj^ared to 50° or 55° C, and is nearly inactive at the temperatures 60°-65° C, at which, in practice, malt is usually employed. Both act best in neutral rather than alkaline solutions ; their action is stopped by BODIES ACTING LIKE FERMENTS. 29 free acids even in small quantities, they are killed by boiling, and are seriously affected by various toxic agents. FERMENTATION. Before leaving this suliject, it is worth while to discuss briefly the properties and actions of some of the more important fer- ments that we shall meet in the course of these lessons. The subject of fermentation has been an important one from the early ages of chemistry. The name was derived from the boiling or bubbling of the carbon dioxide, early noticed in the production of alcohol, and was given at first to almost any process of nature involving change of form or substance which could not be readily explained. Fermentation was the name which covered not only all kinds of decomposition and putre- faction, but also the formation of blood and secretions, the pro- duction of heat and cold in the body, and even all kinds of dis- ease. Toward the end of the last century the different kinds of larmentation proper were more carefully studied, and the discus- sion as to the true nature of alcoholic fermentation began then, only to be finally settled in comparatively recent times. Classification of Ferments in General.— At present wa may define a ferment as a chemically active body, a small amount of which transforms large quantities of other substances without itself apparently contributing anything to the reaction. Under this definition we may divide ferments up into three general groups — 1st. Bodies acting like ferments. 2d. Unorganized ferments, enzymes. 3d. Organized ferments. BODIES ACTING LIKE FERMENTS. The substances that are included in this first class have to do with several very important chemical reactions, which were long unexplained. One of the most jDrominent of them is the substance nitrogen peroxide, NO2, which, with the accompanying N2O3, plaj^s such an important part in the manufacture of suli)huric acid. As 30 MEDICAL CHEMISTRY. Avill be remembered, in order to oxidize SO2, sulphurous anhy- dride, into SO3, sulphuric anhydride, the nitrous fumes, as they are called, are necessary to act as carriers of oxygen from the atmosphere to the sulphur vapors. These fumes, however, are not destroyed in the operation : they give up oxygen to the SO2, and take it again from the atmosphere, and at the end of the process there is, theoretically, as much of the nitrogen peroxide as there was to start with, although immense quantities of sul- phui'ic acid may have been manufactured in the mean time. In other words, the nitrous fumes have played the part of an unorganized ferment. Another example is the use of sulphuric acid in the manu- facture of ethylic or sulphuric ether. Another is the action of salts of copper in the so-called Deacon's chlorine process. These reactions, however, can all be explained by imagining an intermediate reaction, in which the active agents take part, only to be set free again in a later stage. UNORGANIZED FERMENTS. It is possible that the unorganized ferments or enzymes do their work in some similar manner. These substances are all amor- phous nitrogenous bodies, readily soluble in water and generally precipitated by alcohol. They occur in both animals and plants and seem to be secreted by cells in the tissue where they belong. Probably in all instances, certainly in many, as in the case of pepsin, rennet, and others, these cells secrete a zymogen, i.e., a substance inactive of itself, but which, in the presence of HCl or other media and under suitable circumstances, is changed into the ferment. They are prepared, generally, by extracting them from their source by means of water, salt solutions, diluted acid (especially hydrochloric), and, best of all, by glycerin. It is difficult to ob- tain them in a pure form ; they are rarely free from proteids and from mineral matters. So far as we can tell, though, their com- position is much the same as that of albumin, with, generally, less carbon and more oxygen. It is noteworthy that, while of UNORGANIZED FERMENTS. 31 extremely complicated structure, they are often much less liable than the proteids to undergo decomposition. Their action depends very largely upon external conditions such as temperature, reaction, presence or absence of certain chemicals, etc. With regard to temperature, each ferment has its limits within which it acts, its temperature of maxiumm efficiency and its death temperature. They stand dry heat much better than moist heat. It is possible that their destruction in the latter case is caused by coagulation. Classification. — The unorganized ferments that have been so far isolated may be classified as follows: I. Inverting ferments. — Invertin. II. SaccJiarifyiny (diastatic, aniylolytic).— Diastase, ptyalin, amylopsin. III. Ghicoside decomposiny. — Emulsin, myrosin. IV". Peptonizing. — Pepsin, trypsin, papain. V. Coagulating.— Rennet, fibrin and myosin ferments. VI. Fat-deeompo.^ing. — Steapsin. Inverting Ferments. — These have the power of inverting cane sugar, i.e., of changing it to dextrose and Isevulose. Fer- ments of this sort have been found in the gastric and intestinal juices, from which it is supposed that cane sugar is changed to glucose in the process of digestion. The most important ferment of this class, invertin, is extracted by water from yeast, either dead or alive, and, from its relations to the theories of fermenta- tion, has been studied very carefully. It enablesyeast to ferment, although slowly and indirectly, a solution of pure cane sugar. Saccharifying Ferments. — These have already been some- what discussed. They decompose starch, erythro-dextrin, and glycogen into maltose and achroo-dextrin, and will, on further etanding, decompose some of the maltose into dextrose. The amylopsin, which is derived from the pancreatic juice, is more powerful in its action than ptyalin, which it otherwise very closely resembles. Besides the three important ones already njentioned, ferments of this class have been found in the liver, intestinal juice, red blood cells, and other organs of the body, and in many parts of plants. Glucoside Decomposing Ferments. — The ferments belong- 32 MEDICAL CHEMISTRY. ing to this class decompose a peculiar series of vegetable com- pounds known as glucosides. These glucosides, of which a great number are known, and some of which have been manufactured synthetically, have the property of decomposing, when warmed with dilute acids or when treated with the proper ferment, into a glucose and some other body. The glucose is usually dextrose; but in some cases very peculiar members of the group result, which are obtained in no other way. The best known ferments of this group are emulsin, Avhich is found in sweet and bitter almonds, and myrosin, found in black mustard seeds. Peptonizing Ferments.— The action of this class of ferments will be discussed later under Lesson XXI. It is only necessary to say here that they are able to break down the proteids and some albuminoids into diffusible compounds. The pep- sin, which is obtained from the gastric juice, acts best in a solution of hydrochloric acid, preferably 0.2%, and but partially accomplishes the digestion of the proteids of the food. The work is carried forward by the trypsin of the pancreatic juice, working in an alkaline or neutral medium. The papain is a vegetable digestive ferment, which digests proteids in the same way as pepsin, but only works in a slightly alkaline or neutral solution. Coagulating Ferments. — These will also be discussed later. The rennet ferment, which coagulates the casein of milk, exists in the stomachs of all infant mammalia, for the purpose, it is supposed, of making light and easily digested coagula of the milk ingested. The true nature of the fibrin and myosin ferments is still to be d3termined. About the steapsin of the jjancreatic juice, mentioned under the sixth class, but little is as yet known. For although several experimenters have observed that fat is broken up in digestion into fatty acid and glycerin, the ferment proper has not been isolated, nor is it even agreed that such decomposition is neces- sary for the digestion of fat. ORGANIZED FERMENTS. 33 ORGANIZED FERMENTS. The ferments disoussi'd so f;ir have all been true chemical sub- stances, producing their effects by the agency of what we now beheve to bepurely chemical means. There remains, however, the most important group of all, namely, the Organized Ferments, living organisms, which feed upon the substances they decompose, and change them either in their own cells, or at any rate as a part of their hfe process. These microscopic beings, which are now generally grouped together under the name microbes, are divided into three classes— the mould plants, yeast plants, and bacteria. Mould Plants. — These are microscoijic fungi, growing and propagating like the larger memljers of the family, i.e., the ordi- nary mushrooms, puffballs, and toadstools. The gi'owth, and hence the work of these plants is done by the root, or mycelium, consisting of long, slender, white, branching fibres, which under the microscope are composed of long c^'lindrical cells, rather irregular in shape, adhering one to the other. This mycelium honeycombs the material attacked if a solid, or forms white floating masses through it if a liquid, as long as all conditions are favorable. But when, either from drying up, or failure of food, or any other cause, the active growth is impeded, little white stems apj^ear here and there from the surface of the my- celium ; little heads form on these, which gain a characteristic color as they ripen, and which finally burst, scattering the minute spores into the air. To these microbes are due all the phenomena of moulding and much of the ordinary decomposition and decay. Yeast Plants. — These belong to a much lower order of life. They consi.st of a single cell, with a cell-wall which consists, it is supposed, of cellulose. They are about the size of one of the cells in a piece of mycelium, i.e., describing them roughly, they can be seen with a two-thirds and studied with a one-sixth objective. There are several varieties of them, which differ in size, shape, and especially in action from each other. They look under the microscope like white grapes, single and in bunches. They propagate by budding, the buds sometimes adhering to the indi- 34 MEDICAL CHEMISTRY. vidual cell, sometimes separating. They stain quite readily with fuchsin and some other dyes, showing two or three nuclei inside them. They are the active agents in alcoholic fermentation, and also in many other fermentations of less importance. Bacteria. — These form the smallest class of microbes, need- ing a high magnifying power — a one-sixth objective, for example — even to distinguish them. They occur in a variety of shapes, from the round micrococci, through the rod-like bacteria and bacilli, to the curved spirilla and spirochsetae. They propagate by division, i.e., the parent cell enlarges and divides across the middle, making two bacteria, both of which can proceed to multi- ply in the same manner. Some varieties of them also propagate by forming spores. As we see them in liquids they are in con- stant motion, due partly to the so-called Brownian movement, partly, it is supposed, to individual efforts. They will be found, in these lessons, in great abundance in all organic fluids which have been exposed to the air or have stood unsterilized for any length of time. LABORATORY EXPERIMENTS. CONVERSION OF STARCH INTO DEXTRIN, MALTOSE, AND OLUCOSE. I. Into Dextrin by Dry Heat. — Put half a spoonful of dry powdered starch on the agate plate placed on a sand-bath. Moisten the starch with a solution of one drop of dilute nitric acid, HNO3 dil., in a small test-tube full of water. Heat it very gradually, stirring the starch constantly with a knife. When it is well broAvned, dissolve some in water, filter, and test the clear solu- tion as follows : (a) Add a drop of diluted iodhie solution ; notice the resulting color, usually red or brown, although often blue if too much iodine is added. {b) Fill a test-tube half full of alcohol, and add one drop of the solution. Usually, though not always, a white ppt. ap- pears. .PREPARATION OF DEXTROSE AND MALTOSE. 35 II. Into Dextrin and Dextro-glucose by Boiling "with Acid. — Fill the agate cup half full of water and heat to boiling. While it is heating, grind up all the remaining starch to a milk with cold water. Add gradually to the boiling water enough of this starch to form a stiff paste, when thoroughly stirred in. Reserve enough of this paste for tests III. and IV. below. To the rest, in the cup, add 10 c.c. of H2SO4 dil. and boil for an hour or so. Every few minutes take out a few drops with a pipette and test for dextrin by adding to it a drop or two of much diluted iodine solution. Notice that the resulting color is at first blue, but after more pro- longed boiling it changes to red or brown, and finally hardly any color at all is produced. Then neutralize with the milky solution of baric carbonate (BaCOs) till blue litmus paper, dipped in the liquid, no longer turns red. Boil up for a minute, then let it settle, and decant or filter the liquid till clear. Test this liquid for glucose by the qualitative glucose tests. III. Into Dextrin and Maltose by Malt (Diastase Ferment). — Put some starch paste from II. into two little evaporating dishes. When nearly cool (not over a blood-heat) add to the first a few crushed grains of malt. To the second add a little extract of malt made by soaking some crushed nuilt in Avater and filtering the liquid. Let them stand a few minutes, and then test each for maltose with Fehling's solution. IV. Into Dextrin and Maltose by Saliva (Ptyalin Ferment). — Put starch paste into three clean evaporating dishes. To the first add a few drops of saliva. To the second add a little water solution of saliva, filtered. To the third add a little of the same solution boiled for a moment. Let all three stand some minutes, keeping them a little warm (not over blood heat at any time) by now and then holding them for a minute over the boiling starch solution of 11. Then test all three for maltose with Fehling's solution. Maltose will be present in Nos. 1 and 2, but will not appear in No. 3, LESSON IV. CANE SUGAR, MILK SUGAR, AND FERMENTATION. DI-SACCHARIDS OR SACCHAROSES. This important class of the carbohydrates stands half-way be- tween the starches and dextrins on the one hand, and the glu- coses on the other. They possess a definite formula (Ci2H220ia), and at least one of them, maltose, is derived from the breaking down of the more complex bodies. They all readily take up an extra molecule of water, and become converted into two mole- cules of glucose, the process being commonly called inversion, a name properly given only to the hydrolysis of cane sugar. They differ from the class of poly-saccharids in being crystalline and diffusible. It is harder to distinguish them from the glucoses, but neither cane sugar nor lactose ferment directly to alcohol, nor does cane sugar respond to the ordinary glucose reactions already described. CANE SUGAR. Saccharose^ Sucrose. Occurrence. — This important substance, by far the most prom- inent of all the carbohydrates, is found very widely distributed in the vegetable kingdom. It seems to be formed in the leaves, possibly in the same way that starch is, but probably either from starch itself or from derivatives of it, such as maltose or glucose. On a large scale it is obtained either from the juices of certain graminacese as the sugar cane and sorghum, or from roots such as the beet, or from the sap of trees like the palm and maple. It occurs also in all sweet fruits, in the nectar and juices of flowers, notably in the case of the cactus plant, and, in small quantities, in honey, manna, and other sweet vegetable products. In the latter instances, owing to the readiness with which it is CANE SUGAR. 37 inverted by acids as well as by ferments, it is always associated with more or less of the glucoses. Preparation.— The cane sugar of eoniinerce is, at present, almo.st entirely produced from either the sugar cane or the beet, small quantities only of sorghum, palm, or maple sugar ever coming into market. The sugar cane has the great advuntage over the beet in that its juice is both richer (14 to 20% of sugar) and purer. When beets were first introduced for this purpose, they contained only from 5 to 6% of sugar, and, though now they have been improved till they contain 15 to 1G%, still the juice is very impure and needs a very careful treatment. The process, in brief, consists of extracting the juice by crushing or diffusion, of purifying it by coagulating with lime and heat, skimming, and filtering, and finally of evapoi'ating it down nearly to dryness at as low a temperature as possible. The crude sugar must afterwards be refined by dissolving in water, filtering off the impurities very carefully with cloth and bone- black filters, and then evaporating in vacuum pans. Properties. — Cane sugar, from whatever source it is derived, is a white crystalline substance, of a specific gravity of 1.G06. It is sweet, extremely soluble in water, but practically insoluble in strong alcohol and in ether. It crystallizes readily from its solutions when pure, but this cryctallizing is easily hindered by numerous substances, both organic and inorganic, espe- cially by solutions of Isevulose or of invert sugar. It polar- izes to the right, [ajo being equal to -f 66.5". It is readilj' decomposed, into equal quantities of dextrose and laivulose, by long-continued boiling of an aqueous solution, by dilute acids, especially if heated, and by a variety of organized and unorgan- ized ferments. The resulting product polarizes decidedly to the left, the influence of the Isevulose being greater than that of dextrose, so that the plane of polarization is, by this operation, changed from right to left, or inverted, and hence the product is called invert sugar. When cane sugar is gently heated, it melts at about 160^ C. to a clear, almost colorless liquid, which solidifies on cooling to a clear glass, liable, however, to become cloudy and crystalline on gently warming again. This product is commonly known as 38 MEDICAL CHEMISTRY. barley sugar. On heating a little further, the color changes to yellow, and the sugar is convei'ted into dextrose and a substance known as li^vulosan, a gummy material, with a formula of CeHioOs, which polarizes slightly to the right, and changes readily into lyevulose on boiling with water, or when treated with weak acids, or by the prolonged action of j'east. When the mass is further heated it darkens in color, giving off gases, and changing to caramel, a name given to a group of strongly colored substances, soluble in water, which have the formula of sugar, less some molecules of water, e.g.^ CiaHisOg, CiaHiaOa, and so on. Finally, if the heating is continued far enough, all the hydrogen and oxygen are driven off, carrjang with them part of the carbon, and leaving behind a fine, slowly combustible coke equal in weight to about one-third of the original sugar. Tests. — These caramel products can also be easily formed from cane sugar by the action of concentrated sulphuric acid, which has at all times a great affinity for water. Dextrose is not so readily affected by this acid ; so this test serves to distinguish between the two substances. On the other hand dextrose is readily changed to caramel compounds by the action of caustic potash, as illustrated before in Moore's test. Pure cane sugar does not respond to the various glucose tests, nor will it undergo alcoholic fermentation until it is inverted by the invertin fer- ment of the yeast plant. Uses. — Cane sugar is used almost entirely for food — not only for its sweetening qualities, but also on account of its slight antiseptic properties, in jDreserves and syrups. It is somewhat used to strengthen as Avell as to SAveeten wines, and in an impure form it often serves as a source of alcohol. Some of it is used to produce caramel, which is valuable for its powerful coloring properties, as well as, to a slight extent, for its flavor ; and it has been enqiloyed in the manufacture of explosives. MILK SUGAR OR LACTOSE.— C12H22O,, + H.O. Occurrence and Preparation. — This sugar occurs in the milk of mammalia, and has also been found in small quantities in the fruit of one or two rare plants. The percentage in milk varies LACTOSE. 39 from d-0% in the case of sheep and cow's milk, up to G or 1:% or even higher in the case of human and mare's milk. It is usually obtained as a by-i>roduct, in the manufacture of cheese, by evaporating the whey and letting the sugar crystal- lize out on sticks or strings. This crude sugar can t hen be purified by recrystallizing. Properties.— Milk sugar occurs in more than one modifica- tion, two forms of the anhydride being known, besides the ordi- nary form, -which contains one molecule of water. The latter consists of large rhombic crystals, of a specific gravity of 1.53, and of a slightly sweetish taste. It is not very soluble in water, and hence gives a peculiar, rather gritty feeling between the teeth. It polarizes to the right about the same as anhydrous dextrose, [«]d at 20^" C. being equal to + 52.5°. This rotation is increased on inversion, the lactose being converted into equal quantities of dextrose and galactose. On heating dry lactose to 130' C, the molecule of water is driven off and we have one of the modifications of the anhydride. On further heating, it changes color and is gradually converted into lacto-caramel, a substance very similar to the caramel from cane sugar. Finally, a residue of carbon only is left. Tests. — Milk sugar responds readily to all the different glucose tests described in Lesson II. (The phenyl lactosazon which results from long-continued heating Avith phenyl hydrazin and acetate of soda can be distinguished from the glucose com- pound as it forms, on cooling, yellow, spherical masses of needle- shaped crystals.) It differs from glucose by not directly under- going alcoholic fermentation with yeast, and by fermenting to lactic acid when its solutions are exposed to the air. It is claimed by some authors that certain varieties of yeast will produce alco- hol from it, but probably in all cases it must first be inverted to glucose before the yeast will attack it. Uses. — It is a valuable article of food when in the form of milk. In a dry state it is used to some extent in pharmacy as a medium for taking drugs. It is sometimes used, in koumyss and similar products, as a source of alcohol. 40 MEDICAL CHEMISTRY. MALT SUGAR OR MALTOSE.— C.oHo^On + H2O. Occurrence and Preparation. — This sugar, although belonging to the di-saecharid group, is so very similar to dextrose that for a long while no distinction was made between the two. It is produced from starch by the action of the various amylo- lytic ferments alrearly described, diastase, ptyalin, and amylop- sin, and also from glycogen by the same ferments and probably in the liver. In all these cr.s^s, however, the maltose is changed into dextrose by jDrolonged action. It is also produced as an intermediate product in the conversion of starch into dextrose by means of acid, and hence occurs in small quantities in the raw glucose and glucose syrups. Properties. — Maltose forms white, needle shaped crystals, readily soluble in both water and alcohol. It polarizes strongly to the right, [oJd at 20° C. being equal to + 138°. It responds to all the ordinary glucose reactions, even, after long-continued warming, to the phenyl hydrazin test, where the phenyl malto- sazon finally sei^arates out on cooling into yellow, needle-shaped crystals, which do not radiate, like those from glucose, but re- main separate. By the action of yeast, maltose ferments easily and completely, and hence, besides its value in the digestion of cai'bohydrates, it is cliiefly important as a means for obtaining alcohol from starch. Starch as such is quite incapable of undergoing alcoholic f ermen tation until it is changed to maltose by the action of the diastase ferment of malt, or, in a few rare instances, by the ptyalin of the saliva. FERMENTATION EXPERIMENT. In this experiment the materials, proportions, and tempera- tures used are the same as those employed in the manufacture of corn whiskey. Indian corn is taken as the cheapest and most convenient source of starch, but with every eight pai'ts of corn is mixed one part of rj^e meal, not for the purposes of flavor, but because the salts and proteids contained in the rye enable the yeast to grow better. The mixed meal is "mashed," «.e., stirred to a stiff, smooth paste with boiling water, in order to hydrate all the starch present and let the diastase act ijromptly. It is MALT SUGAR OR MALTOSE. 41 then cooled to Go" C, and the crushed malt, equal in amount to the rye meal, is mixed in. The diastase attacks the starch almost at once, thinning down the mash by converting the paste into a solution of maltose. It is then further cooled to 24", when the yeast is added, and the fermentation begins almost immediatelj', and can be traced by tlie evolution of carbon dioxide. The fer- mentation is completed in from two to three days, by which time a " beer" has been formed containing 4 or 5% of alcohol. This is then concentrated to the desired degree by distillation. LABORATORY EXPERIMENTS. CANE SUGAR, MILK SUGAR, AND FERMENTATION. I. Cane Sugar or Sucrose.— 1st. Tesh- on dry sugar. (a) Place a little sugar in the smallest evaporating dish and heat very gently. Notice that the sugar gradually melts into a clear, yellowish liquid (when cold, called barley sugar), and afterward changes into glucose and into caramel. Let it cool, add a little water to it, and test the liquid fov the glucoses (invert sugar) by the qualitative glucose tests. {b) Put a little sugar into one test-tube and some dry glucose into another. To each add a little common H2SO4. Notice that the sugar blackens at once, while the dexti'ose is not affected for some little time. (c) Put a little sugar into one test-tube and some dry glucose into another. To each add a little KOH ; heat, and notice that only the dextrose changes color. 2d. Dissolve some sugar in laafer, and test the solution. (a) Try it with Fehling't:- solution ; notice that it does not re- sjjond. (b) Boil tliesugarsolution first and then test ; it responds either not at all or only slightly. (c) Add to the solution a drop of II^SOj dil. or of IICl dil., and just raise it to the boiling-jwint. Now test with Fehling's solu- tion and there will be a strong reaction for glucose (invert sugar). II. Milk-Sugar or Lactose.— Taste it; dissolve some in water; test this solution with Moore's and Fehling's tests. 42 MEDICAL CHEMISTRY. III. Fermentation Experiment. — Fill the saucepan one-half full of water, boil it well, remove the flame, and at once stir into it all the corn-meal and the rye flour. Stir it thoroughly, boiling all the time, till all the lumps are broken up and the " mash" is smooth and stiff. Cool to 65° C, and then add the malt, ground up, and with the husks sifted out. Notice how the malt at once "cuts" the mash, changing the starch into maltose. Stir and cool to 24" C, preparing the bent deli very -tube while it cools. Pour it into the bottle, add the yeast, thinned with a little water, and finally fit in the cork and delivery-tube. The end of the latter must dip Fig. 3. into lime-water, Ca(0H)2, placed in a conical glass. Cover this with a piece of filter-paper, with a hole through which the delivery-tube can pass ; and at intervals during the rest of the afternoon, and during the next day, notice the progress of the fermentation. The delivery-tube mentioned above is a quarter-inch tube of soft glass some fifteen to eighteen inches long, which the student is expected to bend into shape in the Bunsen flame, or, better, in aflat, open gas jet. It should be bent first at a right angle, some three inches from the end that is to fit into the cork, and some four or five inches farther on a second bend should be made, through an angle of 45" or so, to lead the gas down into the lime-water. lesso:n' v. ALCOHOL, CARBON DIOXIDE, AND YEAST. ALCOHOL; ETHYL ALCOHOL.— C2H5OH. History. — The name alcohol in chemistry has been given to a large and important series of organic compounds formed Ijy the combination of hydroxyl, OH, with basic organic radicals, and corresponding exactly with the inorganic compounds known as the metallic hydi'ates or hydrolides. The hydrate of ethyl, CzHe, or ordinary ethyl alcohol, which is the only member of the series that interests us here, has been known in a dilute and impure state, as wine and beer, since the earliest ages. It was not possible to obtain it in at all a pure form until after the inventionof distilling by the early alchemists. The "spirits of wine," as it was then called, Avas early recognized as a powerful medicine, and it was as a medicine that the use of distilled liquors first spread over the civilized world. By repeat- edly rectifying over wood ashes or lime, the early alchemists were able to obtain even absolute alcohol in a fairly pure condition. Preparation. — Alcohol can be made from purely inorganic substances, as, e.g., from acetylene gas originally derived from the combination of carbon and hydrogen. In practice, however, it is exclusively prepared by the alcoholic fermentation of certain carbohydrates, through the agency of the common yeast plant, Saccharomyces cerevisise. This plant, first described by Van Leeuwenhoek, consists of small oval cells, varying in length from .008 to .014 nnn. It is usually found in bunches or aggregations known as top yeast, be- cause the bubbles of gas catching in them raise them to the sur- face. Sometimes, however, Avhen the fermentation takes place at a very low temperature, the yeast cells break off from each other as fast as they form, and the individual cells settle down- ward, making what is known as bottom yeast. Under ordinary 44 MEDICAL CHEMISTRY. circumstances yeast grows best at a temperature of from 23° to 24° C, though it still hves and multiphes at temj)ex'atures con- siderably above and below this. It feeds mainly on certain cai'bohydrates, namely maltose and the glucoses, which it converts into alcohol and carbon dioxide, according to the formulae : For maltose, CiiHs^On + H2O = 4 C2H5OH + 400^ For glucose, CgHioOg = 2C2H6OH + 2CO2. Besides carbohydrates, the yeast needs small quantities of fats, of nitrogenous material, and of mineral salts. Also, besides alco- hol and cai'bon dioxide and its own substance, it produces small quantities of the higher alcohols, of organic acids, of glycerin, and of other organic compounds. The quantity of alcohol in a liquid that has undergone fex'men- tation rarely, under the most favorable circumstances, amounts to 10^, and usually is not much more than half that amount. By simple distillation, it is possible to concentrate the alcohol to any desired amount up to 93$^ or 9i%. Above this point it is neces- sary to add to the still some hygroscopic substance, hke quick- lime or chloride of calcium, to absorb the rest of the water. Properties. — When pure it is a colorless volatile liquid, of a pleasant smell and very burning taste. It has a specific gravity at 15° C. of .798, and, as this increases regularly with the quantity of water mixed with it, we can readily, if we know the density, determine the percentage of alcohol. It boils at 78.3° C, it burns readily with a blue flame, and its vapors form explosive mixtures with air. Its freezing point has not been determined. It has a strong affinity for water, absorbing it from the air, or from sub- stances it may be in contact with. Hence alcohol is largely used as a dehydrating, hardening, and preserving medium, and hence also comes the burning sensation when strong alcohol is brought in contact with the mucous membranes of the body. It is a curious fact that when alcohol and water are mixed together a perceptible shrinkage occurs. Uses. — Alcohol is principally used as a stimulant, being con- sumed in enormous quantities under the form of both distilled and fermented beverages. It is exceedingly valuable as a medi- cine. It is largely used in the arts as a solvent, and also in small alcohol; ethyl alcohol. 45 amounts for the preparation of chloroform, iodoform, and some other organic compounds. Tests.— The tests for alcohol are of considerable importance. 1st. The Iodoform Tes^.— Iodoform, CHI3, a compound of iodine and the organic radical methenyl, is formed by the action of iodine and potassic hydrate on alcohol, and also on acetone, aldehyde, and some other organ iccomijound.s. The reaction isas follows : C2H0OH + 4IQ + GKOH = CHI3 + KCHO., + 5KI + 11,0 Iodoform Potassium formate The iodoform precipitates out in the form of yellow, six-sided crystals. These crystals first appear as plain, flat hexagons, but, after standing a little, modifications occur on each of the six sides, forming regular star-shaped figures of much beauty. Iodoform is very heavy, being almost entirely composed of iodine. It is soluble in alcohol, very slightly soluble in water, has a peculiar smell, and is very largely used in surgery as a mild antiseptic. This test is extremely delicate, but reacts with acetone and aldehyde as well as with alcohol. 2d. The Molyhdie Achl IZV.s-^.— In this test we use a solution of molybdic anhydride, M0O3, in sulphuric acid. The alcohol takes an atom of oxygen from the compound, changing it to deep blue suboxide of molybdenum, M0O2, and itself being converted into aldehyde, a volatile liquid of unpleasant odor. The reaction is as follows : C2H5OH + MoO-, rrr M0O2 + C^H.O + H2O Aldehyde This tost is quite delicate, Init reacts with other strongly reduc- ing organic substances besides alcohol. 3d. Chromic-Acul Test. — This also depends upon the reduction of a chemical substance by the alcohol, which is oxydized to aldehyde. In dichromato of potash, KoCr.OT, or dichromic acid, HsCroOi, which may result from its mixture with hydrochloric acid, the oxide of chromium acts as an acid radical. On reduction, how- ever, the metal itself is set free, and this combines with the hy- drochloric acid to form a green chloride of chromium. Thus: 46 MEDICAL CHEMISTRY. KaCr.O, + 3C.2H5OH + 8HC1 = Cr^Cle + 3C,H40 + 7H2O + 3KC1 This test is not as delicate as the preceding ones, and reacts with most of tlie ordinary reducing agents, hydrogen, sulphur- ous acid, glucose, and others. 4th. Acetic-Ether Test.— In this test, by the action of the acetic acid on alcohol, we produce a so-called compound ether, i.e., an oxygen salt of an organic radical; in this case, an acetate of ethyl, or acetic ether. The reaction is precisely similar to the formation of potassic nitrate by the action of nitric acid onpotassic hydrate. Thus, KOH + HNO3 = KNO3 + H2O Potassic Hydrate Nitric Acid Potassic Nitrate. C2H5OH + H.C2H3O2 = C^Hs.C.HaO^ + H.O Ethyl Alcohol Acetic Acid Ethyl Acetate or Acetic Ether The strong sulphuric acid is added partly to set free acetic acid from the acetate of soda, but chiefly to assist the reaction by absorbing the water liberated. Acetic ether has a particulai'ly pleasant, fragrant smell, not unlike that of bananas ; it occurs in minute quantities in the flavoring elements of certain fruits, and also in the bouquet of old wines and liquors. LABORATORY EXPERIMENTS. ALCOHOL, CARBON DIOXIDE, AND YEAST. I. Alcohol. — CiHsOH. — Decant off the top of the fermented liquor, from the last lesson, into a flask. Add apiece or two of pumieestone, fit in the distilling-tube, and distil gently half the liquid into a flask, small beaker, or test-tube. Taste the distil- late and test it for alcohol as follows : 1st. Iodoform Test. — Add to a test-tube one inch of the distillate and five or six drops of KOH. Warm very gently, add a little iodine till it is yellow, and then, carefully, one or two drops of KOH till the yellow color jnst fades. Let it stand a few minutes, mix it up gently, notice the eharaeteristie odor of iodoform, and examine the crystals under the microscope. TESTS FOR ALCOHOL. 47 2d. 3Iolybdic Acid Test. — Put in a test-tube half an inch of molj'btlic acid solution. Add two or three drops of tlie distillate ; notice the blue color, due to M0O2. 3d. Chromic-Acid Test. — Fill a test-tube one third to one-half full of the distillate, add two or three droi)s of potassic dichro- mate, K.iCr207, and two or three drops of HCl cone. Boil ; notice that the liquid turns green. — N.B. This test is not as delicate as tests 1st and 2d. If it does not work well with the distillate, re- peat it with a little alcohol from the shelf. Make the following test with alcohol from the shelf : * Acetic Ether T'est. — Fill a flask one-third full of alcohol, add one- fourth as much sodic acetate, NaCaHaOa, and then run in, very carefully, common H2SO4, shaking gently till the liquid begins to boil. Notice the pleasant fragrant odor of acetic ether. II. Carbon Dioxide. — CO..— Take the conical glass of Ca (OH);!, exposed to the gas from the fermentation, and filter off the white calcic carbonate, CaCOa, in a small funnel. Throw away the fil- trate, but set the funnel over a small test-tube, and on to the filter paper pour a few drojis of IICl dilute. Notice the effervescence that results, showing the iiresence of CO2. Boil for a minute the solution of calcic chloride that passes through into the test-tube, to drive off the CO2, add to it some amnionic hydrate, NH4OH, till it is alkaline to red litmus pai)er, and then a few drops of am- nionic oxalate, (NHi)2C20i. The white ppt. of calcicoxalate that results shows calcium, Ca. III. Yeast. — With the platinum wire pick out a little yeast from the to]) of the li(juid in the fermentation bottle, or from the sides of the bottle, where the top of the li(]uid has been. Spread this out on a slide with a drop of water, and examine it under the microscope with both low and high powers, both without and with the addition of a little fuchsin. Notice the yeast cells, both single and in chains and masses. Also take a drop of the liquid from the fermentation bottle, and, examining carefully with the high power, notice the great number and the large variety of bacteria present. * When heatinf^ solutions containing much alooliol, or when usinp volatile liquids, especially gasolene and eiher, great care must be taken to prevent the vapors from igniting. 48 MEDICAL CHEMISTRY. N.B. — The distilling-tube mentioned in the first part of the above lesson is to be prepai*ed by the student from a piece of quarter-inch soft glass tubing some thirty inches long. When properly made and fitted to the flask it should have four bends in it, as follows : About an inch from the cork it should bend up- ward on a gradual incline, so as to give vapors that condense readily a chance run to back into the flask. Then, near the Fig. 4. middle of the tube, it should be bent downward at a similar angle. On this part are hung, during the distillation, pieces of filter paper kept wet by a constant stream of water from the wash bottles. About four or five inches from the end of the glass it should be Vjent upward for half an inch or so, so as to give a drip for the wash water ; and then the tube is bent down perpen- dicularly to let the distillate drop down into a beaker, flask, or test-tube below. Plate na. 5. Yeast, k250. Flo. 6. Bactoria, x SOO. PART II. THE FATS. LESSON VL FATS AND SOAPS. THE FATS AND FIXED OILS. These substances difiei* from the carboliydrates and the pro- teids in that both their composition and their chemical struc- ture are well understood. They belong to the conn)ounds men- tioned on the last page as compound ethers, i.e., oxygen salts of an organic radical, and, though of varied composition, they have this in common: they are all salts of the one triatomic radi- cal propenyl, C3H5, with the large class of acids known as the fatty acids. Occurrence. — The ivi^ occur hi large quantities and in great variety in both animals and plants. They seem, in most cases, to be present as a store of highly-oxidizable food. In animals they occur to a small extent in the fluids of the body — blood, sweat, lymph, etc. — and also, in the form of an emulsion, in milk. They are present in almost all the tissues of the body, and are found as special deposits in large quantities in various parts of the body in the cells of the adipose tissue. They are stored up in plants chiefly round the embryo in seeds and nuts, where they take the place, more or less completely, of starch. Preparation.— The animal fats are extracted from the tissue in several ways. The simplest method, and, until late years, the only one practised on a large scale, is to try it out by heating it until the other matter in the cells shrivels up and sets the fat free. The disadvantage in this method is that, no matter liow carefully it is managed, the temperature must be raised so liigh that some decomposition takes place, seriously injuring the flavor if not the appearance of the fat. Some fats, as palm oil, are extracted by boiling the material with Avater, when the oil rises to the surface. In other cases they are extracted by pressure. 52 MEDICAL CHEMISTRY, When the fats are valuable, they are sometimes even dissolved out by some solvent, such as carbon disulphide. A great improvement in the extraction of ordinary fats was in- troduced by Mege Mouriez, of Paris, about twenty years ago, and consists of the hashing the adipose tissue extremely fine and then heating it gently to a temperature just above the melting-point of the fats. In this way the cells are broken up mechanically, and the melted fat runs out without any trouble, giving a par- ticularly pure article. This process is the basis of the oleomar- garin industry, and has been applied to the extraction of fat from other sources. Composition. — The chemical nature of these bodies was first determined by Chevreuil, about 1820, who found that most of the common fats and oils, no matter what their consistence, were composed of olein (liquid) associated with stearin, margarin, and palmitin. Heintz afterwards eliminated margarin, showing it to be a mixtvire of stearin and palmitin. The ordinary animal fats contain these three substances and no others. In butter we find mixed with them small propor- tions of other fats, which give it peculiar properties, and in many vegetable oils, linseed and castor oils, for instance, we find quite large quantities of other similar compounds njixed with them. But in most cases these three substances so far predomi- nate that the physical properties of the fat depend upon the varying proportions of the hard stearin, the fluid olein, or the soft, semi-solid palmitin present. These fats are, as already mentioned, salts of the base propenyl, C3H5, with three molecules each of stearic, oleic, and palmitic acids respectively. Thus the formula for stearin is C3H6.(Cj8H3602)3, dcrlvcd from C3H5 and three molecules of stearic acid, H.C18H3SO2. In percentage composition the carbon predominates, with hydrogen and oxygen in smaller proportions; stearin, for instance, contains carbon HSfo, hydrogen 13^, and oxygen 10%. As seen by the formula there is less oxygen, and hence greater potential energy, in these than in the carbohydrates. Properties. — The fats all weigh less than water, their specific gravity varying from .910 to .970 or so. AVhen pure they are color- less or faint yellow, and generally have but little taste or smell. THE FATS. 53 They are viscous and unctuous to the touch, leaving a grease spot on paper, and not evaporating below a decomposing tem- perature. With the exception, i)erhaps, of castor oil, they have no action on polarized light. They are quite insoluble in water, but dissolve more or less readily in boiling alcohol. They dissolve freely in many volatile organic liquids, like the light petroleum and coal-tar products, ether, carbon disulphide, chloroform, and others. In bulk they are not, as a rule, specially infiaunaable, but burn freely in small quantities, e.g., with a wick. They readily decompose, when heated dry, into a variety of more or less offensively smelling bodies; this also occurs when they are treated with strong sul- phuric acid or other dehydrating agents. When acted on by superheated steam or by alkalies and dilute acids they undergo saponification, i.e., they change to glycerin and either fatty acid or soaj:). On long-continued exposure to the air, some of them, the so-called drying oils, are gradually oxidized into more solid compounds ; while others, vinless exceedingly ijure, undergo a process of fermentation and are more or less decomposed into fatty acids and other compounds. Uses. — The fats are among the important constituents of animal food, although a good deal of the fat in the body is undoubtedly formed in the system from carbohydrates and proteids. They serve as fuel, being oxidized to carbon dioxide and water, and, owing to their small percentage of oxygen, they develop a large amount of energy. Often the fat must be added to the food, be- fore eating, in the form of butter, suet, and oils; this is generally the case with vegetable food. Animal foods are, as a rule, richer in fat, ordinary meat containing from 5 to 10/'^, milk 3 to 45?, eggs 12r/, cheese 8 to 30$?, and butter 85 to 90^. Besides as food, some of the fats are used in medicine for certain special properties they possess, e.g., ca.stor oil and cod-liver oil. In pharmacy also they are largely employed as ointments and salves, and as a medium for other and more active remedies. Enormous quantities of fat are consumed in the manufacture of soap ; the oils are extremely useful for lubricating purposes, and as vehicles for paint, and, though now largely superseded by gas and petroleum products, for artificial illumination. 54 MEDICAL CHEMISTRY. The waxes are similar to the fats in being compound ethers of the fatty acids. These acids, however, are not combined with propenyl, but with cetyl, C10H33, ceryl, CotHss, myrieyl, CsoHei, and one or two similar radicals. SOAP, Definition. — A soap may be defined as a metallic salt of a fatty acid. This distinguishes it from a fat, which, as we have seen, is a salt of a fatty acid with propenyl, and from glycerin which is the hydrate of propenyl. Although the number of pos- sible soaps is very large, the only ones commonly known and in general use are those of the alkaline metals, sodium and i^o- tassium. Preparation. — Soap is generally made by boiling fat with a caustic alkali, either with potash, when the soft or potash soap is produced, from which the hard soap must be prepared by the aid of salt, or, as is now more generally the case, with soda. Ordinarily this process takes a good deal of time, and, to hasten the operation, when but small quantities are to be made, the alkali is sometimes dissolved in alcohol — as, for instance, in Les- son VII. It is possible, however, when using just the right pro- portions of castor oil and very concentrated sodic hydi-ate, to make a hard castor-oil soap, ricinoleate of soda, in a very few minutes, without much heating. When a fat is saponified in this way, a very simple reaction takes place, the metal of the alkali changing places with the pro- penyl of the fat. As propenyl has three bonds, however, and potassium or sodium has only one, we must have three potassium atoms present for every molecule of the fat. CaHaCCnHssOa + 3K0H = SKCBHasO^ + C3H,(OH)3 Propenyl Stearate Potassic Potassic Stearate Propenyl Hydrate or Stearin Hydrate or Soap or Glycerin These potash soaps are soft and semi-fluid at ordinary tempera- tures, and hence are called soft soaps. If sodic hydrate were used instead of the potash, we should form a soda or hard soap, like the ordinary toilet or cake soap. This can also be prepared from the soft soap by the addition of common salt, NaCl. Thus, KChHssOs + NaCl = NaCiBHaBOs + KCl Soft Soap-. Hard Soap SOAP. 55 Properties. — Both of these varieties of soap dissolve in warm and cold water, and in alcohol. When dissolved in large quan- tities of water, they have rather a turbid appearance and an alkaline reaction, and seem to be converted, more or less, into free alkali and an insoluble aciil salt. This proi^erty, it is be- lieved, enables them to act as cleansing agents ; for the free alkali attacks the greasy dirt on hands or clothing, dissolving the fatty matter and setting the rest free, while the insoluble salt forms a slipijery lather, which involves and carries away with itself the dirt and gritty matter. There is always present, also, in commei'- cial soaps, a certain quantity of free alkali, which contributes to the cleansing effect. They always contain Avater. from 20 to over 80,'i^, as well as salts, coloring and scenting materials, and often solid matters— sand, emery, etc. — either for special purposes or for adulteration. On the addition of acid, they decompose, yielding free fatty acids, according to the following reaction: KC..H35O0 + HCl = HC.HasO^ + KCl Soft Soap Stearic Acid. These ordinary soda and potash soaps are the ones so largely used for washing and cleansing purposes. By adding metallic salts to their solutions Ave can form insoluble soaps Avith almost eA'ery metal in the list of elements. Several of these compounds Avere prepared in the lesson, and in each ease the metal is simply substituted for the potassium or sodium of the soap, as in the folloAving reactions : For silver, AgNOa + KC..H.5O. = AgC,.H3.0. + KNO3 and for calcium, CaCU + 2KC,6H3502 = Ca(C,,H350,h+2KCl Two of these soaps deserve a little notice : The lead soap is prepared sometimes in pharmacy for use as a plaster, not, hoAV- ever, as in this lesson, but by boiling together oxide of lead Avith Avater and oil. The calcium or lime soap, generally mixed with the magnesium soap, is the compound formed Avhen soap is used in hard or calcareous water. The lime in the Avater at once forms this sticky, insoluble precipitate, nor is it possible to get a satisfactory lather until the lime has taken up its full share 56 MEDICAL CHEMISTRY. of soap. By adding, however, a certain amount of carbonate of soda to the water, the hnie will be precipitated or neutrah'zed and the lather forms at once. Emulsiox. — Before finishing- the lesson, a word or two of ex- planation should be given about this peculiar condition. A fluid or semi-fluid substance is said to be emulsified when its particles are finely divided and refuse to coalesce. When this happens, it is supposed that each little particle is coated with a thin layer of some other body, which is sufficient to prevent a true contact between the globules. This is done, for instance, when mercury is rubbed up in a mortar with lard, forming a gray ointment, with minute globules of mercury kept apart by a coating of fat. In oils and melted fats this occurs best when they are shaken up with solutions of soap, or, which amounts to the same thing, of alkalies or alkaline salts, and also of various organic compounds, such as proteids, gums, etc. Sometimes as in milk, both alkalies and proteids unite to make a very perfect emulsion. On examining a drop under the microscope, the little globules of fat can be seen, perfectly distinct, of various shapes and sizes, and quite separated from each other. LABORATORY EXPERIMENTS, FATS AND SOAPS. I. Beef Fat. — Cut up the beef fat into small pieces, i")lace it in the saucepan, and heat it carefully over the flame until the en- velopes shrivel up and the fat melts out. Do not heat too hot, and be very careful not to let any water get into the saucepan during the operation. When all the tallow is free, fdter it through dry filter paper on to the agate plate, and let it cool for an houj". Then put a little shaving of this fat into the "melting- point tulje," tie the tube to the thermometer so that the lump of fat is level with the bulb of the instrument, and i^lace both together in a beaker of water, not letting the water enter the tube. Heat very gently, and notice the temi:)erature at which the tallow begins to melt, usually between 40° and 45° C. SOAPS. 57 II. Soaps.— Dissolve soft or potash soap in warm water in a beaker, and test the sokition as follows : 1st. Put in a test-tube half an inch of solution, add water till half full, and shake. Notice the strong lather. 2d. Put in a test-tube half an inch of solution, add a little calcic chloride, CaCla, and then water. Shake = no lather, but a white curdy ppt. of lime soap. 3d. Put in a test-tube half an inch of solution and a little CaCla. Add half an inch of sodic carbonate, XaaCOa (washing soda), and Avater, and shake — a lather, as in 1st. The soda has neutralized the effects of the lime. 4th. Fill a test-tube half full of solution, and add a few drops of HCl cone. Notice the separation of fatty acids. Heat gently ; notice that the acids will float like oil on the top of the liquid. 5th. Make a series of metallic compounds (soaps) by putting some soap solution into 8 test-tubes and adding separately a few drops of the following reagents : (a) Baric chloride, BaCU = a white Ba soap. (&) Magnesic sulphate, MgS04 = a white Mg soap. (c) Ferrous sulphate, in solution, FeS04 = a greenish-white ferrous soap. (rf) Ferric chloride, FesCla = a brown ferric soap. (e) Plumbic acetate, Pb(C2H302)2 = a white Pb soap (lead plaster). (/) Cupric sulphate, CUSO4 = a blue Cu soap. . {g) Argentic nitrate, AgNOs = a white Ag soap. {h) Mercuric chloride, HgCla = a white mercuric soap. N.B. — If the soft soap used in these tests contains much free caustic alkali, the argentic and mercuric pi)ts. will be colored gray and red respectively from the presence of AgOH and Hg(0H)2. To the rest of the solution in the beaker add a quantity of dry sodic chloride, NaCl. Boil and notice the formation of hard, or soda, soap. III. Formation of Hard Soap. — Make some soap in the follow- ing UianntT : To the castor oil, in a small evaporating dish, add the strong solution of scdic hydrate, NaOH, and stir thoroughly with a glass rod. Notice that at first this forms simply an emulsion. 58 MEDICAL CHEMISTRY. but that gradually this emulsion gets thicker and thicker. Warm it very gently on a water-bath (not letting it melt), stir- ring it constantly all the time, and in a few minutes the mixture will get quite stiff and firm. Wait and stir a little longer and it will form a solid, hard soap. Dissolv^e this soaj) in a beaker with hot water, and with the solution make the tests 1st to 4th under Section II. and also some or all of the tests under test 5th. Notice that this soap reacts exactly the same as the soft soap. IV. Pork Fat,— Scrape the saucepan clean, fill it two-thirds full of water, and boil. Tie up the pork fat in muslin, place it in the boiling water, and press it well with a rod. The lard soaks through and rises to the top. Filter through a wet filter paper, and notice that the lard does not pass through. Let some of the lard cool and notice how much purer it is than the tallow obtained from I. Shake some of this lard, while melted, with warm water in a test-tube ; notice how it rises to the top again. To the same mixture add half an inch of KOH ; notice that the lard forms a white emulsion. Note.— The " melting-point tube " used in tlie first part of this lesson is a piece of quarter-inch glass tubing some three or four inches long, drawn out into a blunt point and closed at one end. The other end is left open, and the little sliver of hard tat is dropped or pushed down it till near the bottom. LESSON VII. BUTTER, OLEOMARGARIN, GLYCERIN, AND OILS. BUTTER. Occurrence.— This fat is found in the milk of the nmnniiaha to the amt)unt of from l:^,'? to 5%. It oecui'S, not dissolved in the Hquid, but suspended in it in the form of fine round globules, kept in an emulsified condition l>y, probably, the casein present. Preparation. — It is extracted first as cream, and then, in the process of churning, the globules coalesce and the solid fat sepa- rates more or less thoroughly from the other constituents of the milk. As it comes to market, butter rarely contains more than 80^ or 85;? of fat; the rest is principally water, with some proteids and lactose from buttermilk still remaining in it, and with more or less salt and sometimes saltjjetre, to flavor and jireserve it. It is also generally colored more or less with some harmless vegetable comjaound. The presence of buttermilk is very objectional)le, for it begins to decompose almost immediately, and sets up fer- mentation in the butter itself. Oleomargarin. — Of the various fats used as substitutes for l)ut- ter, the most imijortant by far is that prepared by the so-called oleomargarin process. The fat used for this purpose is generally that contained in the intestinal folds, chiefly the omentum and mesentery, in beef cattle. It is carefully sti-ipped from the fresh carcass, washed, chilled, and hashed exceedingly fine. It is then melted at a temperature of 50° or 51° C, and the liquid fat, drawn clear from any scrap, is allowed to stand for two or three days in small vats at a temperature (about 27° C.) at which but- ter is just liquid. The hai'der fats, stearin and some palmitin, separate in tlie form of fine crystals. The liquid is pressed from these, and runs away as a thin yellow oil which solidities on cool- ing to crude oleomargarin (butter- or oleomargarin-oil). 60 MEDICAL CHEMISTRY. To turn this into a very good substitute for butter it is only necessary to churn it with some milk so that it can absorb some of the butter taste, to add the proper amount of coloring matter, and to chill it very rapidly. It then can be salted and packed like ordinary butter. This material, as it comes into market, presents two very decided advantages over butter ; for it is not only much cheaper, but, owing to the absence both of butter- milk and also of the peculiar butter fats mentioned below, it has much better keeping qualities. In flavor it ranks well with sec- ond-class butter, but hardly comes up to the standard of the very finest grades. Composition. — Butter fat is much more comi)lex than the other animal or even vegetable fats. Besides the ordinary stearin, palmitin, and olein, which compose over 90^ of its weight, there are some eight or ten well-recognized compounds to be found in it. Among these we have the fats, myristin and arachidin ; the so-called butter fats, caprin, caprylin, caproin, and butyrin ; the propenyl compounds of acetic and formic acid, and the pecu- liar substance known as cholesterin. The butter fats, which are the most important of these, are propenyl salts of fatty acids with comparatively low molecular weights, e.g. of butyric acid, H.C4H702; normal caproic acid, H.CeHnOs; normal caprylic acid, H.CbHi502; and capric acid, H.CioHigOa. These com- pounds, and especially the first of them, butyrin,/ give the peculiar taste and odor to butter. They are quite liable to de- compose, and to develop their respective acids. The acids themselves have some characteristic properties. They have a strong rancid smell and taste, easily recognized as occurring in decomposing butter. They ai'e light, volatile liquids, which dissolve more or less in water, and can be dis- tilled with the steam by boiling a solution containing them. In these respects they differ very materially from the odorless, in- soluble, and non- volatile, solid or nearly solid fatty acids from the ordinary fats. Hence to determine the presence and even the percentage of butter in a sample of fat it is only necessary to obtain the fatty acids and to distil them, and then to notice the presence and the quantity of the butter acids in the distillate. In our lesson the process is conducted as it is in practice in the BUTTER ACIDS. 61 analytical lal)oi-atory. To obtain fatty acids, as in Lesson VI., we must add a strong mineral acid to soap. Hence we first con- vert the butter into soap by Ijoiling it with an alcoliolic solution of potash, and then, after driving off the last traces of alcohol, we decoiupo.se the soap with dilute sulphuric acid, and distil off the volatile fatty acids. If these are present, the distillate will have a rancid smell and taste, and be acid to test paper. These butter acids will form salts with bases, and with alcohol and .strong sul- phuric acid the butyric acid acts just the same as acetic acid did in the last test in Le.sson V., i.e., it forms ethyl butyrate, or butyric ether. This latter, which has a pleasant, fragrant, pineapple odor, occui-s naturally in many fruits, and in liciuors, especially when old and well matured, and is prepared quite largely as a flavoring agent for syrups and beverages. This odor of butyric ether is obtained more or less whenever butter is saponified in the presence of alcohol, and hence its pi-esenee on boiling a sample of fat with an alcoholic solution of potash is true evidence of the presence of butter. GLYCERIN. Fropenyl Hydrate ; Glycerol. — C3H6(OH)3. Pi'eparation. — This substance, discovered in 1779, by Scheele, is formed whenever a fat is saponified, i.e.., decomposed either into soap or into a fatty acid. Although produced in large quantities in the manufacture of soap by boiling with alkali, it has been found troublesome to separate this glycerin from the alkali and other impurities in a merchantable form. So it is usually prepared as a by-product in the manufacture of stearic and other fatty acids, by treating fat either with diluted sul- phuric acid, or, better, with superheated water or steam. The latter reaction is as follows : CalUlC.H.'i.O,)^ -f 3H.,0 = 3H. C.H.oO^ + C3H5(OH)3 After the removal of the fatty acids, the water is evaporated, and the glycerin purified by distillation and by crystallization. Glycerin is also produced in small quantities in alcoholic fer- mentation, and accordingly is present in all fermented liquors. Properties. — "When pure, it is a clear, colorless, thick li(iuid, with no odor and a sweet taste. It dissolves readilv in water and 62 MEDICAL CHEMISTEY. alcohol, and absorbs moisture from the air. It solidifies at — 40° C. to a gummy mass; but, even at 0° C, crystals will slowly form if the liquid is kept quiet for a long time, and will form at once on the addition of crystals previously prepared. It boils at 290° C. and evaporates at low^er temperatures, though it is practically non-volatile at the temperature of the atmosphere. It has a specific gravity at 15" C. of 1.263. In composition glycerin is a triatomie alcohol, being a hydrate of the triad organic radical, propenyl. It ignites at 150° C. and burns readily with a blue flame. It decomposes when heated with dehydrating agents, as, for instance, sulphuric acid, into acrolein and similar compounds. It does not undergo the ordi- nary alcoholic fermentation with the yeast plant, and is often added as a sweetening to wines and liquors when it is undesirable to have any further fermentation. It can, however, be fer- mented, probably by certain kinds of bacteria, and alcohol is one of the products. By the combined action of strong nitric and sulphuric acids it is converted into nitroglycerin. Uses. — Glycerin often takes the place of sugar as a sweetening agent and preservative in sja-ups and beverages of all sorts. It seems to be digested readily. It is also quite largely used as a solvent especially where there is danger of decomposition. Thus, it is used in extracting ferments, in making ointments and salves, and in dissolving delicate coloring matters, and scenting and flavoring matters, from their sources. It is also largely used, on account of its physical properties, as a lubricant, for sealing gas-holders, for filling meters, for mixing with clay, paints, etc., to keep them moist, and for several similar purposes. THE OILS. The oils differ from the ordinarj"- fats in that they contain more olein and less palmitin and stearin, and hence are fluid at the temperature of the atmosphere. We have selected three of the most prominent of them to serve as examples — Castor Oil. — This is a vegetable oil, composing nearly half the weight of the seeds of Ricinus communis. This plant came orig- inally from the East Indies, but is now largely cultivated in hot THE OILS. G3 climates for its oil, and in more moderate climates as an orna- ment. The best oil is then obtained by pressing the seeds cold, and inferior grades are obtained by heating and re-pressing the resi- dues. It is refined by filtering, bone-black being often used. The pure oil is a transparent, colorless or faintly greenish, thick liquid, with a slight smell and rather a nauseous taste. It has a high specific gravity, .950 to .970 at 15" C, and is exti'emely viscous. It solidifies at —18' C. It can easily be distinguished from other oils by being readily soluble in alcohol, and by not dissolving in the light petroleum products. Thus, when mixed with gasolene, it seems to dissolve about its own bulk of that liquid, but the mixture is insoluble in an excess of solvent. Besides palmitin, with some stearin andolein, it contains a con- siderable amount of the fat known as ricinolein, derived from ricinoleic acid, H.CibHaaOs. This fat is readily saponified, even in the cold, by strong caustic alkalies, and the hard soap formed in the third part of Lesson VI. was principally comjiosed of ricinoleate of soda. Castor oil has important medical properties, and in its purest form it is widely used as a pui'gative. It is largely employed for lubricating purposes, and for soapmaking, and also in dyeing and calico printing. It is adulterated with poppy, lard, cocoanut and other oils, and also with a thicker compound, blow oil, made ])v partially oxidizing rape and cotton-seed oils. It gives a characteristic color with suli)huric acid. Olive Oil.— This is extracted from the fruit of the olive-tree, either by pressing or by extraction with some solvent lil\e carbon disuii)hide. It varies enormously in quality, according to the variety, ripeness, and condition of the fruit, the temperature and severity of the pressing, and the subsecjuent treatment of the oil. The finest grades come from the shores of the Mediterranean. Pure olive oil has a faint yellow color, slightly tinged with green. It is almost odorless, and has a pleasant taste. It is neither as dense (sp. gr., .914 to .918) nor as viscous as castor oil. It dis.solves readily in light petroleum and coal-tar compounds, as well as chloroform, carbon disulphide, and ether, but is only sparingly soluble in alcohol. It consists almost entirely of oleia, 6-i MEDICAL CHEMISTRY. mixed with stearin and palniitin, with traces of araehidin, cholesterin, free oleic acid, and some albuminous matter. Owing to the presence of the latter, it gradually becomes rancid in the air, though it does not thicken or oxidize like the so-called " dry- ing ■' oils. Olive oil is used largely as a food, and the finer grades, used for salad oil, etc., are prepared with the greatest care, and are obtained pure with much difficulty. Inferior qualities are used for mak- ing soap, for illumination, and other minor purposes. The price of good olive oil is so high that it is enormously adulterated, principally with cotton-seed oil, but also with lard, poppy, rape, and even purified fish or hydrocarbon oils. With a drop of sulphuric acid it turns brown at the centre, but around the drop of acid can generally be distinguished a peculiar and characteristic shade of olive-green. Cod-Liver Oil. — This is obtained from the livers of codfish. The oil is extracted by gentle heat, and by pressure, and the re- sulting oil is of various grades, distinguished by color and by smell or taste. The pure oil is of a light yellow color, with slight odor and taste, and has a faintly acid reaction. It dissolves in thirty or forty parts of alcohol, and more readily in the petroleum oils. It has a specific gravity of about .922. It consists principally of olein, mixed with stearin, palniitin, myristin, cholesterin, and perhaps traces of the butter fats. It seems to contain traces of iodine and bromine, and also certain biliary compounds. It is used largely in medicine, principally in wasting diseases, on account of its easy digestibility. The infe- rior grades are used for soapmaking and for mixing with other oils. It is adulterated with fish oils such as seal or menhaden oil, and also with oil from the livers of other fish. Lard oil and some of tlie seed oils are also often added to it. With sulphuric acid it gives a red spot with more or less violet around it. This is probably due to cholic acid produced from the biliary com- pounds present. TESTS FOR BUTTER. 65 LABORATORY EXPERIMENTS. TESTS ON BUTTER, OLEOMARGARIN, GLYCERIN, AND OILS. I. Butter. — Put inost of the butter into a flask, add about 25 c.e. (one-Iuiir tb_e small llask full) of alcoholic iiotash solution, insert a cork with an upright tube in it, and boil on the water bath for twenty minutes. If the alcohol evaporates nuich during the boiling-, add a little from the shelf. Finall}'^ pour the mixture into an evaporating dish, and dry it thoroughly, at first over the water bath, and, when nearly dry, by heating it very gently and cautiously over the sand bath, stirring constantly with a rod. Add a little of this dry residue (a butter soap) to some water in a test-tube, warm a little and shake = lather. Mix the rest with some water and return it to the flask, filling the flask about one- third full. Add about 10 c.c. of H2SO4 dil., and notice how the fatty acids rise to the top. Fit in the distilling-tube, as under Lesson V., and distil off the "volatile fatty acids" into a small beaker. Test this distillate as follows : 1st. Smell it ; notice the rancid smell of the butyric acid. 2d. Notice its acid reaction to litmus paper. 3d. Add an equal amount of alcohol to the distillate, and then, •with care, a quarter as much common HoSC),. AVhile hot, notice the "pineai)ple" odor of butyric ether (ethyl butyrate). Special Test for Batter and Oleomargarin. — While preparing and caring for the above, make the following tests : Put a little butter in one test-tube, and a little oleomargarin into another. To each add one inch or so of alcoholic potash solution, and warm each in the steam of the water bath. Dis- tinguish the one from the other by the smell. Add a little HoSOi dil. to each and smell again. Notice that the "oleo" test- tube will only smell of alcohol, but that the other will stnell, besides, of butyric ether. 66 MEDICAL CHEMISTRY. II. Glycerin.— C3H6(OH)3. — (a) Notice its taste, stickiness, and solubility in water. (&) Dip a glass rod in it and hold it in the flame ; notice that it burns with a hlue flame. (e) Heat a little in a test-tube with a few drops of common H2SO4 ; notice the acrid, irritating smell of acrolein. III. Castor, Olive, and Cod-Liver Oils. — {a) Try to dissolve each, in separate test-tubes, with gasolene. The last two dissolve read- ily, but, if a good deal of solvent is used, the castor oil does not dissolve, but, combined with some of the gasolene, stays at the bottom of the test-tube. {b) Try to dissolve each, in separate test-tubes, with cold alco- hol. Notice that only the castor oil dissolves with readiness. (c) Put two or three di-ops of each into separate evaporating- dishes, and add, with great care, one drop of eonniion H2SO4. .Notice the peculiar color produced by each oil, as follows: Castor oil, brown in the centre, yellow outside. Olwe oil, brownish in the centre, olive-green outside. Cod-liver oil, reddish-brown in the centre, purple outside. {d) Emulsify olive oil by shaking it in separate test-tubes with water and a few drops of the following reagents : 1st. NaaCOa. 2d. A solution of soap. 3d. NH4OH. 4th. Hydro-di-sodie phosphate, Na2HP04. Look at a drop of one of these emulsions under the microscope, and notice the fat globules. PAET iir. THE PKOTEIDS OR ALBUMI]:^OUS BODIES. THE PROTEIDS OR ALBUMINOUS BODIES. INTRODUCTION. Under this heading Ave include a large and extremely impor- tant class of proximate princijiles, all of which have more or less resemblance to the chief constituent of the white of an egg. Occurrence.— They are found in both the vegetable and animal kingdoms. In the former they occur in greatest abundance in the seeds, although present in smaller quantities all through the plant. In animals, however, they form a large part of the solid constituents of all the tissues and fluids, with the exception onlj' of the sweat, urine, and bile of healthy individuals. Although these substances occur so abundantly in animals, they cannot be formed from other classes of proximate princii)les, excepting by plants. Animals are obliged to absorl) them already formed, and can then assimilate them and modify them as neces- sary. Composition. — All proteids contain carbon, hydrogen, oxy- gen, and nitrogen. Suljihur is present in almost all cases, and phosphorus in a few. Besides this, they almost always leave be- hind, on ignition, a certain amount of ash, chiefly phosphate of lime, which in some cases may be an essential part of the com- pound. As, however, by great care, certain of the proteids have been obtained practically free from any mineral matter, and as the latter seems rather variable in amount, it is probably present in all cases as an impurity. Of the various elements the nitro- gen is by far the most characteristic, so much so that these bodies with the all)uminoids can be spoken of as the nitrogenous con- stituents of the body. This nitrogen does not seem to be obtained by plants directly from the unc(nubinod nitrogen of the air, but from the small quantities of combined nitrogen existing in both air and water iu 70 MEDICAL CHEMISTRY. the form of ammonia and its comi:iounds and the salts of nitrous and nitric acids. . The average composition of tlieproteidsisas follows (Drechsel): C, 50-555?; H, 6.8-7.3^; O, 23.8-24.1^; N, 15.4^18.2^; S, 0.4-5jr. With the exception, however, of this percentage composition, very little is known about the structure of these bodies. They must be composed of molecules of high weight and great com- plexity, and, from the decomposition products, we must assume that in the molecules some of the carbon atoms are arranged as in the aromatic and most of them as in the fatty compounds. General Properties. — The proteids, with some few exceptions, are thoroughly amoriDhous bodies, not crystallizmg, and, except- ing the peptones, and possibly the albumoses and similar decom- position products, not diffusible. They all seem closely related to each other, and perhaps in the living organism can all be trans- formed one into the other. This, however, can only be done in a very few instances in the laboratory. Solubility. — Some of these bodies are soluble and others are in- soluble in water, and of the latter several are dissolved by dilute solutions of neutral salts, sodium and potassium chloi'ide and sulphate, magnesium sulphate, and the like. Most of them dis solve in diluted solutions of acids and alkalies, although, in general, they are changed by this into other proteid compounds. In every ease the solutions polarize to the left. Some dissolve more or less in alcohol, but they are all insoluble in ether. Precipitation. — Several reagents can jDrecipitate proteids from their solutions, especially on the apphcation of heat. Among these are acids, both mineral and organic ; many metallic salts, not only of the heavy metals— mercury, copper, silver, and the like— but also of the alkaline and earthy metals, especially if in excess; and many organic compounds, like chloral, phenol, picric acid, tannic acid, and in some instances alcohol. Of all these, ammonium sulphate in excess is the most efficacious, iJi-ecipitat- ing all proteids but the peptones. Also, in many cases, heat alone, in neutral or faintly acid solutions, will cause proteids to become insoluble. Sometimes Avhen thrown down from their solutions by any of these means, the proteids are precipitated without los- ing their identity, but in many cases, and almost always when THE PROTEIDS. 71 heat has been apphed, they are coagulated— that is chemically altered into insoluble proteid bodies known as coagulated pro- teids. Decomposition.— Thoy decompose readily into simpler products. When heated in the air they blacken, shrivel up, and emit pungent nitrogenous organic compounds, somewhat ammoniacal in structure and properties, with the well-known smell of burnt feathers. They can at last be entirely burnt away, leaving in most cases a trifling amount of ash. By boiling with dilute acids or by the action of certain unorganized ferments, such as pepsin and tryiDsin, they undergo a process of hydration, very similar to the conversion of starch into glucose. By this they are converted into other proteid bodies known as albumoses or the different varieties of peptones, and sometimes into the aromatic non-jiroteid substances— leucin and tyrosin. By organized ferments they are gradually decomjiosed, breaking down, by successive stages, into a large variety of final products, among which are water, carbon dioxide, ammonia, nitric and niti-ous acids, sulphuretted hydrogen, and several more or less simple organic compounds. There are certain simple reactions which, in general, can be said to be common to and characteristic of the proteids. Some of these are given in Lesson VIII., and to the most important of them the name has been given of the General Proteid Reactions. Classification.— It is extremely diflScult, with our present knowl- edge of the composition and i3roperties of these bodies, to lay down any jiermanent scheme of classification. Indeed it seems I^robable that, when we learn enough about them, we shall have to classify them on the basis of their chemical structure, which, as yet, is only dimly hinted at by the nature of the decomposi- tion products, and by the compounds they form with bases. But thus far it is only possible to divide them into a series of groups, the members of which resemble each other more or less in their solul)ility in different media, and their behavior toward certain reagents. Accordingly we shall first separate them into animal and vegetable proteids, and then classify them, as follows : 72 MEDICAL CHEMISTRY. ANIMAL PROTEIDS. Class I. Albumins. — Soluble in pure water; coagulated by heat. 1st. Egg Albumin. 2d. Serum Albumin. Class II. Globulins. — Insoluble in pure water; soluble in di- lute solutions of neutral salts, NaCl, KCl, NasSOi, MgS04, etc. Coagulated by heat. 1st. VitelUn. 2d. Crystalliii (or globulin). (These two are not precipitated in neutral solutions by an excess of salt, and by some authors are considered identical.) 3d. Myosin. 4th. Paraglobu- lin. 5th. Fibrinogen. Class III. Derivei Albumins, — Insoluble in water and neu- tral salt solutions; when freshly precipitated, soluble in dilute acids and alkalies. 1st. Acid Albumins. The name syntonin is generally given to the particular acid albumin formed by the action of dilute hydro- chloric acid on myosin. 2d. Alkali Albumins. Casern is sometimes included under this group of alkali albumins, but differs from them (a) by coagulating at a high temperature, 130 to 150° C, and (b) by being coagulated by rennet in an alkaline medium. Class IV. Fibrin.— Insoluble in water; swollen by salt solu- tions and especially by dilute acids; coagulated on heating in water. Class V. Coagulated Proteids.— Insoluble in water or salt so- lutions and hardly affected by dilute acids; dissolved with some difficulty by hot, strong acids. Class VI. Amyloid Substance or Lardacein. — Insoluble in water, salt solutions, and dilute acids or alkalies; colored brown- ish-red by iodine. Class VII. Albumoses. — Intermediary products between acid albumins and the peptones. All are soluble in dilute NaCl solu- tion, and some in water. They diffuse but slightly if at all, and give a red color with the ])iuret test. Class VIII. Peptones. — Soluble in water, salt solutions, acids, alkalies, and even ammonium sulphate solution. Only precipi- tated by tannin and by mercur-potassic-iodide. Quite diffusible, and give a red color with the biuret test. CLASSIFICATION OF PROTEIDS. 73 VEGETABLE PROTEIDS. Class I. Plant Albumins.— Sohible in water; coagulated by heat. Class II. Plant Globulins.— Only partly .soluble in water: solu- ble in fairly strong NaCl solutions; coagulated by heat. Class III. Plant Caseins. — Insoluble in water and salt solu- tions; insoluble in dilute aleohol. Gluten casein; legumin; congluten. Class IV. Gluten Proteids.— Insoluble in water and absolute alcohol; soluble in dilute alcohol. ALBUMINOIDS. Besi«les the substances included in the above list, there is a large and imjiortant series of bodies, called the albuminoids, which also contain nitrogen, and which are found in both jjlants and animals in close and intimate relations to the proteids proper. They are distinguished from them, however, by not answering to all the general proteid reactions, and by giving different products of decomposition when treated with the digestive ferments, hot dilute acids, and similar reagents. They have not been satisfac- torily isolated from each other, nor is much known about them so far. The most important of them are as follows : Collagen, or gelatin-forming substance. Keratin, or horny suljstance. Spongin, from sponges. Elastin, from the yellow elastic fibres of the connective tissue. Nuelein, froni the nuclei of cells, both animal and vegetable. Mucin, from the secretion of mucous and other glands. These occur principally in the ainmal kingdom, and, in general, in the intercellular sul)stances; whereas the proteids proper occur chiefly in the fluids and in the cells. Thus the organic portion of the bone and teeth, the connective tissue, the main substance of the cartihiges and tendons, the skin, hair, and nails, are all composed of these bodies. They are, with the exception of mucin, insoluble in water; and most of them, on long-continued boiling, are decomposed into substances of the nature of gelatin or glue. Some of them are not digested by the human gastric or pan- creatic juices. LESSON YIII. THE GENERAL PROTEID REACTIONS. THE ALBUMINS AND VITELLIN. THE GENERAL PROTEID REACTIONS. These are certain reactions which are more or less common to all the proteids, and hence are commonly used in testing for their l^resence. 1st. The Xantho-proteic Reaction. — All proteids, whether solid or in solution, are changed, on heating with strong nitric acid, into a yellow substance called xantho-proteic acid. It is a yellow powder insoluble in water, alcohol, or ether, but easily dissolved by nitrip acid, and with bases it forms a series of reddish amor- phous 'salts, which are soluble. These salts are formed with any alkaline solution, such as the hydrates and carbonates of the alkaline metals, or the hydrates of barium and calcium. Care must be taken, however, not to boil over the liquid when adding alkalies to the hot acid solution, and also to get part at least of the mixture thoroughly alkaline before looking for the change in color from yellow to red or to deep orange. The reaction is fairly delicate, and works with not only the proteids but also the albuminoids. 2d. Millon's Reaction. — This is made by heating the proteid with a little of the so-called Millon's reagent, an acid solution of nitrate and nitrite of mercury, formed by dissolving one part of mercury in two parts of strong nitric acid, sp. gr. 1.42, and dilut- ing the solution with twice its bulk of water. The proteid is changed into a dull red precipitate, some of which sometimes dis- solves in the liquid, giving that a reddish tinge. When this test is tried in the presence of much salt, it often fails, owing to the formation of mercuric chloride instead of the nitrate and niti'ite. This reaction does not answer Avith all albuminoid substances, but for proteids it is a characteristic test. It acts as well with THE GENERAL PROTEID REACTIONS. 75 solid proteids as with the solutions, if a little water is added with the reagent before boiling. 3d. The Biuret Reaction.— On adding to a jiroteid solution a little eupric sulphate and then an excess of either caustic or carbonated alkali, the liquid is colored violet or, in the case of the albumoses and peptones, reddish. The color is intensified by boiling, but it is .sufficiently delicate in most cases in the cold, and then has the great advantage of not being obscured by the pres- ence of a reducing carbohydrate. When the proteid solution to be tested is weak, it is best to dilute the copper solution very much, and to add it in very minute quantities. If an excess of copper is admitted, the resultant blue precipitate hides the test. In making this test on a piece of insoluble j^roteid, it is best to soak it for a minute or two in very dilute eupric sulphate, and then to pour that off and to add a dilute solution of sodic and potassic hydrate. The whole lumii generally turns a deep violet- color. This reaction is not quite as delicate as the previous ones. The color is the same as that obtained by the same reagents from biuret, the peculiar crystalline body obtained by heating urea. 4th. The Ferro-cyanide Reaction.— A few drops of potassic ferro-cyanide have the property of precipitating proteids from a solution rendered acid by acetic or hydrochloric acid. If the so- lution contains much sodium chloride or other salts, it is fre- quently necessary to dilute it with water before the proteids will precipitate. The precipitate may form quite slowly if the solu- tion is very weak, but the reaction is still clearly percejitible. 5th. Sodic sulphate Reaction.— A saturated solution of sodic sulphate is also able to precipitate proteids from an acid solution. Acetic acid should be used in preference to hydrochloric, as the latter might dissolve some of the precipitate. The solution of sodic sulphate should be saturated and should be about equal in quantity to the solution of proteids. On boiling the mixture, the albuminous matter is completely precipitated and can be en- tirely removed by filtering. This is an important reaction in that it furnishes a way for removing proteids from a mixture Avithout introducing any objectionable reagents. 76 MEDICAL CHEMISTRY. Picric Acid Test. — This is the most important of the tests given in this lesson. Picric acid, or tri-nitro-phenol, when added in sufficient quantities to turn the solution acid, is able to com- pletely precipitate ordinary proteids from their solutions. It is very slightly soluble, however, in Avater, so that, if the proteid solution is at all alkaline, it is necessary to add quite a quantity of the reagent. The jsresence of albumin does not interfere with subsequently testing, in the same liquid, for glucose, by adding an excess of potassic hydrate and boiling. Hence this same re- a;;ent will permit the testing for albumin and for glucose in the same test-tube — a matter of some importance when testing urines. THE ANIMAL PROTEIDS. Class I.— THE ALBUMINS. General Properties. — These proteids occur already formed in the animal tissues and fluids. They are soluble in water and are not precipitated in the cold by very dilute acids, by sodic chloride, or by magnesic sulphate. On heating their aqueous solu- tions, as well as by the addition of stronger acids, they are coag- ulated ; that is, converted into the class of coagulated proteids. If the solution is very concentrated, it is all transformed into a solid, elastic mass; if more dilute, a flocculent precipitate forms. Very much diluted solutions, or solutions from which almost all salts have been extracted by long-continued dialyzing, do not seem to coagulate on boiling. They are readily converted into the derived albumin class by heating with acids or with alkalies ; they form special salts, albuminates, with many of the metals, Fe, Zu, Cu, Ag, Hg, and others ; and they are readily digested by the gastric and pancreatic ferments. EGG ALBUMIN. Occurrence and Preparation. — This proteid occurs, in the white of birds' eggs, as a concentrated solution, enclosed in a networli of delicate membranes. On cutting these membranes with Ijrokon glass or a scissors, the solution escapes and can be clarified by straining and filtering. Besides, hoAvever, the egg albumin, wliich is present to the extent of 12 or 13^, this liquid EGG ALBUMIN. 77 contains small quantities of other proteids, i^rohably of the globulin class, a little fatty material and soap, some mineral salts very similar to those found in the blood, and traces of glucose. To obtain pure albumin it is necessary to extract the fats with alcohol and ether, and to separate the salts by long-continued dialysis. In spite of all care, however, it is almost impossible to obtain it in a perfectly pure condition. Properties. — When dried at a low temperature it is a light yel- low, ti-ansparent, vitreous body. It dissolves readily in water to a slightly oi^alescent, tasteless, and odorless solution, which has usu- ally a faintly alkaline reaction, and when concentrated is thick and somewhat viseitl. Its solutions rotate to the left to an angle, so far as we can tell, of about — 8G°. On heating a concentrated solu- tion, like the undiluted white of egg, a turbidity sets in at about 59° C, and the mass becomes solid at about 63° C. Some of the proteid present, however, is not coagulated till a temperature of 74' C. or so is reached. These temi:)eratures, which apply only to the albumin obtained from hens' eggs, vary slightly according to the concentration of the solution and the amount of salts present. This coagulation also occurs not only with mineral acids and with alcohol, but also with ether, a test distinguishing it from serum albumin. Composition. — The chemical composition of egg albumin (Hammarsten) is: C, 52.25; O, 23.67; N, 15.25; H, 6.9; and S, 1.93!?. Very little, however, is known about its chemical structure, ex- cepting that the molecule is large and complicated. A formula for it, given by Liebei-ktihn and adopted by many authors, is: C-oHiiaXioSOsa. This formula was obtained by assuming the sul- phur to be present in the form of a single atom, and calculating from that figure for the other elements, and also by studying the dilTerent salts that it forms with some of the heavy metals. The latter, however, seem to v;iry in composition more or less according to the conditions undiM- wliich they are formed, and it is so difTi- cult to get both them and the albumin itself in a state of purity that the analyses cannot be considered as very accm-ate. As a matter of fact it is perfectly evident, from the different coagulat- ing tem])eratures, that in what wc know as egg albumin are con- tained at least two or three dilTerent proteids much resembling 78 MEDICAL CHEMISTRY. each other, and these must be separated and identified before any satisfactory formula is obtained. Among the metallic compounds mentioned, the one with mer- cury is of importance as the best means of counteracting- the poisonous effects of corrosive sublimate, the antidote for Avhich is uncooked white of egg. Uses. — While egg albumin is principally used for food, it must not be forgotten that enormous quantities of it are every year employed in the arts. It is very largely consumed in dyeing and calico printing, in dressing leather, in glazing cards, bookbind- ings, etc., and especially in photography. In medicine it is used to some extent as an antidote, and also in dressing burns. SERUM ALBUMIN. Occurrence. — This proteid is found dissolved in blood serum (in human blood to the extent probably of 4 to 5%), in lymph, chyle, transudations, and, in minute quantities, in milk. It is also, un- der pathological conditions, found in the urine. Preparation. — It can be prepared in a pure state from serum, by first separating the globulins with magnesic sulphate and then precipitating the albumin with sodic sulphate. It is then , washed, dialyzed as thoroughly as possible, and cleansed with alcohol and ether. The serum albumin of commerce is usually only dried blood serum. Properties. — When pure it occurs as light yellow or brownish scales, readily soluble in water to a slightly alkaline, opalescent so- lution, and in most respects very similar to the egg albumin be- fore described. Its solutions rotate to the left, but the amount of rotation varies considerably according to the source of the proteid. Thus, according to the various authors, albumin from human bood rotates from —63.6° to —64.6°; from horses' blood, —60° ; from oxen's blood, —57.3° ; and from dogs' blood, about —44°. This shows either that the serum albumin from each animal is different, or else that it is impossible to separate the true albu- min from the accompanying globulins and other proteids. The temperature of coagulation also varies considerably with the strength of the solutions, the source of the albumin, and the amount of mineral salts accompanying it. Besides, however, the ALBUMINS. GLOBULINS. 79 difference in rotating power and in the temperature of coagula- tion, there are four distinct points of difference between the egg and the serum albumins. 1st. Egg albumin is rapidly coagulated by alcohol; serum al- bumin but slowly. 2d. Egg albumin is coagulated by ether; serum albumin is in- soluble in ether, but is not actually coagulated. 3d. Egg albumin is less soluble than serum albumin in nitric and in hydrochloric acids. 4th. If egg albumin is injected into the circulation, or even if very large quantities of it are taken into the stomach, some of it may be excreted, apparently unchanged, in the urine, even in healthy individuals. This is not the case Avith serum albumin. Uses. — Serum albumin, in the form of dried blood serum, is l^repared in considerable quantities both for dyeing and calico printing, and for the refining of cane sugar. It enters but sUghtly into our supply of food. Class II.-GLOBULINS. These substances differ from the preceding class by being in- sokible in water. They dissolve readily, however, in the presence of small amounts of neutral salts such as XaCl, ]S^a2S04, or MgS04. As it is almost impossible to separate, even by long-continued dialyzing, the last traces of these salts from jiroteid bodies, and as the globulins are coagulated by heat as well as the albumins, it is a matter of great difficulty to distinguish between the two classes. Hence in the case of the white of egg or blood serum, for instance, Ave are still in doubt as to how much of the i:»roteid present is really albumin and how much is globulin. All globulins are precipitated by a great excess of water, and, excepting vitellin and crystallin, by an excess of sodic chloride, or by saturation at 30^ C. with magnesic sulphate. They are gradually altered by standing under water, till they lo.se almost entirely the property of dissolving in salt solutions. Their neu- tral solutions are coagulated by heat. They dissolve without change in very dilute alkalies and are reprecipitated from the solutions by dilute acids. By stronger alkalies, as avcU as by an 80 MEDICAL CHEMISTRY. excess of mineral acids, they are changed into the corresponding derived proteids. VITELLIN. Occurrence. — This is found in the yolk of hens^ eggs to the amount of 14 or 15^. It is associated with small quantities of the other proteids, and with the albuminoid nuclein ; also with the ordinary fats, olein and palmitin, with the peculiar semi- fatty material lecithin, with cholesterin, and with some inorganic salts. Besides these, there is present a peculiar coloring matter known as lutein, which is the same as that contained in the cor- pora lutea, and seems to stand in close relationship to the coloring matters of blood serum, butter, and bile. It seems to owe its color to the presence of small quantities of iron; it is decolorized by sunlight and is turned blue and finally decolorized by strong nitric acid. Preparation.— From this complex mixture we are unable to extract the viteUin absolutely pure. Hence we cannot tell posi- tively whether it is identical with or only very closely allied to the similar proteids found in the yolk of the eggs of other birds, of fishes, of amphibians, and of reptiles. It is also very closely related to those found in chyle, and especially to crystallin, the main constituent of the crystalline lens. It is best prepared by thoroughly extracting from the yolk the fats and yellow coloring mattei's, and then by dissolving the cheesy white residue in 8 or 10.'? salt solution. To purify it, it is precipitated with an excess of water, and then redissolved and reprecipitated as often as is thought desirable. Properties.— Thus obtained it is a white, flaky substance, a con- centrated solution of which, in 10^ XaCl, coagulates partially at 70'^ C. and wholly at 75" C. It is not precipitated by saturation with salt, and dissolves readily in dilute acids and alkalies to the corresponding derived albumins GENERAL PROTEID REACTIONS. 81 LABORATORY EXPERIMENTS. THE GENERAL PROTEID REACTIONS. EGG AND SERUM ALBUMIN, VITELLIN, ETC. I. Preparation of Egg Albumin.— Break out, with the three- cornered file, a small hole in the shell of an egg, and through this hole pour the white, leaving the yolk inside for future experi- ments. Keej) in a test-tuT)e about one inch of the white for ex- periment (/). Put the rest in the bottle, shake it quietly with the Ijroken glass, add about twice its bulk of water, and filter the mixture into a small beaker through a wet piece of muslin. II. General Proteid Reactions. — Make the following tests upon the above solution, as well as on solutions of dried egg and serum albumin : 1st. A'antho-proteie iJ^^ac^/o?*.— Fill a test-tube half full of the solution, add half an inch of HNOs cone, and warm = yellow. Di- vide this solution among three test-tubes. To (a) add an excess of NH4OH, to {b) add excess of NaoCOs, and to (e) add excess of KOH. Notice that in each case the yellow solution turns orange. 2d. Biuret Reaction.— To the solution in a test-tube add a drop of CuSO^ and then half an inch of KOH = violet color. This test is more delicate if the CuSOi is diluted before using, and if very small quantities of it are used. 3d. MiUo)i's Reaction. — To the solution in a test-tube add a few drops of Millon's reagent and boil = reddish curdy ppt. 4th. Feno-ci/anide Reaction. — To the solution in a test-tube add a few drops of acetic acid, HCjHaOa, and then a drop or two of potassic ferro-cyanide, K4FeCyc = white ppt. ."ith. S()dir-.s'iilj)hate Reaction.— To the solution in a test-tube add a little HCsHaO^, and then an equal amount of sodic sul- phate, NajS04. Boil = white ppt. Also, 6th. Take some dry egg and .serum albmnin in the forceps and hold them in the flame; notice the " burnt feather" smell. 82 MEDICAL CHEMISTRY. 7th. Put ill a small test-tube about half an inch of very strong albumin solution, with some undissolved albumin mixed with it. Add about one inch of glacial acetic acid and warm for a few minutes. Cool, add gently about one inch of common H2SO4, let it stand, and notice the fine deep violet color. 8th. Picric-acid Test.— To the solution in a test-tube add a few drops of picric acid = white ppt. Compare the delicacy of this test with that of the tests I^os. 1 to 5, above. To the solution add half an inch of KOH and boil. The ppt. redissolves and the liquid is slightly darkened in color. III. Special Tests on Egg and Serum Albumin. — Make the fol- lowing tests on the same three solutions : («) Add a few drops of alcohol = ppt. Notice that in the serum albumin the j)pt. dissolves in an excess of water unless it has stood too long. (&) Add a little CUSO4 = bluish floeculent ppt. (copper albumin- ate). (c) Add a little AglSTOa = white ppt. (silver albuminate). {d) Add a little HgCla = white ppt. (mercury albuminate). (e) To half an inch of egg-albumin solution in a test-tube add the same amount of ether, and shake vigorously. Let it stand a few minutes; notice that the albumin becomes coagulated. Repeat with serum albumin = no coagula- tion. N.B. — This test is rather troublesome. (/) Fit the thermometer, by means of a perforated cork, into a test-tube containing one inch or so of undiluted Avhite of egS'i fi'om I. Wanii very gently in a large beaker full of water, and notice temperature of turbidity (about 59° C), and of coagulation (about 63° C). IV. Tests on the Yolk of an Egg. — Place the yolk, saved from I., in a small evaporating dish. Break it and test as follows: A. Vitellin.—Vvit about half an inch of yolk into a small test- tube and shake it well Avith three or four times that amount of ether. Let it settle, decant off the ether into a small evaporating dish ; add more ether, shake, and decant again into the same dish. The whitish-yellow residue insoluble in ether, left in the test- tube, is impure vitellin. Let it dry for a few minutes in the steam of the water-bath. Shake a little of it with some water in TESTS ON YOLK OF EGG. 83 a test-tube. Notice that it does not dissolve. Mix all the rest of the vitellin with about three times its Jjulk of lO;^ .salt .solution, and warm gently in the water-bath. Notice that it makes a turbid, whitish solution. Test the solution, filtered if it seems very lumpy, as follows : 1st. Xantho-proteic test. 2d. Biuret test. B. Yolk Oil {Fatty matters, Lutein, etc.). — Warm the ether solu- tion in the evaporating dish, gently and carefully, over a hot water- bath, putting out the flame for fear of accidents. When the ether has evaporated, notice that a yellow oil is left. Put a drop or two of it in water in a test-tube and notice the globules of oil. AVith the rest in the dish mix a drop or two of HNO3 cone, and notice that the yellow color changes to blue and is Anally de- stroyed. Then add a drop or two of water and also of ammonic sulpho-cyauide, NH4CNS; the reddish color shows iron. LESSOR IX. CRTSTALLIN, MYOSIN, ACID AND ALKALI ALBUMIN. CRYSTALLIN (GLOBULIN). It is claimed by many that this proteid is identical with vitellin, described before. It occurs in the crystalline lens associated with, jDrobably, other proteids of the same class, and also with minute quantities of lecithin, cholesterin, fats, and salts. It is prepared by extracting it with a weak solution of common salt, and by preciiDitating and reprecipitating it from this solution by either water or cai-bon dioxide. Its solutions coagulate at from 75° to 85° C. ; they are not precipitated by saturating with NaCl, and are readily changed to acid and alkali albumms. MYOSIN. rormation. — This substance is formed by the coagulation after death of the muscle plasma, a pi-ocess which causes the condition known as rigor mortis. The action is apparently similar to the formation of fibrin in the blood. The living muscular tissue contains a neutral or alkaline, yellowish, opalescent fluid, the muscle plasma. This spontaneously coagulates after death with more or less rapidity owuig, j)erhaps, to the action of a myosin ferment upon a globulin body, myosinogen; and the slender threads and fibres of myosin, as they contract, press out a clear acid fluid, the muscle serum. The change is accomj)anied by heat and by the formation of lactic and other acids and of carbon dioxide. The muscle, after this coagulation has set in, becomes compact and rigid, and is shorter, thicker, and somewhat more dense and more opaque than before. The rigor mortis sets in in man at intervals after death varying from a few minutes to several hours; and it continues for a period varying from one to six or seven days, until relaxed by incipient decomposition. Preparation.— Myosin is obtained by extracting it from muscular MYOSIN. PARAGLOBULIN. 85 tissue with a solution of either salt or ammonium chloride and is purified by precipitation in an excess of water. Properties.— It dissolves readily in solutions containing 10;? NaCl or 14 or 15^ NH.Cl, but is precipitated by an excess of salt. It dissolves in dilute alkalies without change, and with 3 or ifc hy- drochloric or other acids it forms compounds known as acid my- osins. By very weak hydrochloric acid (0.2;;) it is converted into syntonin, from which it can be again produced by the action of lime and NH4C1. It coagulates partially at 40 to 45" C. and in flakes at about .50" C. It is readily attacked by both pepsin and tri^ysia, as is shown by tlie ready digestibility of meat. PARAGLOBULIN. {Serum Globulin.) Occurrence. — This i^roteid occurs in blood serum associated with serum albumin, and probably to about the same extent, i.e., from 3 to 5,'?. It can be separated either by diluting serum some eight or ten times with water and then thoroughly satu- rating it with carbon dioxide, or else by v>arming serum to 35° C. and saturating it with crystals of MgS04. The paraglobulin is then washed and purified l)y successive solution and precipitation. Properties. — Paraglobulin dissolves most readily in NaCl solu- tions of a strength of 5 to lO,'?. In a solution containing less than 0.1;? it is practically insoluble. It dissolves readily in dilute alkalies, from which it can be reprecipitated by CO2 or by dilute acids. When held in solution by salt it coagulates at about 75° C. It sometimes occurs, associated with serum albumin, in path- ological urines, but as the oi'dinary tests for the two proteids are identical and as there is no special significance that we know of in the presence of one rather than the other, we rai'ely take the trouble to distinguish them. The tests on this protoid are given in Lesson XIX. FIBRINOGEN. Occurrence. — This name has been given to a substance occur- ring in the blood plasma, chyle, lymph, hydrocele fluiil, and other coagulable fluids of the body, which, on contact with a little known fibrin ferment, is converted into fibrin, and thereby gives rise to the phenomenon of coagulation. 86 MEDICAL CHEMISTRY. Preparation. — It can be obtained by letting blood run directly from the vessels into a solution of MgS04, then sepai*ating the cor- puscles, and precipitating the fibrinogen bysaturating the solution with NaCl. The precipitate is filtered off and dissolved In 8% NaCl solution, and is cleansed by reprecipitating and redissolving two or three times with saturated and with 8% NaCl solutions. Properties. — The fibrinogen thus obtained dissolves completely in NaCl solution, and is readily precipitated by saturation with either NaCl or MgSOi. If dissolved in a pure salt solution, it is also precipitated by carbon dioxide. It is coagulated, on heating to 55 or 56" C, to a substance not dissimilar to fibrin, and when this is filtered off there is found in the filtrate another globulin, which, however, is not the same as paraglobulin. If fibrinogen is heated for some time at about 38° C, it loses its power of coagu- lating both with heat and with the ferment. It is altered, by standing under water, until it no longer dissolves in salt solution. If all the alkali salts are dialyzed out, it loses almost entirely the power of coagulating to fibrin. Uses. — Fibrinogen is exceedingly important in its relations to the clotting of the blood. The most generally received theory at present is that the fibrin is formed by the action on fibrinogen of a peculiar ferment, the fibrin ferment, which is spontaneously produced in blood, after death. Indeed certain recent observei's claim to have produced a ferment which will coagulate fibrino- gen and which they call protozym, by special treatment not only of white blood cells, but of leucocytes of the chyle, lymph, and other fluids, pus cells, the stroma of red blood cells, etc., etc. The fibrin produced is not equal in amount, it seems, to the fibrinogen present, and a second proteid is formed at the same time, which seems to be a globulin, but does not coagulate on heating. Class III.— DERIVED PROTEIDS. ACID ALBUMINS. Preparation. — This class of proteids is derived fi'om thj albu- mins, globulins, coagulated proteids, and fibrin by treatment with mineral acids, dilute or concentrated, or with some meta.iiio salts like ferric chloride, mercuric nitrate, and others. SYNTONIN. 87 Properties, — They differ more or less in their percentage com- position, tiieir action on polarized light, and their decomposition products. Indeed, it seems probable that for every memljer of the above classes there is at least one acid albumin to corre- spond. They all, liowever, have certain properties in common. They are insoluble in pure water and in neutral solutions, but readily dissolve in dilute acids. In diluted alkaline solutions they dissolve readily and are probably converted into alkali albu- mins. Tliey aper is destroyed. On metals in general, strong sulphuric acid in the cold acts but slightly. When heated, it converts many of them, Cu, Pb, Hg, and others, into the corresponding sulphates, with evolution of SO2 gas. When diluted, it readily attacks many of the metals, Fe, Zn, Mn, and others, setting free hydrogen. The sulphates thus produced are generally soluble, but there are two or three which are sufficiently insoluble in the ordinary media to serve as good tests for the presence of the acid. The best of these is BaS04, formed whenever sulphuric acid or a soluble sulphate is mixed with a soluble salt of Ba. It is a white, heavy i^recipirate, ex- ceedingly insoluble in water, acids, and alkalies, and hence is a most delicate test. The calcic sulphate is nuich more soluble in water and dilute acid, and is less valuable as a test. The plum- bic sulphate is very insoluble, but is more valuable as a test for lead than for sulphuric acid. It exi^lains the reason Avhy sul- phuric acid or soluble sulphates like Epsom or (ilauber's salts are such good antidotes to lead poisoning. (c) PhysioloijiaaL — Sulphuric acid itself has not been found in man, but its salts are present everywhere, though less in quan- tity than the chlorides. It is extremely corrosive to all the tissues of the body, and hence is not unconnnonly used as a poison, generally externally. In this coiniection it is important to re- member that its action on the skin is not quite as instantaneous as that of strong nitric acid, so that if water cannot be obtained immediately it is still possible to wipe off the acid with a dry rag 9 116 MEDICAL CHEMISTRY. or cloth before the corrosion begins. Tlie proper treatment is to wash it off or dilute it as much as possible with water, and then to neutrahze any free acid with the milder alkalies such as bicar- bonate of soda, magnesia, or even soap. Uses. — Sulphuric acid is more widely used than any other pro- duct of chemical industry It is one of the raw materials in tlie Leblanc soda process. It is used in making fertilizers, in the refining of jDetroleum, the manufacture of glucose, the prepara- tion of nitric acid, ether, gun-cotton, nitroglycerin, and a num- ber of other chemical substances, the extraction of indigo and other dye stuffs, the parting of gold and silver, and in numerous other industries. In medicine the acid is used but rarely, to pro- mote digestion, and for other unimportant purposes; several of its salts, however, are of considerable value. CARBONIC ACID.— H2CO3. History. — Carbon dioxide, or carbonic acid gas, was the first gas to be distinguished from common air. It was observed by Van Helmont in the seventeenth century, who called it " gas sylvestre." It was very carefully studied by Black, in the middle of the last century, especially with regard to the change from caustic to mild or carbonated alkalies. Its composition was accurately determined by Lavoisier, some time after the discovery of oxy- gen. Occurrence.— It is found in small quantities always present in the atmosphere, and especially so around volcanoes or over min- eral springs. It invariably occurs where organic matters are being oxidized, whether by combustion, or by consumption in the body, or by the slower processes of decomposition and decay. Combined, it is found in enormous quantities in the form of the carbonates of calcium, magnesium, iron, zinc, sodium, and other metals, both as minerals or dissolved in water. Preparation. — The simplest way to produce this gas is to de- compose one of the carbonates, usually carbonate of lime, with some acid. The reaction is simplj CaCO^ -f H,SO. = CO. + CaS04 + H2O. On a large scale, however, it is often more cheaioly prepared by CARBONIC ACID. 117 igniting limestone, as in Lesson XIV., or by the combustion of coke or charcoal. Properties. — (a) Physical. — Carl)on di(;xide is a colorless gas with a rather sharp taste and an acid smell. Its specific gravity is 1.529 compared to air as 1 ; and hence it can be caught in an open ves- sel bypassing the gas in at the bottom and letting it rise and dis- place the air above. It dissolves I'eadily in both water and alco- hol, one volume of the former at 15' C. absorbing just about one volume of the gas. It supports neither combustion nor life. It can be liquefied without much difficulty, and is sometimes prepared for market in a liquid form. {b) Chemical. — The dry gas possesses no acid properties, but when it dissolves in water a true acid, carbonic acid, is formed, i.7hich colors litnms paper red, and forms salts with metals and bases. With this acid, as well as with sulphuric and other dia- tomic acids, we have two distinct sei'ies of salts, the normal salts where the metallic atoms replace the hydrogen completely, and xhe acid or bi-salts, where half the hydrogen only has been re placed by the metal. The normal carbonates, excepting those of the alkaline metals, are insoluble in water and alkaline liquids, and hence serve as good tests for carbonic acid. The acid salts, on the other hand, are usually soluble, and, as they are formed by the action of COa and water upon the normal carbonates, they furnish a simple way of dissolving the latter. Thus, in the case of lime, CO., + Ca(OH)a = CaCOs + H^O Calcic Hydrate. Calcic Carbonate. CaC03 + H.O + COo =:Ca(HC03)2 C'alcic Bicarbonate. Ca(HC().). heated = CaCOa + H,0 + COo All these carl)()iiatos are readily decomposed by even quite di- lute acids, with lil)eration of carbon dioxide and water. (c) Physiological .—This gas is excreted from the body in large quantities, being produced ))y the oxidation of the carbon in the food. It also is the source of carbonaceous material to green plafits. "When inhaled in large ciuantities it exerts a peculiar ana'sthetic effect, V)ut it can hardly be considered a true poison, deaths from it resulting from suffocation. When present in unusu- 118 MEDICAL CHEMISTRY. ally large amounts in the atmosphere, it is usually associated with a diminution in the quantity of oxygen present, and with the presence of other really deleterious bodies, carbonic oxide, poi- sonous nitrogenous bodies, and the like. When taken into the system in the form of effei'vescing beverages, it acts as a slight stimulant to the appetite and to digestion. Uses. — Besides its functions in nature, this gas is prepared on a large scale and in a very pure form for the manufacture of car- bonated waters. It is sometimes used for extinguishing fires, and the liquefied gas has been prepared for producing artificial cold. It is an important reagent, not only in the laboratory, but also in some quite important chemical industries, such as the man- ufacture of bicarbonate of soda and of potash, and other products. NITRIC ACID.— HNO3. History. — This acid was, under the name of aqua fortis, one of the most valuable reagents known to the alchemists. Cavendish, 1784, determined its composition, producing it from nitrogen and oxygen in the presence of water. Occurrence. — It is found in minute quantities free in the at- mosphere, being produced by electricity. Its salts, especially the nitrates of soda, potash, and lime, are almost universally distrib- uted wherever nitrogenous organic matter has undergone decom- position in the presence of mineral matters. Hence they are found, in small amounts, in all waters and in all soils; and in certain hot countries, where oxidation is rapid and the rainfall very in- termittent, they can be extracted from the surface of the ground in large quantities. Potassic nitrate, or salt^Detre, conies chiefly from India ; while the sodic nitrate, or Chili saltpetre, comes from the deserts of Chili and Peru. Properties. — (a) Physical. — Pure nitric acid is a colorless liquid, fuming in the air, of an acid odor and a very bitter and acid taste. It absorbs moisture quite readily, and when mixed with water it contracts slightly and rises in temperature, but not nearly so much as sulphuric acid. {h) Chemical. — It is a powerful oxidizing agent, giving up its oxygen readily and itself decomposing according to the following reaction : 2HNO3 = 80 + HiO -f 2N0. NITRIC ACID. 12;, The :^0, M-hioh is a colorless gas, takes up oxygen from the air and is converted into the red gas NO2. In this way nitric acid oxidizes most organic substances, not only coloring matters, but tissues and fabrics of all sort. Upon the body it is extremely corrosive, acting instantaneously, and leaving deep yellow or orange stains, owing to the xantho-proteic reaction previously described, upon all proteid or albuminoid material— skin, nails, llesh, wool, or silk— with which it comes in contact. Nitric acid acts readily upon the metals, oxidizing them accord- ing to the above reaction, and then in most cases dissolving the oxides thus formed to nitrates, with the production of water. Thus when copper is dissolved in nitric acid, the following reac- tions take place : aCu + 2HNO3 = 3CuO -f- H2O -f 2NO, and then 3CuO -j- 6HNO3 = ;3Cu(N03). -f 3H»0. The cupric nitrate thus formed, like the cupric sulphate, is con- verted by caustic alkali into cupric hydrate, Cu(0H)2, which dis- solves in an excess of ammonia, in solutions of glucose, and, as in Fehling's solution, of Rochelle salt. Metallic iron is able to replace the copper in this and other acid solutions, deposit- ing metallic copper and itself going into solution. The only tests for this acid depend upon certain color reactions with various mineral and organic substances. With ferrous sul- phate, in the presence of strong sulphuric acid, a peculiar dark brown liquid is produced, a compound of NO Avith two molecules of FeS04. This is an unstable compound and is readily decom- posed by heat. With organic bodies in general, the acid, especially in the pres- ence of concentrated sulphuric acid, forms compounds containing the so-called radical nitryl, NO,. Thus with phenol we form the compounds mono-, di-, and tri-nitrophenol (the latter is picric acid) according to circumstances, all of which bodies have a decidedly yellow or brown color. With anilin the color, Avhich is not in all cases a very striking one, is produced by the formation of mono-, di-, and tri-nitroanilin. The test with brucine is interesting as an example of the color 120 MEDICAL CHEMISTRY. reactions by which tlae various alkaloids are disting-uished from each other. (e) Physiological. — Mtric acid, when concentrated, is almost as corrosive as oil of vitriol, and acts with greater rapidity. It needs the same treatment. Uses. — This acid is largely used in the manufacture of various nitro-compounds — gun-cotton, niti'Ogiycerin, picric acid, and others — used principally for explosives, and also in the prepara- tion of the coal-tar colors. Several of the salts made from it, such as silver and lead nitrate, are important. Either this acid or its salts are essential to the manufacture of sulphuric acid, and the saltpetres form the most expensive constituent of gun- powder. The acid is occasionally employed in medicine as a caustic, and is a most important laboratory reagent, being con- stantly employed for reactions and tests. LABORATORY EXPERIMENTS. SULPHURIC, CARBONIC, AND NITRIC ACID. I. Sulphuric Acid,— H2SO4. 1st. Action on Organic Substances. — Pour some common H2SO4 into a small beaker, and near it place a saucepan almost full of water. Dip a piece of filter paper in the acid, take it out in- stantly, and wash it well in the water. Notice that the filter paper has been converted into parchment paper, having a smooth, gelatinous texture, and greatly increased sti^ength. Notice that a longer exposure destroys the paper. Also notice the rapid charring action of the common acid on paper, cloth, and pieces of wood, especially if they have been moistened first with water. 2d. Action on Water.— Halt fill a small beaker with water, and into it pour slowly and carefully some of the common H2SO4. Notice how great a heat is generated by the mixture. 2d. Tests for IliSOt and for Soluble Sulphates: (a) With Barium. — Put some baric chloride, BaCl^, in a test- tube and add a drop or two of diluted HoSOt = white ppt. of BaSOi. Notice that this ppt. is insoluble in acids TESTS FOR SULPHURIC ACID. 121 or in alkalies. Repeat this test, using magnesic sulphate, MgSOj, instead of the HjS()4, and then notice how clearly the test shows, even with extremely dilute solutions of acid, or of MgSOi, or of the BaCU itself. (6) With Calcium.— Vni some calcic chloride, CaCU, in a test- tube and add a drop or two of diluted H..S04=white ppt. of CaSOd. Repeat this test with more and moi-e diluted acid, and when the limit of the test has been reached notice that the addition of BaClj will still cause a ppt. (c) With Lead.—Vut some Pb(C2H3 02)2 in a test-tube, and to it add a few drops of diluted IIoSOi = white ppt. of Pl)SOi. Notice how much more delicate this test is than the test for CI with Pb salt, as under Section IV. in Lesson XI. II. Carbonic Acid.— HoCOa (CO^ + H.O). Place limestone in a flask, add HCl dil., and pass the gas into water in a beaker, and also into a dry beaker. Smell and taste the water solution, and notice acid reaction of the solution to test paper, and also, if the paper be wet, of the gas. Dry the test papers and notice that the blue color returns. Also, (a) Light a match and i^lunge it into beaker of the gas; it is extinguished. (b) Pass the gas into Ca(OH), = ppt. of CaCO-,, which dissolves in an excess of the gas, and is precipitated from this solu- tion by boiling. Add some NasCOa to the following reagents in different test- tubes: BaCl., MgS04, HgCl., PbCC^H.O.,).., and AgNO.. Notice that in each case a ppt. is produced. Let them stand a little, pour away the top licjuid, and to each add some HNO3. Notice that in each case the ppt. dissolves, with evolution of CO-.. To NaaCOa in different test-tubes add a few drops of each of the following acids: HCl, HNO3, HsSO,, HC.H3O.. Notice that in each case COo is liberated, even if the acid is nuicli diluted. III. Nitric Acid.— HNO3. (a) Preparation.— Vletce the saltpetre, K or NaNOa, in a flask, cover it well with common HjS04, coat the cork of the distilling-tube with paraffin, and carefully distil off the HNO3 into a dry flask or beaker, as in Lesson V. 122 MEDICAL CHEMISTRY. Do not clog the tube with paraffin ; f5t the cork tightly ; wii*e in the cork if it keeps slipping out of the flask ; heat gently, but keep the mixture boihng after the reaction once begins; let the contents of the flask cool before cleansing it, and avoid inhaling the vajDors which pass over with the acid. If the vapors are very dense, hang near the apparatus some filter paper kept moistened with NH.OH. (&) Tests. — 1st. Action on Organic Substances. — Add some of the distilled acid to indigo, fuchsin, and to test papers; notice that it is extremely acid and corrosive, and that in each case it alters and destroys the colors. 2d. Action on Metals. — Put a few drops of strong HNO3 on a copper tack in a test-tube, and warm = reddish brown fumes, NO2, and the metal dissolves. Dilute the solution, Cu(]S'03)2, divide it into three parts, and test as follows : {a) Add KOH = blue ppt. of Cu(0H)2. . (&) Add NH4OH carefully = same blue ppt., which dis- solves in an excess of NH4OH, forming a deep blue solu- tion. (c) Put in that solution an iron nail. Notice that the copper at once deposits on the nail, and that the iron dis- solves, changing the color of the solution from blue to yellow. After a few minutes add NHiOH to the solution = brownish red ppt. of Fe2(0H)6. 3d. Ferrous Sulphate Test.— Vnt in a test-tube half an inch of common HoSOi. Add gently a concentrated solu- tion of FeSOi, cool it, and down the sides of the test-tube run two or three drops of diluted HNOa = brown or black ring. Shaking or heating the liquids will spoil the test. 4th. Phenol Test. — Put in a test-tube one or two drops of phenol and about four times as much conniion H2SO1. Mix till they dissolve, and to the solution add a drop or two of much diluted HNO3 = deep reddish-brown color. 5th. Aniline Test. — Put one or two drops of aniline in a small test-tube, full of H2SO.1 dil. Mix till they dissolve. Place one or two drops of the solution in an evapca-ating- TESTS FOR NITRIC ACID. 123 dish, with several drops of common H2SO4, and stir with a rod dipped in much diluted HNO3. Notice the red streaks, deej^ening to a dark red or brown color. 6th. Brucine Test. — Put in an evaporating-dish a few cry.stals of brucine, and dissolve them in a drop of common HaSOj. Stir with a rod dipped in much diluted HNO3, and notice the deep red color, soon fading to a reddish yellow. Then add a drop of stannous chloride, SnCla, diluted three or four times with water, and the color changes to a reddish violet. LESSOIN- XIIL PHOSPHORIC ACID, IRON, AND ALUMINIUM. (ORTHO-) PHOSPHORIC ACID.— H3PO4. Occurrence. — This acid never occurs free, but its salts are very "widely distributed in natui'e. In the mineral kingdom they occur in many ordinary rocks, and invariably in the soil, while large and valuable deposits of phosphates of lime occur in many local- ities. Traces of phosphates are also found in most natural terres- trial waters. These salts occur in all the juices and hence the tissues of both plants and animals, and in almost all the latter they form by far the greater amount of the mineral matter of the skeleton. Preparation. — The pure acid can be prepared by oxidizing phosphorus with nitric acid ; on a large scale, however, it is usu- ally obtamed from bone ashes by treatment with acids, separa- tion as calcium, lead, or barium phosphate, and decomposition of the latter by sulphuric acid. Properties. —Phosphoric acid, when perfectly pure, can be ob- tained in the form of white crystals, very soluble in water. It is usually met with in the form of an aqueous solution, with no odor and, when not too strong, a pleasant acid taste. It forms with metals three series of salts, according to whether one, two, or three atoms of H are replaced. Thus, with sodium we have the normal sodic phosphate, NasPOj, which is decidedly alkaline; the hydro-disodic phosphate, which is slightly alkaline; and the dihydro-sodic phosphate, or acid phosphate of soda, which has a decidedly acid reaction. Tests.— The most delicate test for phosphoric acid and the solu- ble phosphates is the formation of a yellow crystalline compound with a nitric acid solution of animoniuin molybdate. This pre- cipitate, called commonly ammonio-phospho-molybdate, aijpears PHOSPHORIC ACID— IRON. 125 with the least traces of phosphoric acid, and, while readily dis- solved in alkalies, is very insolulile in acids, especially nitric acid. It contains only about Wjc of phosphorus. The ammonium magnesium phosphate, commonly, though er- roneously, called " triple phosphate," is of more importance as a test for magnesium, and on account of its presence in urine, than as a test for this acid. It is discussed in the next lesson. The argentic phosphate is of importance as distinguishing a solution of the ortho-salt or acid from solutions containing the meta- or pyro-phosphoric acid. Tlie latter also form precipitates with argentic nitrate, but they are white. IRON.— Fe. Atomic weight, 56. Occurrence.- This element is occasionally found in a free state either in the form of meteorites, or in igneous rocks as a product of reduction. In combination it is present in large or small quantities in all the ordinary rocks, in the soil, and even in all terrestrial waters. It is found in both animals and plants, and is an essential and probably the active ingredient of both chloro- phyll and hjemoglobin. Preparation.— Iron is extracted from its ores, which are either oxides or carbonates, by reduction with coal. The cast iron thus produced contains considerable carbon, besides silicon, and usually traces of sulphur, phosphorus, and manganese. It is converted into wrought iron, which is a very pure form of the metal, by a process of oxidation, and this is converted into steel by combining it with the proper percentage of carbon. Properties.— (o) P/jj/.s/co/.- Wrought iron is a rather soft, malle- able, infusible metal of a specific gravity of 7.8. It differs from almost all other metals by having the property of welding, and also of becoming magnetic. (6) Chemical.— 'The various compounds of iron may be divided into two distinct classes, which, excepting for the fact that the one can be converted into the other, are as separate as if they belonged to two different elements. In the ferrous compounds one atom of iron is present, and is considered to have two •' bonds," 126 MEDICAL CHEMISTRY. i.e., to be able to unite with two monatomie atoms or radicals like chlorine or hydroxyl, OH, or with one diatomic atom or radical, like oxygen or the SO4 group. Thus, ferrous chloride is FeCU ; ferrous hydrate re(0H)2 ; ferrous nitrate Fe(N03)2, etc. : while ferrous oxide is FeO, ferrous sulphate FeSO^, and ferrous car- bonate FeCOa. The ferric compounds, on the other hand, contain two atoms each of u"on, combined together with one bond, and with three bonds from each atom, or six bonds for the two, to unite with other elements. Hence the graphic formula for ferric chloride, /CI Fe-Cl p /O \C1 \ FeaCle, would be | yr^^■, and for ferric oxide, Fe203, | /0;and Fe— CI ^ ^XO \C1 the formula for ferric hydrate is Fe2(OH)6, and for ferric sulphate is Fe2(S04)3. These compounds can be converted one into the other by the processes of either oxidation or reduction. Thus the precipitates of the ferrous salts will absorb oxygen even from the air, and be converted into ferric compounds — thus, 2Fe(OH)2 + O + H2O = Fe2(OH)6. Ferrous Hydrate. Ferric Hydrate. While the latter, if treated with hydrogen or SO2 or some other 130werful reducing agent, will lose oxygen and be converted into the corresponding ferrous salt. Where nitric acid is used for oxi- dizing, the oxygen is derived from it instead of from the atmo- sphere, and water and NO are liberated, as in the last lesson. Tests. — Among the more important tests for both series of these iron compounds are those made by the ferro- and ferricyanides 01 potash. The latter may be considered as salts of feiTo- and ferri- cyanic acids, HiFeCyo and H6Fc2Cyi2, where the acid radicals are composed of a compound of iron, ferrous and feiTic, with molecules of cyanogen or CN. The ferrous salt of ferrlcyanic acid, or Fe.TFe2Cyi2, is a well-known blue pigment, almost as im- Ijortant as the Prussian blue, the ferrocyanide of ferric iron, Fei(FeCyo)3. By means of these two tests it is easy to distin- guish the presence of one or both varieties of iron in a solution. TESTS FOR IRON — ALUMINIUM. 127 The solution, however, must be slightly acid, for alkalies de- stroy the colors, and strong acids alter the reagents. The tannate of iron, made by adding tannic acid to a neutral solution of ferric iron, has been known for many centuries as a test for iron, and until recently was the source of almost all the ink of commerce. The best test for ferric iron is the formation of ferric ^ulpho- cj-anide by the addition of ammonic or other soluble sulpho- cyanide to a neutral or slightly acid ferric solution. Xo precipi- tate is fonnod, but the compound, when dissolved in water, gives a very characteristic blood-red color, which shows even in very dilute solutions. This color is destroyed by reducing agents or by alkalies, but is restored by oxidation and by acids. ALUMINIUM.— Al. Atomic ive/(/hf, 27. Eistory,— Salts of this metal, especially the alums, have been known since the Middle Ages, if not earlier. The metal itself was first isolated by Oersted in 1824, and AVOhler in 1827, and has been prepared on a commercial scale since about 1850. Occurrence. — It is the most widely distributed metal ia the earth's crust, never occurring free, but generally associated with other metals and combined with silica to form the great mass of common rocks. From their decomposition come the many vari- eties of clay, all more or less pure silicate of alumina. It is not absorbed, however, to any great extent by most plants, nor does it enter into the composition of animals. Preparation. — The metal is now being extracted from its salts by electricity, but it has usually been obtained by heating them with metallic sodium. The sodium combines with the chlorine or other constituent of the salt, and liberates the aluminium. Improvements are being constantly made in the process, and great efforts are being made to cheapen the metal so as to bring it into general use. - Properties.— (ro Physical. —Ahinuumm has many very valuable proi)ertios. It has a bright white color, and its surface polishes well and does not readily tai'uish. It is very strong, and can be 128 MEDICAL CHEMISTRY. easily worked by hammering, drawing, and to some extent by casting. It is very light (specific gravity, 2.6), and is a good con- diictor of heat and electricity. (&) Chemical. — Aluminium is not attacked by nitric acid, but dissolves i*eadily in hydrochloric and sulphuric acids, forming salts similar to those of ferric iron. When heated with potassic or sodic hydrates, it dissolves with evolution of hydrogen and the formation of salts, aluminates, of the metals. Thus : Al, + 2KOH + 2H20 = KoAl204 + 3H2, I. Potassic Ainminate. This same compound is formed when alumuiic hydrate, A12(0H)g, is heated with caustic potash. Thus : Al2(OH)6 + 2K0H = K,A1.204 + 4H2O. II. These aluminates ^re decomposed by an excess of ammonic chloride, and the Al is precipitated as aluminic hydrate. Thus: K2AI2O4 + 2NH4CI + 4H2O = Al2(OH)6 + 2KC1 + 2NH4OH. III. Alums. — Some important compounds, many of which contain this metal, are grouped together under the name of alums. These substances all have a striking resemblance to each other in crys- talline form and in general composition, and in short in most of their physical and chemical properties. The common or potash alum has the composition K2Alo(SOi)4 + 24H2O, and is therefore a hydrated double sulphate of potassium and aluminium. The other alums differ from this in that other metals ai-e substituted for the potassium and aluminium. Thus, instead of i^otassium Ave may have any of the alkaline metals, Na, NH4, or Li; and for aluminium may be substituted iron or chromium, making the iron and chrome alums of commerce. Hence we have a whole series of different alums, such as — Soda alum, Na2Al2(S()4), + 24H20. Chrome alum, K2Cr2(SO.,)4 + 24HoO. Ammonia iron alum, (NH4)2Fe2(SO.,)4 + 24H2O. On heating an aluminium alum before the blowpipe or otherwise, it melts at quite a low temperature (potash alum at 92" C), and on fiirtlier heating the water of crystallization grad- ually boils away, leaving a white porous mass known as burnt COMPOUNDS OF ALUMINIUM. l'^9 alum. This mass, when strongly heated with the addition of a small amount of cobaltic nitrate, forms a compound of aluminium and cobalt known as Th^'nard's blue. This is prepared on a large scale and used as a paint. Tests,— The test for this metal most generally employed is the precipitation of its hydrate by means of an alkaline hydrate. Thus : K.Al2(S04)4 + GNH^OH = Al,(OII)o + 3(NH4)oS04 + K,S04 IV. This precipitate is almost colorless, and, in case any ferric salts were present, would be entirely obscured by the accompanying brown ferric hydrate. The aluminic hydrate differs, however, from ferric hydrate, in that it dissolves, as we have seen in Equa- tion II., on heating with KOH, and, as in Equation III., is re- precipitated by NHjCl. Hence, when it is desu-ed to separate iron from aluminium in any solution, it is only necessary to add an excess of KOH and boil, when the Fe will precipitate as reo(0H)6 and can be filtered out, while the Al remaining in the filtrate can afterward be precipitated by NH4CI. Lakes.— An important property of the Al salts is that of forming colored insoluble compounds called lakes, with most of the dye stuffs. This is very valuable in dyeing and calico printing, for it renders it possible to fasten the colors upon the cloth. The fabric can be first printed with or steeped in a solution of alum, and dried. Then, on passing it into an alkaline bath of the color, the lake will be precipitated wherever the alum was spread, forming a close flocculent compound which on drying adheres firmly around tlie individual fibres. Uses. — The metal aluminium is used more and more every year, as its cost is diminished, for purposes where its lightness, strength, and good color are Avorth the extra expense. The salts, especially the alums, are largely used in dyeing, in tanning leathers, and in some other industries. 130 MEDICAL CHEMISTRY. LABORATORY EXPERIMEIs^TS. PHOSPHORIC ACID, IRON (FERROUS AND FERRIC), AND ALUMINIUM. I. Phosphoric Acid. — H3PO4. — Test some solution of hydro-di- sodic phosphate, Na2HP04, as follows: 1st. Fill a test-tube nearly full of ammonic molybdate (NH4)2Mo04, add a drop or two of HNO3, and then a few drops of the solution = yellow crystalline ppt. Notice under the mi- croscope the star-shaped crystals. 2d. To the solution in a test-tube add NH4OH till it smells of ammonia, and then a little MgS04 = white crystalline ppt., MgNH4P04. Notice under the microscope the white, feathery crystals. 3d. To the solution in a test-tube add a few drops of AgNOs = yellow ppt., Ag3P04. This ppt. dissolves in HNO3 as well as in NH4OH. II. Ferrous Iron. — FeO — Make a weak solution of FeS04 and test as follows : 1st. Add potassic ferrocyanide, KaFeCye = light blue ppt. 2d. Add potassic ferricyanide, KoFezCyia = deep blue ppt. Notice that both these ppts. are decomposed by alkalies. 3d. Add KOH = greenish ppt., Fe(0H)2, turning brown slowly in the air. 4th. Add (NH4)2C03 = greenish-white ppt., quickly turning green. III. Ferric Iron. — FcoOs— To a solution of FeS04 add a few drops of H2SO4 dil., and boil. To the hot liquid add a few drops HNO3 cone, and heat again. Repeat this until the liquid has a yellow or brown color. Then test this solution and also some diluted FeaClo, as follows : 1st. Add KiFeCyo = deep blue ppt., Prussian blue. 2d. Add KoFe2Cyi2 = dark green solution. To this add a few drops of SnCls = deep blue ppt. FERRIC IRON — ALUMINIUM. 131 Notice that both these ppts. are decomposed by alkaUes. 3d. Add KOH = reddish brown ppt., Feo(0H)6. 4th. Add (NH4)2C03 = reddish brown ppt., with evolution of CO.. 5th. Add a solution of tannin in water = bluish black ppt. (ink). Notice that this dissolves in acid ; hence, if solution is very acid, must nearly neutralize with NH4OH before adding the tannin. Cth. Add ammonic sulphocyanide, NHiCNS = deep red color, which is destroyed by alkalies. Compare the delicacy of Tests 1st, 5th, and 0th by tests on very dilute solutions. Dissolve some iron nails in HCl cone, nearly neutralize with NHiOH, and test for ferrous and ferric salts with KiFeCye and with KcFeaCyia. Also test for ferric salts with tannin and with NH^CXS. IV. Aluminium. — Al. — (a) Place piece of Al foil in a test-tube with one inch of KOH, and warm. The Al dissolves with escape of H. gas. To solution add ammonic chloride, NH4CI in excess = ppt. of Al2(OH)6. (6) Place a little dry alum on charcoal and heat in a blowpipe flame ; it boils and becomes burnt alum. To this add a drop of cobaltic nitrate, Co(N03)2, and heat again = a blue mass. (c) Make concentrated solutions both of alurainic sulphate, Als(S04)3, and of potassie sulphate, KaS04, by treating them in separate test tubes with a little hot water. Mix together in a test tube equal quantities of these two solutions, and notice the resulting precipitate of potash alum, K2Ala(S04)4 + 24H2O. Examine this ppt. under the microscope. Dissolve the dry alum in a little hot water, put a drop of the solution on a slide, let it stand quietly for several minutes till it has partly dried, and then examine, under the low power of the microscope, the crystals of alum. Dilute the rest of the solution and test as follows: 1st. Add NH4OH = ppt. of Alo(0H)6, insoluble in excess of NH4OH. , 2d. Add KOH = same ppt., which dissolves in excess of KOH. To this solution add NH^Cl in excess = ppt. of Al2(OH)o. i5d. Mix a few drops of Fe-iCla with the alum solution, and sep- 10 133 MEDICAL CHEMISTRY. arate the Fe and Al as follows. To mixed solution add KOH in excess and boil = i^pt. of Fe2(OH)6. Filter, and to filtrate add excess of NH4CI = ppt. of Al2(OH)6. 4th. Mix with the alum solution some solution of cochineal, add NH4OH, and boil. Notice the red ppt. (crimson lake). 5th. Mix with the alum solution some extract of litmus, add NHiOH, and boil. Notice the blue ppt. (lake). Filter off these ppts. and notice the lack of color in the filtrates. Plate l'"ir.. 5. Calrium Sulpliatc, x IfiO. Fio. C. Caloiuin Carbonate, x 200. c. K. p., deL LESSOX XIV. CALCIUM AND MAGNESIUM. CALCIUM.— Ca. Atomic weighty 40. History.— The metal was first prepared by Davy in 1808. Its eonipounds, however, had been known and used for mortar and cements since the earliest ages. Occurrence. — This metal is never found free, but in com- bination is, next to aluminium, the most abundant metal in the earth's crust. It occurs as carbonate under the forms of lime- stone, marble, chalk, all of which are originally formed from the shells of marine animals and coral. It is found as a silicate asso- ciated with Al, Fe, Mg, and other metals in the common rocks and in the soil, and the sulphate, fluoride, phosphate, and other compounds ai'e among the well-known minerals. As sulphate or bicarbonate it occurs in all terrestrial waters, and as phosphate and to some extent as carbonate it is present in the juices and tissues of both plants and animals and especially in bones of vertebrates. Preparation.— The metal calcium can be prepared from its salts by electricity or by reduction with metallic sodium. Its salts are all derived from limestone either by the action of heat or of acids. Properties. — (a) Physical. — The metal calcium is not important, being expensive to prepare, and oxidizing readily in moist air. It has a yellow color, is tenacious and malleable, is a little harder than lead, and has a specific gravity of only 1.6. It burns in the air when heated to redness, and it decomposes water, with evolu- tion of hydrogen. (6) C/iemical. — Of its different compounds the carbonate is the most important. This compound, when heated to a dull red 134 MEDICAL CHEMISTKY. heat, gives off CO2 and changes to Hme, CaO, according to the simple formula, CaCOs heated = CaO + CO.. This is done on a large scale in lime kilns, and the resulting product is the quicklime of commerce. The latter occurs in white, earthy looking lumps, which must be kept from the at- mosphere or they will "air-slake," «.e., absorb CO2 from the at- mosphere and re-form the original CaCOs. "When water is added to them they slake, i.e., become converted, with change of form and evolution of heat, into slaked lime, or calcic hydrate, Ca (0H)2. This is a white i^owder, slightly soluble in water, forming a weak alkaline solution known as lime water. Mortar is made by mix- ing fresh slaked lime with sharp clean sand, and when it sets it absorbs CO2 from the atmosphere and changes back to calcium carbonate, setting free water. Thus, Ca(0H)2 + CO.2 = CaC03 + H^O. The same reaction takes place when limewater is used as a test for carbon dioxide. Calcium carbonate, precipitated from calcium solutions by CO2 or by soluble carbonates, is a white crystalline substance, insolu- ble in water and alkaline solutions, but readily dissolved by acid, even if much diluted. It also dissolves, as before mentioned, in CO2 and HoO, forming the soluble bicarbonate CaH2(C03')2. Tests. — The formation of calcium sulphate, by the addition of sulphuric acid or a soluble sulphate, is not a very delicate test for lime, for it dissolves to a slight extent in water as well as in acid solutions. It can, however, be prepared without ti'ouble in all concentrated solutions, and it forms characteristic well- defined, white, needle-shaped, radiating crystals. The best test, however, for lime salts, and the one most com- monly used, istlie formation of oxalate of lime by the addition of solutions of oxalic acid or of alkaline oxalates. Magnesium salts are not precipitated with these reagents, so this presents an easy method for separating the two metals. The calcic oxalate thus formed is a white powder, insolul)le in neutral and alkaline solu- tions, and also in weak acids, though dissolving readily in strong MAGNESIUM. 135 acids. AVhen precipitated quickly from concentrated solutions, it has no characteristic shape ; but when allowed to form very slowly from dilute solutions, it sometimes appears in granular or dumb- bell forms; but moi'e usually, mixed with irregular little plates and crystals, it crystallizes in some of the characteristic octa- hedra which we meet with in urine. MAGNESIUM.— Mg. Atomic weight, 24.3. History.— The salts of magnesium were recognized at an early date, but the metal Avas not isolated vintil 1808, by Davy. Occurrence. — Magnesium always occurs in coml>ination. It is found in the mineral kingdom, usually associated with calcium and other metals, as carljonate, phosphate, chloride, and espe- cially as silicate. It occurs in most waters, especially sea and mineral waters, as chloride, bicarbonate, and sulphate, and it is found in both plants and animals, usually as a phosphate. Preparation. — The metal is jjrepared in considerable quantities either by electrolysis or by the reduction of the chloride with metallic sodium. Properties. — (a) P7one black, rinse it once with water, and then filter through it again and again, a little very dilute solution of indigo. Keep some of this same indigo solution for comparison, and notice how the bone black gradually decolorizes it. III. Bone Ashes. — Heat sevei'al small f)ieces of bone, one after the other, on charcoal, with the blow-pipe. Notice that at first they turn black, and give off fumes, but that after longer ignition they turn white again. Now drop them into a little HNOa dil. in a small beaker; warm, and te.st the solution as follows: 1st. Carbonates. — Notice the effervescence of COa from each piece when it enters the acid. 170 MEDICAL CHEMISTRY. 2d. Phosphates.— Fill a test-tube two-thirds full of (lS[H4)2Mo04, and add a few drops of the solution = yellow crystalline ppt. 3d. Chlorides. — Test for these by adding a drop of AgNOs to a good deal of the solution in a test-tube. Notice that, if present at all, they are present in very minute quantities. 4th. Calcium and Magnesium Phosphates. — Put some of the solution in a test-tube and add NH4OH = white ppt. of the so- called " earthy phosphates." 5th. Separation of Ca and Mg in the Presence of Phosphates. — To all the remaining solution, in the small beakei*, add slowly some FcqCIo. After every few drops test the mixture by adding a drop of it to some NH4OH in a test-tube. When the ppt. thus foi-med is yellou\ and not lohite, stop adding FeaClo, and add NaQCOa until the ppt., formed as the latter enters the mixture, is only just redissolved when stirred up with the rest of the liquid, i.e., until the mixture is nearly neutral. Then add half an inch of BaCOs, warm, and filter off the Ba and Fe(ie) phosphates. To the filti'ate add a quarter of an inch of (^£[4)2804, boil, and filter off the BaS04 through a double filter. To this filtrate add a little NH4OH and then (NH4)2C,04 = ppt. of CaC^Oi. Filter, and test for Mg in the filtrate with Na2HP04. Repeat these tests with ashes from the cremating-furnace, dis- solving them in a small beaker with hot HNO3 dil., filtering, and testing the filtrate as above. Notice that these ashes contain more chlorides than the bone ashes, and also give a reaction for u-on with NH4CNS. IV. Ossein (Collagen). — While making these last tests boil the piece of " macerated " bone, for half an hour or more, with a little water in the saucepan. Notice that the bone disintegrates and even dissolves. Test the solution as follows: 1st. By the xantho-proteic, biuret, and Millon's reactions. 2d. Notice that it forms ppts. with {a) picric acid, (6) HgCla, (c) a solution of tannic acid. V. Gelatin.— Place the glue in a little warm water in a small evaporating-dish. Warm very gently over a water bath and notice that the glue gradually dissolves. Put some of this solu- tion in a test-tube and let it cool. Notice that, if sufficiently concentrated, it will gelatinize. Put some of the same solution GELATIN. 171 in another test-tube and boil it Iiard for a few minutes. Notice that, even if concentrated, it will no longer gelatinize. Make the same tests on this solution as on the solution of collagen, above; also — 1st. Add some to a a little alcohol in a test-tube = ppt. 2d. Notice that it is not [jpted by either alkalies or nuneral acids. 3d. Notice that it is not ppted by acetic acid and potassic ferrocyanide. LESSON XV'nL MILK This may be described as a secretion from the breasts of female mammaha Avhich begins a few days after parturition, and is in- tended to serve as sole nourishment for the infant offspring. The secretion, which begins at the end of pregnancy and continues until it is replaced by milk, is known as colostrum. It differs very materially from milk in that it contains from 35 to B0% of Fig. 5.~CoLOf5TRUM, from a Healthy Lying-in Woman, Twelve Hours After DunvERY (Funke). solid matter, mostly belonging to the proteid group, and is full of little cells, known as colostrum corpuscles, which more or less resemble in appearance the white blood cells. Properties. — Milk is a white or light yellow, opaque liquid, with a specific gravity varying, under different conditions, from 1.018 to 1.045. It has a reaction not far from neutral, and indeed is usually amphoteric, i.e., alters the color of both red and blue test paper. It is claimed that this is due to the simultaneous pres- ence of Ijoth alkaline and acid sodium phosphates. Composition. — Milk may be considered as a perfect food. In cow's MILK. 173 other words, it contains representatives of all the classes of proxi- mate principles already discussed, in the proportions best suited to support life. It is an aqueous solution in which are svispended fat globules, casein, and, for some little time after birth, a few colostrum corpuscles. We find dissolved in it milk-sugar, three if not four different proteids, various mineral salts, traces of lactic and acetic acids, of alcohol, lecithin, cholesterin, urea, and cre- atin and also the gases oxygen, carbon dioxide, and nitrogen. Fig. 6. -Human Milk globut.es, from a Healthy Lying-in Woman, Eight Days After Dkhvery (Fl-nke). Its composition varies very considerably, not only with the species of animal, but with the breed and also Avith the indivi- dual. Besides this, from the same individual the milk vai'ies in quality according to the state of health, mental as well as physi- cal, the food, exercise, time of day, length of time since previous milking ;nul since pai'turition, and many other conditions. Cow's Milk. — This milk is so universallj' used that its compo- sition is a matter of considerable interest. The following figures, giveri by K^hiig,* represent analyses made upon several hundred diflferent samples. Water. Casein. Albumin. Fat. Sugar. Salts. Minimum, S0.?,2 1.70 0.25 1.67 2.11 0.35 Maximum, 90.00 4.2:] 1.44 6.47 6.03 1.21 Average, 87.17 3.02 0.53 3.69 4.88 0.71 Human Milk.— Breast milk differs from cow's milk in two or • J. KOuig, " Zusammensetzung der Menschl. Nahr. u. Genussmittel," Berlin, 1889, p. 895. 174 MEDICAL CHEMISTEY. three particulars. It contains considerably more lactose, and less casein. The casein, too, is different from that of cow's milk ; it coagulates less readily and in lighter flocks, and is decidedly more digestible. It is probably on account of this constituent that, in spite of all precautions, it is sometimes almost impossi- ble to make a delicate nursling thrive upon covv's milk. The amount of fat is about the same. Hence it is advisable, when cow's milk must be given to infants, to dilute it with water, so as to reduce the amount of casein, and then to add both sugar (milk-sugar if possible) and a little cream. The following figures are taken from, a series of analyses made with great care and according to modern methods, by Professor Leeds,* upon eighty samples of milk from normal women, whose histories were taken at the same time : Specific Water. Proteids. Fat. Sugar. Ash. Gravity. Minimum, 83.21 0.85 2.11 5.40 0.13 1.026 Maximum, 90.08 4.8G 6.89 7.92 0.37 1.035 Average, 86.732 1.995 4.131 6.936- 0.201 1.0313 Accordingly, in round numbers, we may say that normal breast milk has an average specific gravity of 1.031, and contains about 2;.' of casein and other proteids, 4^ of fat, 1% of sugar, and Q.2% of ash. Another difference between cow's and breast milk, which is especially important with respect to the feeding of young chil- dren, depends upon the fact that the breast milk is fresh and sterile wdien taken, while the cow's milk always contains micro- organisms, and is frequently used when in a state of incipient decomposition. Milk is an excellent culture medium for almost all kinds of microbes, which increase in it with great rajjidity unless the temperature is kept very low. Two Austrian authori- ties, Escherich and Cnopf, have stated that they have found, by the already described plate-cultui-e method, over a million bac- teria and other germs to the cubic centimetre of milk as it is ordinarily handled in summer. Other observers report the finding of five or six hundred times as many microbes in milk that has stood at the ordinary tempei-ature of a room for twenty-four * Jour. Amer. Chem. Soc, vol. vi., pp. 252-280. PROTEIDS IN MILK— CASEIN. 1T5 hours. These germs belong ahnost invariably to the ordinary pu- trefactive, and hence harmless, varieties. But still, Avhen present in such enormous quantities, they, or at any rate their products, must have some deleterious action upon the digestive systems of delicate children. For this reason, wherever milk cannot be obtained perfectly fresh, it is now considered a necessary precau- tion to thoroughly sterilize it before feeding it to infants. Proteids in Milk.— Of the different albuminous substances the casein, Avhich has already been mentioned, is by far the most important. Besides this, there is a little albumin, either the same as or very similar to serum albumin, and also minute quantities of a globulin much like the paraglobulin of the blood. It is also claimed that still another i^roteid, quite similar to the albumoses and called lacto-protein, is present in small quantities. This, however, may be a decomposition product derived from the others. Casein. — The casein is not dissolved in the milk, but is held suspended in it in a thin, loose, swollen condition. It can, in fact, be filtered out by straining milk through clay filters. The casein of cow's milk can be prepared pure, by precipitation from diluted milk Avith very weak acetic acid, and then by frequent solution and reprecipitation Avith dilute alkali and acid. When pure, it is a fine Avliite powder, leaving practically no ash on l)urning. It is insoluble in water, although it I'eddens moist blue litmus paper. It dis.solves readily in alkalies, and the solutions do not coagulate on boiling, but form a scum on the surface. The .scum, liowever, noticed in boiled milk may per- haps be due to the coagulation of some of the all)umin. Casein can be precipitated from its .sohition ])y an excess of salt or by dilute acids, hut it dissolves quite readily in stronger acids, especially in liydrocliloric. Casein is readily coagulated by acids and by the peculiar un- organized ferment known as rennet, or, from the German, "lab." In every case the coagulation seems to depend upon the presence of phosi)hate of lime, although exactly how is not known. Ren- net is present in the stomachs of all iulant maimiialia. and is extracted on a large scale for use in the manufacture of cheese. One part of moderately i)ure ferment is able to coagulate several 176 MEDICAL CHEMISTRY. hundred thousand parts of casein. When casein is coagulated by the ferment, it seems to produce, at the same time, small quantities of a soluble pi'oteid which remains in the whey and i. known as whey albumin. Milk-Sugar.— This carbohydrate has already been discussed under Lesson IV. Its principal point of difference from the other sugars and from the glucoses is the fact of its fermenting to lactic acid. This occurs spontaneously when unsterilized milk is allowed to stand at an ordinary temperature. The acid thus produced is strong enough to cause coagulation of the casein. The reaction is supposed to be one of hydration, as follows : Ci2H220ai + H2O = 4H.C3H5O3 Lactose Lactic Acid. It is always accompanied, however, in the case of milk, by a slight evolution of CO2, and by the production of small quanti- ties of other compounds, probably owing to the i^resence of other ferments. The true lactic fermentation is due to different varieties of bacteria, some of which, as, for instance, Bacillus acidi laetis, have been carefully studied. It takes place most rapidly at a temperature of 30 to 40° C. and entirely ceases when the milk is cooled to 2 or 3° C. It is of course hindered by the various anti- septics. Milk is such an excellent culture medium, however, for mi- crobes of all sorts that it not infrequently undergoes other fer- mentations as, for instance, turning blue under the action of Bacillus cyanogenus, turning slimy, or cheesy, or bitter, or, more important than any of these, developing the poisonous ptomaine tyrotoxicon. This latter, the active agent in the poisonous milk, cheese, and ice cream, of which so many cases are constantly occurring, is undoubtedly caused by the growth of some microbe not yet identified. Its symptoms resemble very closely those produced by poisonous mushrooms. They are constantly being mistaken for the symptoms of an acute metallic poison, such as copper or arsenic, but are much less permanent in their effects. Inorganic Constituents. — Tlie mineral salts of milk are but small in quantity. The most important of them is the phosphate of calcium. Besides this we find present the phosphates and BUTTER FAT— ADULTERATION OF MILK. 177 chlorides of potassium and sodium, with small quantities of sul- phates, and also of magnesium salts. There is the merest trace of iron, probably contained in the yellow coloring matter of the fat. Butter Fat.— This has already been described under Lesson YII. It occurs in milk in the form of small globules, varying in size from 0.0015 to 0.01 mm. Besides the fat, these globules con- tain small quantities of cholesterin and lecithin, and also a little yellow coloring matter which seems very similar to the lutein from the yolk of an egg. It has often been suggested that each globule is enclosed in a little bag of proteid mattter which must be burst in the process of churning, before the butter can collect in lumps. One point in favor of this view is the fact that it is extremely difficult to extract the fat from milk by shaking it with ether, Avithout the previous addition of alkali or acetic acid; and also that, if it is extracted without sxich addition, the liquid is not perfectly clear, but still looks turbid and almost opaque. It is at present generally believed that the butter is simply eiimlsified. This emulsion is a particularly i^erfeet one, however, owing to the supended casein, which, in the absence of the fat, would itself makes the milk more or less opaque. According to this theory, the action of the alkali or acid is not to dissolve up the bags from the fat globules, but simply to thin down the casein and alter its emulsifying power. Adulterations of Milk.— Of the various substances that have been mentioned as actual or jjossible adulterants of milk, but few ai"e met with in practice. Sometimes we find samples of milk to which some chemicals have been added as preservatives. Salicylic acid is occasionally used for this purpose, but usually either carbonate of soda or borax is employed, the latter not only acting as an alkali to neu- tralize the lactic acid, but having some slight antiseptic proper- ties as well. These latter substances are readily detected, on analysis, by igniting a measured sample of milk and noticing the weight of the a.sh. -The two coiinnon ways, however, of falsifying milk are, first, by skimming, and second, by the addition of water. The sale of skinnned milk instead of whole milk is particulai-ly ITS MEDICAL CHEMISTRY. objectionable. It not only deprives milk of a valuable constit- uent, but, which, is of more importance, it usually delays the de- livei'y of the milk at least twelve hours and frequently more, thereby greatly increasing the danger of decomposition. The addition of water, which is exceedingly common except- ing where close supervision is kept by the proper authorities, is a fraud indeed, but is less dangerous to health. In some few cases, however, the use of contaminated water for adulteration and even, innocently, for washing the cans, has caused outbreaks of typhoid fever and other diseases. THE TESTING OF MILK. The method to be employed will depend on the object for which the tests are made, whether for the municipal regulation of the milk traific or for the determination of the comparative quality of a sample of milk, as, for instance, in the clinical exam- ination of the milk of mothers and nurses. The Municipal Regulation of the Milk Traffic. — In this ease the inspector must obtain results that will enable him to appear as a witness against the dealer, and establish the fact that the milk is not the unadulterated product of the cow. This conclu- sion is best reached by examining the samiDle with a specially constructed specific-gravity instrument, or hydrometer, known as the lactometer. The Lactometer.— Hh.e two fixed points on the scale of this instrument are the 0° mark, which is at 1.000, the sf)ecific gravity of pure water, and the 100° mark, which is set at 1.029, the mini- imim gravity of milk. The graduations are continued to 120° and 130°. The point 1.029, which was long ago fixed in Europe as the limit of the density of genuine healthy milk, was redeter- mined, in 1875-76, by the health authorities of New York and New Jersey, from actual experiments at the dairies. Out of 1,G00 cows whose milk was examined, only six, two of whom were sick at the time, were found to give milk below that figure. Of late years, owing to the introduction of cattle which, by special feeding, can be made to give large quantities of very poor milk, the number of specimens of milk below this standard has increased. But such milk is also below any standard that has yet been introduced, and THE LACTOMETER. 179 is still so rare that it is never found in canseontaininf,' the mixed milk of several cows. Hence it is still the truth that a sample of milk taken in the city, which stands at less than 100' on the lacto- meter, cannot be genuine cow's milk. But besides the specific gravity, the examiner is expected to notice both the color and the consistence of the liquid as it drops from the lacto- meter on taking it from the milk. The bullj of the instrument is filled with shot, which furnish a black background for the thin film of milk; and, with a little practice, even an ill-educated person can use the instrument correctly. Genuine milk stands above 100\ gene- rally from 105' to 120°, and is ojjaque and of good consistence. . Skimmed milk is heavier than whole milk, and hence will stand even higher on the lactometer. It is distinguished, however, by being thin and watery. Watered milk will have a light spe- cific gravity, and, if it is watered enough, will stand below 100° on the scale, and be at the same time thin and watery. Cream will also stand low on the lac- tometer, but will at once be recognized by its color and consistence. Moderate skimming or watering, of milk originally of good quality, cannot be detected by this or any other known metliod ; but when the watering has been so great as to lower the specific gravity even 1° below the 100° mark, the milk can be condemned with confidence, upon the evidence of this instrument alone. The great advantage of this te^t lies in the fact that not only can the quality of the milk be accurately determined, but also that the instrument is cheap, and the test can be easily and rapidly made by the farmer, the dealer, the inspector, or the consumer. 13 Fig. 7. — The Lactometer. 180 MEDICAL CHEMISTRY. Owing to the fact that cream is Hghter than milk, it has been suggested that milk very rich in cream would therefore be light, and be liable to be condemned by the lactometer. This objection might have some basis if the cream were added to ordinary milk. But apart from the fact that in New York, at least, it is not customary to adulterate milk with cream, the lac- tometer does not only show the Aveight but also the color and consistence of the milk, and one glance at the bulb, after the in- spector had withdrawn his instrument, would at once prevent such a mistake. Natui'al rich cow's milk, however, like that from the Jersey cattle, for instance, is, as a rule, not light but heavy. For it is rich not from an excess of fat only, but from a diminution in the amount of water ; and the increased quantities of casein and sugar more than counterbalance the loss of weight due to the cream. Quantitative Analysis. — This method is often resorted to in order to determine adulteration, but it at once introduces a new set of diflficulties. The composition of genuine milk is just as variable as its specific gravity, and it is even more difficult to establish a natural minimum for each of the different constitu- ents. In fact, it is found necessary, where analysis is depended upon, to fix the minima by law. Many States have fixed the minima at 12% for the solids left on evaporation, ^% of which must be fat. Other States have put the total solids at 11.5, 13.5, or even 135^, the fat at 2.?, 3.5, 3.66, or 4;^, and the ash at 0.60 or 0.701 There is also considerable difference of opinion as to the most reliable methods of analysis, and the results obtained by various analysts, working with different methods, rarely coincide. A very serious objection to analysis is the fact that the test cannot be made on the spot, but must be executed in the labora- tory, by a skilled chemist, using expensive apparatus and with the expenditure of a good deal of time. This raises the cost of the test above the value of the milk, so that neither producer nor dealer can afford to have it made, while the delay in obtain- ing the results robs the inspection of much of its force. If a par- ticular .sample should have a composition below the legal limits, Ihe milk has still been disti'ibuted among the consumers; while CLINICAL TESTS FOR BREAST MILK. 181 if the milk is shown to be watered by the lactometer, it can and should be poured into the gutter at once. In the case of skimmed milk, however, where tlie liquid, although standing well above 100° on the lactometer, looks suspiciously thin and blue, it is often advisable for the inspector, before condemning the sample, to have his suspicions confirmed by analysis or, although less accu- rately, by the cream test. The Ferctntage of Cream.— It has often been suggested that the quality of a sample of milk could be determined by noting the amount of cream that rises in a given time. This can be easily done by letting the milk stand over night, or for twenty- four hours if necessary, in a graduated cylinder. This method unfortunately, although often useful, especially when made in connection with the specific-gravity determina- tion, is too unreliable for municipal inspection. The cream from different kinds of cow's milk differs very much in consistence and in composition, and a milk containing but little fat may actually furnish more cream than milk containing twice that amount. This will be seen at once from the following examples, given by H. Schroeder: Samples No. 1. Fat, ZM% Cream, 21. % Other TV.vte.— Various tests have also been suggested which depend solely upon the color or the opacity of the milk to be ex- amined. It is, of course, a fact that the appearance of the milk varies with the amount and quality of the cream, and, to a slight extent, with the quantity of casein contained in it. But while it is possible to distinguish in this w^ay a sample of watered milk from cream, or of skimmed milk from good whole milk of the same specific gravity, the difference between individual samples of whole milk and watered milk is so slight that no sharp dividing line can be made between them. Clinical Tests for Breast Milk. — This very interesting subject has, until very recently, received almost no attention in this country, although it is of great importance in connection with the digestive disorders of nurslings. It is Avell known tliat no artilicial food, however carefully pre- 2. 3. 4. 5. 6. 4.87 4.09 5.38 3.13 4.09 16. 10. 10. 12. 13. 183 MEDICAL CHEMISTRY. pared, ean quite take the place, for young infants, of the mother's milk. Yet in case after case it happens that the milk, for some reason or another, does not agree with the child, and hence that a new nurse must be obtained, or else that the child must be weaned and brought up by hand, often with considerable risk. Careful investigation has shown that when the milk disagrees with a child, there is almost always some decided variation in the composition. The percentage of sugar usually remains about the same, but the fat and the casein vary considerably in the milk from the same woman, with the condition of the nervous system, and also with changes of diet, exercise, or of general hy- giene. When these variations are recognized, it is often possible, by regulating the food and controlling the other conditions affect- ing the mother or nurse, to restore the milk to its normal compo- sition, and thus remove the cause of disturbance. The iDractical importance of this can hardly be over-emphasized. It is not necessary, for this purpose, to have always a com- plete analysis of the milk. According to Dr. L. Emmett Holt, of this city, who has studied the question very thoroughly, the in- formation given by the specific gravity and the percentage of cream is sufficient to determine any serious changes. The specific gravity of normal breast milk varies usually from 1.028 to 1.033, averaging about 1.031; while the cream which rises in twenty- four hours, corresponding to the normal average of from 3 to 44/'? of fat, should keep within the limits of from 6 to 9^ or so. The following table will he\i> to explain the results of the examination. It will be noticed that the casein and the fat vary independently of each other : Human milk. Specific gravity. Cream In 24 hours. Proteids (calculated). Normal average 1 .0.31 (70° F.) 7.5 to 8..5 ^ 1 .5 to 2 ^ Healthy variations 1.028 to 1.029 9 to 12^ normal (rich milk) " 1.032 to 1.0.33 5 to 6^ " (fair milk) Unhealthy " below 1.028 high (above 9 jJ) normal, or slightly below " " " " normal (G to 9;^) low " " " " low (below G^) very low (very poor milk) " " above 1.033 high very high (excessively rich) " " " " normal high " " " " low nearly normal The specimen for examination should be either the entire product of one breast, or taken after the breast has been about one-half emptied. KOUMYSS. 183 By using specially constructed hydrometers, and by deter- mination of the cream in 10 c.c. graduated cylinders, the quantity of milk needed is reduced to a minimum. KOUMYSS, This is the general name given at present to any fermented alcoholic beverage made from milk. History.— Its preparation and use have been introduced from the plains of southern Russia, where the various Tartar tribes, for many hundred years, have been accustomed to employ it, not only as a stimulant, but as a food. Preparation.— Originally it was always prepared from mare's milk, but nowadays it is usually manufactured from cow's milk, skimmed and generally sweetened so as to resemble the other more closely. To produce the alcoholic fermentation in milk- sugar a peculiar ferment must be used, the kor or kefir ferment, the original of which came from the Steppes. This occurs as small irregular-shaped grains about the size of a pea, with a peculiar chocolate-like odor. It seems to contain, besides two forms of the ordinary yeast plant, a peculiar baciUus (Dispora caucasica), the whole cemented together with a sort of gummy material. It is supposed that by the action of the bacilli the lactose is converted into the glucose galactose, which then under- goes alcoholic fermentation in the ordinary manner. Composition,— Besides the alcohol and carbon dioxide result- ing from this, koumyss always contains some lactic acid from the action of some of the ordinary bacteria, and also traces of butyric and acetic acid. The casein is first coagulated by the acid, and then broken up into fine particles by the agitation which is a necessary part of the process of manufacture, while some of it seems to be actually decomposed into albumoses or similar bodies. Uses.— Koumyss is very largely used at present as a food .stuff, in cases of malnutrition or of wasting disease. It has a not un- pleasant, sour, rather pungent taste, which to many people is extremely palatable; and besides acting as a slight stinu^lant, owing to the presence of carbon dioxide and small quantities of alcohol, it furnishes the constituents of milk in a very digestible form. 184 MEDICAL CHEMISTRY. Analyses. — The following analyses of koumyss, given by KOnig,* may be of interest : Koumyss from Mare's Milk, 43 Analyses. Lactic Nitrogenous Alcohol. Acid. Sugar. Matter. Fat. Ash. Minimum, 0.15 0.34 1.12 0.80 0.28 Maximum, 3.29 2.92 6.80 3.73 2.56 0.77 Average, 1.91 0.91 1.77 2.24 1.46 0.42 Koumyss from Cow's Milk. Average, 1.14 0.55 4.09 2.66 1.88 0.48 Koumyss from Skimmed Cow's Milk. Average, 1.38 0.82 3.95 2.89 0.88 0.53 LABORATORY EXPERIMENTS. MILK AND KOUMYSS. I. Cow's Milk. — 1st. Specific Oramty. — Test some skim milk with the urinometer, and notice that it stands at about 1.033. Use this milk for the tests 2d, 3d, and 4tli. During the lesson make comparative tests with the lactometer on whole, skimmed, and watered milk and on cream, noticing the reading on the scale, the appearance of the liquid on the bulb, and the way in which the liquid drijjs on lifting out the instrument. Also place a drop of each under the microscope and observe the comparative abundance of the fat-globules. 2d. Casein. — Put some skim milk in a test-tube, add a little HNOa dil., and notice the coagulation of the casein. Warm the rest of the skim milk in a beaker on a water bath to 38° or 40° C, add a few drops of rennet, and let it stand quietly until it coag- ulates. Cut the curd with a knife, and decant or filter off the whey for Te,sts 3d and 4th. Test the casein : (a) With the xantho- proteic reaction, (h) With Millon's reagent, (c) Warm gently on the water bath with HCl cone. = violet colored solution. • Loc. cit., pp. 418-419. MILK AND KOUMYSS. 185 (cZ) Warm with water and a few drops of KOH = solution. Reppt tlie casein from this solution by neutralizing it with very dilute HCl, or better, dilute acetic acid. 3d. Milk ^ugar, Lactone.— Teat the whey for lactose: (a) By Moore's test, {h) By Trommer's test, (c) By Fehling's test, (d) By the picric-acid and potash test. For the details of those tests see Lesson II. 4th. Inorganic Constituents.— Vnt the rest of the whey in a small evaporating-dish, add a few crystals of NalsOs, and evap- orate it gently over a small flame, stirring it constantly. When it gets down to dryness, heat it cautiously until it ignites with more or less spattering, and, after that, heat it strongly until most of the organic matter is burnt white. Let it cool, add a little water and HNO3 dil., warm gently, and filter. Test the solution in separate test-tubes : (a) For j^/iOA'/j/iaies— with excess of (NH4)2Mo04. {b) For chlorides— \i\.i\\ a drop or two of Ag^'03. (c) For suljihates— with, a drop or two of BaCh. The tests (b) and (c) will probably be very faint. 5th. Butter Fat.—Vnt the cream into a small evaporating- dish, add an equal amount of alcoholic potash solution, and heat over the water bath for some time. Notice the characteristic smell of butyric ether. Then add a few drops of dilute H^SOj, and notice that the same smell becomes more distinct. Compare this with the butter tests in Lesson VII. II. Clinical Tests on Breast Milk.— Whenever it is possible the student will be provided with a small sample of breast milk. It should be examined as follows : (a) Specific (?;tnvY?/.— Determine the specific gravity accu- rately by means of the small clinical hydrometer (to be obtained from the demonstrator). Q)) Percentage of Cream.— Stir the milk carefully and then fill up to the zero mark the 10 c.c. graduated cylinder on your desk. Let the milk stand for twenty-four hours; then examine it and note carefully the percentage of cream. . Calculate, from the figures thus obtained, the probable pro- portion of the constituents of the milk, according to the directions given on p. 183. 186 MEDICAL CHEMISTRY. III. Koumyss.— Examine some koumyss as follows : 1st. Carbonic-Acid G^as.— Notice how, when the liquid is poured into a beaker, the escaping gas will extinguish a burning match. 2d. Taste it and smell it. 3d. Reaction.— Notice that it has an acid reaction to test paper, due to the presence of lactic, butyric, and perhaps acetic acids. 4th. Casein.— Hesit the koumyss gently, in a beaker, till it begins to boil. Cool, separate the coagulated casein as much as possible from the whey, and filter enough of the latter to serve for Tests (a), (&), and (c). The tests for lactose can be made on unfiltered whey. Test the casein as above, under Milk. If you have time test the filtered whey as follows : (a) Alcohol. — Fill the flask not over one-quarter full, add a piece of pumice stone, and distil over very carefully into a test-tube, as in Lesson V. Test the distillate for alcohol with the iodoform and with the molybdic-acid tests. For the details of these tests see Lesson V. (&) Butyric Acid.— Tefit the same distillate for butyric acid: 1st. By the smell. 2d. With test paper = acid. 3d. Add a few drops of common H2SO4 and shake = char- acteristic odor of butyric ether. (c) Dissolved Froteids.— Test the filtered whey for these by the xantho-proteic and the biuret tests {v. Lesson VIII.). (d) Lactose. — Test the whey for lactose, as above under Milk. Microscopical Examination. — Examine carefully a drop of koumyss under the microscope. Notice the fat-globules floating on the top, the yeast cells lying on the bottom, and the innum- erable bacteria floating all through the liquid. Notice also the comparatively large lumps of casein scattered through the mass. LESSON XIX. THE BLOOD. Blood may be briefly described as a thick, viscid fluid, which circulates during life through all the tissues of the body. Its functions are varied and of the greatest importance, for it really serves as the sole medium of counuunication between the interior of the body and the outside world. It carries oxygen, and also nourishment of all sorts, to every part of the body, and removes all the waste products which would otherwise prove extremely injurious. It serves to keep the body temperature uniform, and to keep all the joints and tissues moist and in good condition; while some of its constituents are of great service in warding oflf the germs of disease, and inrepamng and building up the tissues where lesions have occurred. Besides this, the blood is the source from which all digestive fluids, and also all the secretions and excretions of the different glands and organs, are originally derived. It is interesting to notice how the same blood plasma is converted, by the action of cells, into such a range of fluids, with such different properties and functions, as the gastric and pancreatic juices, saliva, bile, milk, lymph, urine, and the many others which might be men- tioned. GENERAL PROPERTIES. In man and in the higher animals blood is a red opaque fluid, owing both its color and its opacity to the enormous quantity of minute corpuscles suspended in it. During life we may consider it as composed of the thick, yellowish liquid known as plasma, and the blood cells, both red and colorless. When taken from the living blood-vessels, the blood coagulates, i.e., some of its constituents are converted into the insoluble compound fibrin, which, when undisturbed, enfolds all the corpuscles within its 188 MEDICAL CHEMISTRY. meshes, forming "what is known as a clot and expressing a trans- parent, yellowish fluid, the serum. By manipulating a clot of blood, we can press out the blood cells into the serum and extract the fibrin by itself, thus jiroducing defibrinated blood, a fluid very similar in most of its i^roperties to the blood in the body. Specific Gravity. — The si^eciflc gravity of human blood varies from about 1.040 to 1.075, the average being, for men, 1.058, and for women, 1.055. It varies more or less with age, and also with the amounts of food, drink, and exercise, the external tempera- ture, and similar conditions. It is diminished, only temporarily, however, by hemorrhages. Quantity. — The quantity of blood is usually about one-thir- teenth of the body weight, and this, as well as the specific gravity, is kept within rather close limits by the kidneys, skin, and pos- sibly the liver, spleen, and other organs. Taste and Odor. — Blood has a rather insipid taste, due proba- bly to the alkaline salts contained in it, and it has a distinct though faint odor which is quite characteristic of the animal from which it is derived. The odor is brought out much more distinctly by the addition of a little concentrated sulphuric acid, which sets free traces of volatile acids which have a more pro- nounced smell than the salts from which they are derived. Reaction. — The reaction of blood is slightly alkaline, depend- ing upon the presence of hydro-disodic-phosphate, and possibly of a little sodic cai'bonate. After shedding, the alkalinity dimin- ishes, and on coagulation the blood becomes acid and increases in acidity as it stands. It is a matter of some difficulty to estimate accurately the amount of this alkalinity. Careful experiments, however, by Von Jaksch and others, tend to show that it is often diminished in fever, and always in uraemia, liver disease, diabetes, and some other disorders. It is also diminished in rheumatism and in a gouty condition of the body, and one author, Cantani, insists that he has found it actually acid, during life, in the last stages of cholera. This, however, is exceedingly improbable. Color.— The color of the blood is due to haemoglobin, the color- ing matter contained in the red corpuscles. The serum and plasma are both colored yellow or orange, and the individual COMPOSITION OF THE BLOOD. 189 corpuscles, when seen under the microscope, have but a faint yellowish tinge which changes to red only when several of them are supor[)0.sed. In natural blood the hemoglobin is contained in the blood cells only, and this makes the liquid thoroughly opaque. It is possible to extract the hjemoglobin from the corpuscles and cause it to dissolve in the serum, when the colorless body, known as the stroma, which forms the remainder of the blood cell, no longer interferes with the light, and we have a dark red, transparent solution. This is the case when blood is heated up to about GO" C, or is rapidly chilled and heated, or is subjected to electric sparks. The haemoglobin can also be dissolved out by an excess of water, or by the admixture of chloroform, ether, alkalies, strong acids, and numerous other reagents. On the other hand, the addition of solutions of neutral salts, such as XaCl. Na^SO^, and others, tends to shrivel up the l)lood cells, which retain firmly their coloring matter, and the result is a very opaque fluid with a bright vermilion color. The difference in color between the arterial and venous blood is due to another cause, the presence of the hemoglobin in the oxidized and in the reduced condition. COMPOSITION. According to several analyses by Sacharjin and Hoppe-Seyler,* healthy horse's blood contains, on an average, in 1,000 parts- Blood corpuscles, 344.18 parts, of which about 213 parts are solid material and 131 " " water. Plasma, Go5.82 parts, of which about 593 parts are solid material and 62 " " water. These figures would probably not vary much in the case of normal human blood. "With regard to the general composition of fresh human blood the following analyses are interesting. They were made by Bec- querel and Rodier,t about 1844, upon specimens of blood from * Hoppe-Seyler, "Physiol. Chem," 1881, Part II.; p. 447. t Quoted by Hoppe-Seyler, "Physiol. Clieni.,"' p. 471; also by H. VIerordt, "Auatom. Physiol, u. Physikal. Daten u. Tabellen ;" Jeua, 18S8. 190 MEDICAL CHEMISTRY. eleven males and eight females, all adult and in fairly normal condition. The amount of hfemoglobin was calculated by Hoppe- Seyler from the percentage of iron. Males. Females. "Water, .... 779. 791. Solid materials, 221. 209. The latter were composed of Fibrin, 2.2 2.2 Haemoglobin, 134.4 121.7 Proteids, 76. 76. Cholesterin, lecithin, and fats, .... 1.6 1.62 Extractives and salts, 6.8 7.4 Hsemoglobin. — This, the red coloring matter of the blood, may be considered as the most important of all the constituents in the above table, for it furnishes the means by which the blood carries oxygen from the lungs throughout the body. Occurrence. — It occurs to a minute extent in the muscles of the higher animals, but it is practically all contained in the red blood cells of which, when dry, it forms, in man, from 805^ to 90^ by weight. The remainder of the corpuscle, known as the stroma, is a colorless, spongy mass, composed of albuminous matter Avith small amounts of cholesterin and lecithin. It is supposed to hold the haemoglobin within its pores, perhaps in a state of loose chemical combination. The coloring matters from the blood of different animals have the same general properties, but are sufficiently different in crys- talline form, solubility, and chemical composition to show that they are not absolutely identical. Preparation. — Hsemoglobin, in its oxidized condition, may be extracted from blood in several ways. From the blood of a rat or a guinea pig it readily crystallizes out, after a little standing, upon the simple addition of a few drops of water. When dealing with the blood of other animals, it is usually necessary to sepa- rate the red Ijlood cells by centrifugal action or by settling, and then to decompose tliem with ether, letting the coloring matter slowly crystallize from the lakey solution. Properties. — The oxy-hsemoglobin, extracted in this way, is in the form of dark red crystals, containing from 3 to % of water of crystallization. Most varieties of it dissolve but slig'itly in water, HEMOGLOBIN. 191 and not at all in alcohol, ether and chloroform. It is somewhat soluble in dilute alkalies. The solutions are red by reflected, but green with transmitted light. Composition. — The composition of the different varieties of haemoglobin has been very carefully studied. According to some very careful analyses by Hoppe-Seyler,* the oxy-htemoglobin from dog's blood is composed of — C H N O S Fe 53.85 7.33 10.17 21.84 0.39 0.43;^ Of all the constituents mentioned above, iron is the charac- teristic one, giving the comijound, it is believed, its power of absorbing oxygen. It is contained in human haemoglobin to the extent of 0.42;^, and thus furnishes an easy method for calculating the percentage of ha;moglobin in any sample of blood. In this way we find that the average amount of haemoglobin in human blood is from 13 to 15,'?, being somewhat less in women than in men. In cases of ansemia from various causes, this per- centage of haemoglobin may be reduced nearly one-half. Special Ijieces of apparatus have been devised both for counting the number of blood-corpuscles and for determining the jiercentage of haemoglobin, more or less accurately, for clinical purposes. These have proved of much value, not only for diagnosis, but also for following the course of the disease. Action of Oxxigen. — The oxy-haemoglobin just described is a loose chemical combination of oxygen with haemoglobin itself. The latter can be obtained from aqueous solutions of the former by exhausting under a vacuum, or by reducing with a stream of hydrogen, or, more conveniently, with an alkaline solution of ferrous hydrate. In each of these cases the oxygen is extracted, leaving a solution of haemoglobin. This same result takes place in the tissues, where the bright red arterial blood containing the oxy-hicmoglobin is reduced to the dai-ker colored venous blood. Pure or reduced haemoglobin can also be crystallized, though with difliculty, and is somewhat less soluble than the oxidized form. It absorbs oxygen very readily, even on standing in the air, in the proportion of I.IG c.c. of oxygen, at 0' C, and a pres- * Iloppe-Seyler, " Medicin. Cliem. Urulersuch.," 186G-71; p. 3T0. 192 MEDICAL CHEMISTRY. sure of one metre of Hg, for one gramme of the coloring mat- ter.* Methsemoglobin. — There is anotlier compound of haemoglobin with oxygen, called methcemogiobin, which is a more stable com- pound than the other, and has a brownish color when in solution. It is produced by slow oxidation, and hence is found in old blood stains, and sometimes in bloody urine, bloody cysts, and the like, where some time has elapsed since the effusion. It can also be prejDared directly by oxidizing haemoglobin with chlorate or per- manganate of potash and other oxidizing agents. H8em,atin. — When aqueous solutions of oxy-haemoglobin are heated, especially in the presence of either acids or alkalies, it readily decomposes into a proteid of the globulin variety and about 4% of the red coloring matter haematin. Small quantities of carbon dioxide and volatile fatty acids are formed at the same time. Haematin is a bluish-black, amorphous body, insoluble in water and alcohol, k>ut soluble in dilute acids and alkalies. Its comi3osition, according to Nencki and Sieber,f corresiDonds very closely to the formula C32H32]N'4Fe04. Its most interesting deriv- ative is haemin, a compound of haematin with two molecules of HCl. Haemin. — This substance is formed whenever nascent HCl is allowed to act upon a body containing either haemoglobin or some of its derivatives. It forms extremely characteristic microscopic crystals, dark in color, and shaped like httle rhombic plates or rods with sharp angular ends. When formed from minute quan- tities of blood they are very small, needing careful examination under a one-sixth objective. They are quite insoluble in water and dilute acids, but dissolve readily in alkalies. Fibrin. — The formation and properties of this substance have been discussed in Chapter III. The Serum.— This is the rather thick, transparent, yellowish or brownish fluid that is expressed from the clot when coagulated blood has stood quietly for some hours. It is blood after the re- moval of both fibrin and corpuscles. It contains, all told, from 8 to 10^ of total solids, of which 6 to * HUfuer, Zeitsch. Phys. Chem., I., 1877-78; p. 388. + Berichte, xvii, '84; p. 8,270. SPECIAL TESTS FOR ALBUMIN. 193 S% are proteids, and the rest are fat, salts, and minor constituents. Of the proteids the only two that have been so far isolated are serum albumin and paraglobulin, both of which have been de- scribed before. These are contained in varying proportions in the blood of different animals, human serum, according to Ham- marsten,* containing on an average, 4.5% of albumin and 3.1% of paraglobulin, and bullock's serum, 3.3,':^ of the first and 4.2% of the latter. In the body we rarely find one without the other, and, as their significance is the same, the tests that we use for finding alljumin in the urine and other fluids of the body are such as to include paraglobulin also. Still, it is possible to separate the latter from the serum albumin by saturating with CO:, or with MgSOi. Special Tests for Albvimin (and Paraglobulin). — The tests de- scribed are, on the whole, the most satisfactory when testing for small amounts of albumin. They will be mentioned again under Lesson XX III. The iirst of these tests, the addition of acetic acid and then boiling, is in very common use among physicians, and, while it works somewhat better in urine than in solutions of pure serum, it is on the whole eminently itnsatisfactory. As will be noticed in this lesson, the slightest excess of acetic acid will spoil the test by forming the soluble acid albumin on heating. If, however, too little acid is added, the solution remains slightly alkaline, and the albumin does not i)recipitate, because it is changed into alkali albumin. The next test, with acetic acid and potassic ferro-cyanide, in the cold, will be found more satisfactory. The modification where a ring is formed is particularly delicate. The ring test with nitric acid, or Heller's test as it is often called, is, on the whole, the most satisfactory of them all. In our lessons the student is directed to use dilute nitric acid. The test is usually made with concentrated acid, and is then a little more delicate; but is more liable to error than in our method, because the strong acid may precii)itate uric acid when used on a sample of urine. The test shows readily the presence of one part of al- bumin in 40,000 or 50,000 parts of water. * Pfluger's Arch., 17; p. 4bd. 194 MEDICAL CHEMISTRY. The ring test with picric acid is not quite as delicate as the last test, chiefly because the solutions are so nearly alike in den- sity that it is hard to prevent them from mixing. The great ad- vantage of tills test, however, is that, after testing for the pres- ence of albumin, the same solution, with the addition of some potash, serves also for determining the presence of glucose. Paraglobulin. — This proteid has already been described in Lesson III. The separation of it from serum by means of CO2 is not at all perfect unless the gas is allowed to pass through the liquid for some hours. Enough, however, for our test can be extracted in fifteen or twenty minutes. Fats. — There is always a small amount of fat present in the blood, probably in a very finely emulsified condition. Its per- centage varies greatly, accordingly to the food and condition of the individual. In the serum of fasting animals it is about 0.2%, while after a meal rich in fatty food it may run up as high as 1.25^. In the latter case the serum is often more or less milky. Besides the ordinary neutral fats, small quantities of eholesterin and lecithin and, perhaps, of fatty acids are also present. LABORATORY EXPERIMENTS. BLOOD. I. Odor. — Put half an inch or so of blood in a small beaker and add a few drops of common HqSOi. Mix the two liquids and notice the peculiar odor of the blood. II. Haemoglobin. — Fill the bottle half full of a solution of de- fibrinated blood in 20 or 25 volumes of water. Then make up a " reducing solution " as follows : Put in a test-tube half an inch of a strong solution of FeSOi, add the dry tartaric acid, and enough NH4OH to make a clear dark green mixture. Add a little of this reducing solution to the blood in the bottle, and notice that the color changes to a. darJc purple = reduced haemoglobin. Shake this up three or four times in the bottle with air, and notice that it becomes red = oxy-hsemoglobin. Reduce this again with the reducing solution, and again oxidize it by shaking. FIBRIN— MIXED PROTEIDS IX BLOOD. 195 Mix some blood in a beaker witli 25 or oO volumes of water, and notice that the blood dissolves, becoming "lake-colored," i.e. dark and transparent. Mix some blood in another beaker with the same volume of 10% NaCl solution, and notice that the color changes to a bright vermilion and that the solution remains opaque. Examine under the microscope a drop of each of these last mixtures, and notice that in the first the i"ed corpuscles are almost invisible, while in the second they are plainly seen, although much shrivelled and contorted. III. Fibrin. — J^otice the structure of fibrin, both dry and wet. Test the wet fibrin as folloAvs : 1st. Xantho-proteic I'eaction. 2d. Millon's reaction, with the addition of a little water. 3d. AVarm with some diluted KOH in a test-tube on a water bath = solution. 4th. "Warm with some H(J1 cone, in a test-tube on a water bath = violet-colored solution. 5th. Warm with some acetic acid = a gelatinous mass. IV. Mixed "ProtGidiS.— General Tests. — Fit a thermometer to a test-tube containing some undiluted serum. Heat very gently in a large beaker of water, and notice the temperature of coagula- tion, about 7G" C. Dilute some serum with four or five volumes of water. To some of this add one drop of very nmch diluted acetic acid, HCaHaOa, and repeat the above test. (There Avill probably be an opales- cence at about G3 to 06^ C, and coagulation at about 80' C.) Make the following tests on the diluted serum : 1st. Millon's test. 2d. Xantho-proteic test. Notice that the addition of HXOa, even if dilute, to diluted scrum will cause a i^pt. 3d. Add alco- hol = ppt. 4th. Add HgCU = ppt. Special Tests.— Ui. Acetic-Ae/d and Heat Tesi.—Fm a test- tube nearly full of diluted serum, and to this add a drop or two of much diluted HC2H3O0. Heat the top part of the mixture and notice the white ppt. or cloud. Notice that the least excess of acid spoils the test. Also notice that the resulting ppt. does not dissolve on the addition of some dilute HNO3. 2d. Acetic-Acid and Ferrocyanide of Potash Te*^.— Fill a test- 14 196 MEDICAL CHEMISTRY. tube half full of diluted serum, and to this add half an inch of HC2H3O0, not diluted, and a few drops of potassic ferrocyanide, K4FeCy6. Xotice the white, floeculent ppt. Repeat this test as follows : Put in a small test-tube half an inch of a clear mixture of HC2H3O2 with a quarter of its bulk of KiFeCye. To this, down the side, add very gently, through a pipette, a little diluted serum. Notice the white ring whei*e the liquids meet. 3d. Nitric-Aeid Ring Test. — Put in a small test-tube half an inch of HNO3 dil., and to this, down the side, add very gently, thi'ough a pipette, a little diluted serum. Notice the white ring where the liquids meet. 4th. Picric-Acid Test. — Put in a small test-tube half an inch of picric-acid solution, and to this, down the side, add very gently some diluted serum. Notice the white or yellowish ring, and, on mixing the liquids, the ppt. N.B. — These last tests are those used in testing for albumin in urine. It is therefore very important to make them repeatedly with more and more dilute solutions of serum, and to compare carefully their resjiective accuracy and delicacy. V. Paraglobulin. — Dilute some serum with eight or ten vol- umes of water, and pass through it, in a beaker, a stream of CO2 gas, made by adding HCl dil. to some limestone in a flask with a delivering-tube. Notice the formation of a white turbidity = paraglobulin. Let it settle for a few minutes, filter off the white ppt., wash it with water, and dissolve it on the filter into a test- tube with a few drops of \% NaCl solution. Test this solution carefully for paraglobulin Avith the biuret test. YI. Fats.— Add half an inch of gasolene to a test-tube half full of serum, and shake vigorously. Let the gasolene rise to the top, and test it for dissolved fatty substances as follows : 1st. Put a drop on some warm water in a watch-glass. Let it stand a minute or two for the gasolene to escape, and then exam- ine it, under the microscope if necessary, for globules of fat. 2d. Soak up the rest of the gasolene with a piece of filter paper. Let it dry, and notice the greasy appearance and touch of the paper. LESSON XX. BLOOD (CONTINUED) AND BILE. INORGANIC CONSTITUENTS OF BLOOD. These consist of the same acids and bases aheady tested for when examining the ashes of bone, of milk, and also of wood. The total quantity of mineral matter in blood varies from 0.8 to 1.3/?. It consists ijrincipally of sodium chloride, with smaller quantities of sodium and potassium phosphates, sulphates, and carbonates, and traces of lime and magnesia salts. The iron present is due almost entirely to the hiemoglobin in the red cor- puscles, but faint traces are also found in the pure serum, prob- ably in the yellow coloring matter, which strongly resembles lutein. BLOOD STAINS. We must now say a few words about the tests by which we are enabled to determine the presence of blood in spots and stains. There are usually two questions Avhich it is important to have answered in such cases : 1st. Whether the stain is blood or not, and 2d. Whether the stain is human blood. Haemin Test.— The first of these questions can be satisfactorily answered by this test, which, if properly made, is extremely deli- cate and perfectly accurate. It depends upon the formation of crystals of lucmin (described on page 187), by the evolution of nas- cent hydrochloric acid in the presence of the suspected material. This HCl is produced by the action of hot, concentrated, acetic acid upon a few crystals of common salt. Only minute quanti- ties of the suspected material need be used, a thread or two of the stained cloth, or a few granules of dust or scrapings from a suspected spot, being all that are required. To obtain satisfactory results with this test, the experimenter must observe certain precautions. He must not add too much 198 MEDICAL CHEMISTRY. salt, four or five small crystals being quite enough; he must use the strongest kind of acetic acid ; he must be sure that the mixture fairly boils; and, most important of all, he must not mistake for haemin crystals the large, colorless, more or less irreg- ular crystals of sodium chloride, or sodium acetate, which are always present. The haemin crystals jDroduced in this test vary somewhat, in size and appearance, according to the variety of blood and the exact proportion of the reagents used. They can be generally described, however, as extremely minute, dark colored, shari^- angled rods or prisms, see Fig. 8. They can only be seen by care- ful examination of the preparation with a lens of high power. This test possesses two or three important advantages over the others described in this lesson. It can always be obtained, by careful manipulation, from any kind of blood stain, how- ever old and however dried up. Besides this, there is no stain that we know of, excepting blood, which will j^roduce similar crystals. The chief, if not the only, disadvantage is that it is not always easy to exhibit these crj^stals, under the microscope, to an average jury. This objection, however, can be partly overcome by the aid of photography. Examination for the Blood Corpuscles. — The heemin test gives us no idea as to the source of the blood. The only chance of finding that out is to examine the stain under the microscope, in the hope of identifying the individual corpuscles. This is a matter of very considerable difficulty. After only a few hours' drying, the corpuscles shrivel up and become indistin- guishable, so that from the examination of a dry stain no results at all can be obtained. The only way to bring the cori^uscles back to at all their original size and shape is to moisten them very carefully with glycerin, or with a 0.2;? salt solution, or with some other liquid which has as nearly as possible the specific gravity of the original blood plasma. Even in this case it is very rare to find a corpuscle in at all a perfect condition. If they arc moistened with water or with some other light liquid, they swell up very much and finally burst; while if the liquid is too heavy, they are shrivelled all out of shape. Plate IV. Fig. 1. Human Blood-Corpu.scles, x ll.W; average diameter = 0.000327 inch; lines = 1-5000 inch. From microphotof^raph by Ur. J. J. Woodward, U.S.A. FlO. 3. Dog's Blood-Corpusele.s, x ll.iU: avei-ntrc dianietor _ (t D00S40 inch, lines ^ 1-5000 inrli. From microphoto^rnph by Dr. J. J. Woodward, I'.S.A. EXAMINATION FOR THE BLOOD CORPUSCLES. 199 It is best not to look for the blood corpuscles in the middle of a great mass of blood, but to examine on the outskirts of a small stain, where only two or three corpuscles probably settled origi- nally. This is especially the case when the stain is adhering to a fibrous material like cloth. When, finally, a more or less perfect corpuscle has been found, it is necessary, in any medico-legal examination, to determine, w'ith the utmost care, not only its exact shape, but also its exact size. In any important expert case the evidence of the eye is not sufficient. The corpuscle ought to be photographed in connec- tion with the i^roper scale, so that the jury and any opposing exjjerts can have an opportunity of studying it for themselves. The shape of the human corpuscle is the same as that of all other mammalia excepting the camel family, i.e., a flat round disk, Avith a depression in the centre of each side. This depression however, can hardly ever be distinguished in a case of this sort, the corpuscle in almost every case swelling to a globular mass. The blood cells of birds, fish, and reptiles are oval, with dis- tinct raised nuclei in the centre, and hence are readily identified. But the cells of many common maiimialia not only have the same shape, but are so nearly of the same size as the human blood corpuscle that it is practically imjiossible to distinguish between them. The average diameter of the human cell is about 7.7,u * (0.0077 mm.), as against 7.3 for dog's, 6.5 for cat's, 5.9 for bul- lock's, 5.8 for horse's, and 5. for sheep's blood. Besides these common varieties, the blood cells of monkeys, guinea pigs, hares, mice, and a few other animals are very nearly of the same size as the human corpuscle. But even these slight variations in size cannot be depended upon, for the individual cells of each variety have a very consid- erable range in size. This renders it quite hopeless to identify scattered cells, even of animals whose average cells differ widely. Thus, the human corpuscles vary in size all the way from 6.4 to 8.6, a range which covers individual cells from almost all the ani- mals mentioned above. Accordingly, while in medico-legal Avork it is often possible to positively identify a given sample of blood as mammalian blood, it is impossible to ascertain, by any test as yet known, whether * Welker, Zeitschi-. f. ration. Med. (3;, xx., p. 279. 200 MEDICAL CHEMISTRY. it was originally derived from man or from a dog, and very diffi- cult to distinguish the blood of other common mammalia. The Giiaiacum Test. — This test is an interesting one, and reacts readily with minute quantities of blood, both fresh and old. The reagents used are fresh solutions, 1st, of gum guaiacum, and, 2d, of hydrogen peroxide. The gum guaiacum has the i^roperty of turning blue when in the jjresence of nascent oxygen, which, it is supposed, is set free from the hydrogen peroxide by the action of some of the ingre- dients of blood. The test is an extremely delicate one, especially if the guaiacum solution is diluted with alcohol. But it has the serious disad- vantage of being not so much a test for blood as a test for ijroto- plasm in any form. In fact it works equally well with almost any cell contents, animal or vegetable. In our lesson we exhibit its action upon potatoes, and it will also react with milk, seminal fluid, and many other similar objects. The chief value of this test is a negative one. A stain which does not react with guiacum in this manner cannot be blood. The Spectroscope. — This instrument is often used for the de- tection of blood, and, in the hands of an experienced observer, it is extremely satisfactory. The different spectra, belonging to the " absorption " or " dark band " class, produced by haemoglobin and its derivatives, are perfectly characteristic of blood, and blood only; while they can often be satisfactorily demonstrated, if nec- essary, to jury and experts. The susi^ected material ought to be carefully isolated and soaked for some hours in a few drops of water, with frequent pressing and stirring. The liquid is clarified as much as possible by straining and filtering, any coloring matter left behind in this process being carefully washed back, and then is concentrated at a very gentle heat or, better, by standing over a desiccator, until it is ready to be examined under the spectroscope in a little cell. If the amount of material taken is very minute, the solution is often evaporated to dryness in the bottom of a watch glass and the examination made upon the little film remaining. The spec- troscope should be arranged so as to throw, for comparison, a spectrum of real blood alongside of the spectrum of the suspected material. Plate V. jk T /•**'","V' Kk;. 1. Human TUood-CorptiscIis. from rlnVd stain sonki.l mit, x SIW) ; lines = I-IOPO inch. From micro I)'iUitoKraph by 1>1-. J. J. Woodward, L'.S.A. Fio. 2. Klfiiid-Coniusclc-: of Friiir. x SOO. Krcim microphotoirrapli liy .\. .1. \V w»ki>. I'.S.A. THE BILE. 201 If the stains are from fresh blood, the spectrum of oxyhjemo- globiu may be expected. If, however, the blood has been stand- ing for any length of time, the haemoglobin present will probably have been oxidized to met-hsemoglobin. The chief drawback to this method of testing is that it needs very careful maniindation, and also requires an expensive and somewhat delicate piece of apparatus. THE BILE. Occurrence.— The bile is a lluid, originating in the liver, which in part passes directly into the intestines, but most of which is first stored temporarily in the gall bladder, where it is mixed with more or less mucous secretion. Preparation. — It can be occasionally obtained through fistulse in living animals, but is usually taken from their gall bladders after death. . Properties. — («) Plty^ical. — Its character varies more or less with the species and with the individual from which it is ob- tained. In general, it is a rather thick, viscid fluid, somewhat stringy fi*om the mucin added to it in the bladder. On shaking, it forms a thick froth or foam like the lather of soap. It has a faint, aromatic odor and a characteristic, intensely bitter taste. Its color varies from yellow, orange, or brown, in the case of human bile and that from many carnivorous animals, to quite a pronounced green in the bile of many herbivora, such as sheep and bullocks. These colors, however, always intermingle more or less. When taken from the gall bladder, human bile has a specific gravity of 1.026 to 1.032 or so, but is somewhat lighter, about 1.010, when drawn directly from the liver in fistuUe. (&) Chemical. —Bile has a neutral or faintly alkaline reaction. It dissolves readilj' in water, but when mixed Avith alcohol gives a precipitate of mucin. The bile acids, mixed with some color- ing matter, can be precipitated by the addition of strong acids. Its chemical composition varies considerably, the i)ercentage of solid matter, in specimens of human bile taken from the blad- der, ranging from 8 or % up to nearly 20,'?. This depends partly on the amount of mucous secretion that is mixed with it, and also, to a great extent, upon the length of time that it stands in 202 MEDICAL CHEMISTRY. the gall bladder, wliieh is constantly absorbing water from the bile contained in it. The projiortion of the principal constitu- ents, according to analyses made by Hoppe-Seyler * and others, seems to be about as follows : Cholesterin, 0.2 to 0.4^ Bile pigments and mucin, 1 to 3% Lecithin, 0.2 to 0.5;^ Bile salts, 6 to lOj? Soaps and fats, 1.5 to 2.5fc Mineral salts, 0.6 to 1% These substances will be discussed later. (c) Physiological. — So far as we can tell, some of the constitu- ents of the bile, the pigments for example, are purely waste mat- ters; others, like the bile salts, are excreted from the liver, but reabsorbed in the intestines; and still others, little understood at present, are of considerable value in assisting the processes of digestion. Functions. — The presence of bile is essential for the proper di- gestion of the fats. It seems to assist in their emulsification and to aid their passage through the intestinal walls. Bile keeps the intestines and their contents moist and smooth, and thereby materially assists the passage of food along the ali- mentary canal. Hence many valuable iDurgatives, calomel for example, owe their effects to an increase in the flow of bile. It a,lso decidedly increases the i)eristaltic action, and is often admin- istered in pills and in enemata for that purpose. Bile is supposed to have some antiseptic action upon the con- tents of the intestine, and it is a fact that in the absence of bile the fseces are unusually offensive and show marked signs of de- composition. Its value in this respect, however, may be due to its alterative and purgative action rather than to any specific effect upon the germs, for bile, outside the body, readily decom- Ijoses and putrefies. CONSTITUENTS OF BILE. CHOLESTERIN.— CaoHuOH. Occurrence. — This substance is found in small quantities in the bile of all animals, where it is probably held in solution by the bile salts. Under certain little understood but more or less dis- * Hoppe-SeykT, " Phys. Chem.," pp. 299 to 301. CHOLESTERIN. 203 eased conditions, it often precipitates from the bile while it stands in the gall bladder, forming, in connection with more or less mucus, what are known as gall stones. The latter vary in size from the head of a pin to lumps the size of a pea or larger, and their passage from the bladder through the gall duet is fre- quently attended with most distressing, and even dangerous, symptoms. Besides this, small quantities of cholesterin occur normally in the red and white blood cells, nerve tissue, brain, spleen, the in- testinal contents, and in the faeces. It occurs also, under patho- logical conditions, in pus, tumors, tubercular deposits, cataracts, and in hydrocele and other pathological fluids. Cholesterin has been occasionally found in some samples of urine. Preparation. — Cholesterin is best prepared from finely pow- dered gall stones, by thoroughly extracting them with boiling al- coh)ut will quite prevent the passage of albumen, or starch, or car- amel. Instead of papers dipped in starch paste or a film of gela- tin, it is more convenient to use eitlier parchment paper (see pp. 7 and 130), when the sticky, tough surface acts as a colloid, or else animal membranes such as the linings of the bladtler, inte.stines, oesophagus, and the like. It does not matter how fine the latter are; if the membrane is intact, and there are no holes in it, crys- talloid substances Avill pass through and the colloids will stay outside. The sepai'ation of substances by this means is called dialysis. Living animal membranes act in the same way as dead ones Of as parchment paper. It is found that tlie rapidity of ditt'usion is increased by many conditions, such as warmth, motion of the liquid and of the dialyzing surface, difference in composition of the two liquids separated l)y the dialyzer, the removal of the crystalloids as fast as they diffuse through, and an increase in the dialyzing surface. But even if all these conditions are pres- ent, as they ai-e, for instance, to a marked extent in the intestines, the thin animal membrane will still act as a barrier to the pas- sage of any but crystalloid substances. It so happens that almost all the ordinary food stuffs, starch, dextrin, the proteids, gelatin, and the like, are distinctly colloid bodies. Hence, when they reach the inte-stine, although sepa- rated from the blood and lymph vessels of the villi by only a very thin nuMiibrane, they cannot enter the system by a simple pro- cess of diffusion, unless altered in molecular composition. Before, however, they reach the end of the absorbing part of the intestines, they have been thoroughly subjected to the action of the various digestive fluids, the saliva, the gastric and pancre- atic juices, and, to a less extent, the intestinal juice and the bile. Under their influence the colloids, like starch and the proteids, are converted into crystalloid substances, maltose, glucose and peptones, which can pass readily through the intestinal wall and enter into the general circulation. It will be noticed that in eacli case the new product belongs to the same class of proximate principles as the original food stuff, and also that there is but little loss of potential energy in the process, the digested food containing but little more oxygen 216 MEDICAL CHEMISTRY. than it did before. "We shall now discuss these digestive fluids more at length. THE SALIVA. This fluid is derived mainly from the salivary glands, but is always mixed with more or less secretion from the mucous glands of the mouth. Properties. — It is a rather viscid, tasteless fluid, slightly turbid, and with a specific gravity ranging from 1.002 to 1.006. It has, in health, a slight alkaline reaction, averaging, according to Chittenden,* 0.08/':^ Na.COa, but in dysjoepsia or where the secre- tion is very scanty it is sometimes 1^ ^ A . . ^v neutral or even acid. :°-fh.''' \ I •<^"-'- ) Composition. — When examined Yy('-- '•' I J •".'■•"-•■V ' / under the microscope, it is seen to V^^ " )\^ ^__^ contain epithelial and other cells /\-.--t^ from the mucous membranes of the ( '-t^''-' J mouth, the so-called salivary corpus- ^„,.--^ cles, ■i.e., round granular cells from Ftg. IO.-Old Epithelial Cells ^j^g galivarv glands, and great varie- FROM THE Hdmau Mouth. (Frey.) ties of bacteria, and sometimes of other organisms. Of the bacteria, the most striking is the one called Leptothrix buccalis, which forms long, branching chains and is sui^posed to take part in the decay of the teeth. It can be best observed in a little tartar from the teeth, spread out on a slide with a drop of water or saliva. Besides these, the saliva always contains more or less d6bris of food, and, in diseased conditions, such as inflammation of the nose or throat, there are often present both pus cells and broken- down epithelia. It contains, in solution, about 0.5,';; of solid matter. Of this, rather less than one-half is mineral, composed, as in the case of the blood and milk, of the chlorides, phosphates, and possibly carbonates of sodium, potassium, calcium, and magnesium. It contains in most cases small quantities of potassic sulpho-cyan- ide, KSCN, a substance not, so far as we can tell, present in. the blood, nor of any special importance, but which can be detected * " studies from the Laboratory of Physiol. C'hem., Yale College," vol. i., 1884-S.'3. THE SALIVA— GASTRIC JUICE. 217 by the red color it produces in a very dilute solution of ferric chloride. Among the organic constituents, we find mucin, which gives it its consistency, traces of proteid bodies, chiefly albumin and globulins, and the ferment jityalin. Ptyalin.— This substance is found in the saliva of man and of several of the higher animals. It can be precipitated from saliva by an excess of alcohol, and, when separated and dried, it forms a white powder very soluble in water. It decomposes readily in an aqueous solution. As before explained (see Lesson III.), it has the property of converting hydrated starch into dextrin and maltose, and finally into dextrose. Its action is much weaker than that of either the diastase of malt or the amylopsin of the pancreatic juice. It works best, according to Chittenden, in neutral solutions, al- though it still acts in solutions containing as much as 0.2 to 0.3% NaaCOa. The addition of more alkali retards and soon destroys it. It is very quickly injured by even faint traces of acids, if they are free. Thus, free hydi'ochlorie acid of a strength of only 0.003;? stops the action, and of 0.005^ kills it. The presence of proteids protects the ferment for a Avhile from the action of the acid by forming acid albumins with the latter. But even in the stomach, where the acid of the gastric juice is weak and the al- buminous material in tli3 food supply often quite large, it is doubtful if the ptj-alin survives more than a few minutes. Uses. —Although saliva contains the ferment in appreciable quantities, it is not believed to have nnich value as a true diges- tive fluid. The saliva, however, is of the utmost importance, not only in keeping the mouth and (esophagus moist and smooth, but also in lubricating the food and putting it into a condition in which it can pass easily and rai)idly into the stomach. GASTRIC JUICE. The food, more or less disintegrated by the teeth, and with some of the starch changed to sugar, passes into the stomach to undergo the second stage of digestion. Preparation. — The gastric juice can be readily obtained, in a fairlv normal condition, not onlv from dogs and similar animals, 318 MEDICAL CHEMISTRY. but also from man, by the aid either of gastric fistulse or of the stomach pump. Properties. — It is a tliin, almost colorless liquid, with a some- what sour taste. Its sj)eciflic gravity varies from 1.001 to about 1.010, and it contains only small amounts (in man, probably from i to 1^) of solid matter. Its reaction is distinctly acid from the presence of free hydro- chloric acid to the extent of from 0.1 to 0.3 or even 0.4^. Some of the organic acids, principally lactic and butyric, are frequently present in the stomach, sometimes in comparatively large amounts. It is probable, however, that these are not secreted in the gastric juice itself, but produced by some fermentative action from the food after it has entered the stomach. Its acidity is also sometimes affected by the presence of acid salts, generally the acid phosphate of soda, NaH...P04. Composition.— Of the solid matter present in the gastric juice, nearly one-half is composed of mineral matter, principally the phosphates and chlorides of the alkaline and earthy metals. The organic matter consists chiefly of the unorganized ferment pepsin and of a little mucin, already described. There is also present, especially in the stomachs of infant mammalia, some of the rennet or milk-curdling ferment, mentioned in Lesson XVIII. Pepsin. — Pepsin can be prepared in a more or less pure form by two or three different methods, such as, for instance, by ex- tracting the mucous membrane of the cardiac end of a pig's stom- ach with glycerin and then precipitating the ferment with strong alcohol. Prepared in this or in other ways it is a grayish- white, amorjihous powder, which is not hygroscopic, and dissolves slowly in water, and more readily in dilute acid. Its solutions can be precipitated by plumbic acetate or by platinic chloride, but not by mercux-ic chloride, concentrated nitric acid, or even by tannin. It does not diffuse through parchment paper or ani- mal membranes. Action. — Pepsin, when mixed with small quantities of hydro- chloric or, to a less extent, of other acids, has the property, under favorable conditions, of breaking down proteids and many albu- minoids into all)umo8es, and finally into peptones. These bodies are products of hydration, containing more oxygen and hydrogen ALBUMOSES— PEPTONES. 219 and less carbon than the original proteids; and they can be formed by the action of the pancreatic ferment trypsin in an alkaline solution, or by hot sulphuric acid, as well as by gastric juice. Both the peptones, and the albumoses from which they are derived, are divided into tw'o distinct classes, known by the i^re- fixes"hemi" and "anti." The hemi-peptones, when subjected for a long period to the action of tryjjsin, are broken down into the compounds leucin, tyrosin, and small quantities of naphthyl- amin. The anti-peptones, on the other hand, resist the action of the pancreatic juice, and cannot be decomposed by it. Albuniosea. — The albumoses, of which some four vai'ieties have been distinguished, are all soluble in dilute sodium chloride solu- tions, and are precijjitated, either wholly or in jDart, by an excess of that salt. They i-esemble the ordinary proteids by giving a violet color with the biuret test, and by being i^recipitated by acetic acid and potassic ferrocyanide. They can be wholly pre- cipitated by saturating their solution with crystals of ammonic sulphate. They are not diffusible. Peptones.— Tlie peptones represent the final product of peptic digestion. They ai-e very hygroscopic, and are exceedingly solu- ble in water. They are precipitated by only a few reagents, tan- nin, alcohol, mercuric iodide dissolved in potassic iodide, and, to some extent, by solutions of either picric, phospho-tungstie, or phospho-molybdie acids. They are not precipitated by ammonic oulphate, and differ from the other albuminous substances by giving a rose-color with the biuret test, and by being readily diffusible. These peptones, although the final products of the action of gastric juice, are probably actually formed to but a small extent in the stomach itself. They are produced in great abundance by the action of the pancreatic juice upon the partially digested food, and represent the form in which the proteids pass through the wall of the intestines. They are found, however, in such minute amounts in the blood of the portal vein that it is believed that, by the action of the cells of the intestinal membrane, they are reconverted into proteids, such as serum albumin, paraglobu- lin, and fibrinogen, during the process of absorption. 220 MEDICAL CHEMISTRY. Influences Modifying the Action of Pepsin. — The hydrolytic action of pepsin depends directly upon the prior conversion of the proteid into acid albumin or syntonin. This is best done by dilute hydrochloric acid, but will also take place in the presence of phosphoric, sulphuric, or oxalic acid. A certain amount of free acid is also necessary for the action of the pepsin itself. When nitric acid is substituted for hydrochloric acid the pepsin works with much less energy, and with acids like acetic, lactic, and butyric its action is either greatly diminished or entirely stopped. Hence, in cases of dyspepsia the presence of a strongly acid gastric juice, due to even large quantities of the valueless or- ganic acids, is not a counter-indication to the giving of small doses of free hydrochloric acid. The action of pepsin is decidedly stimulated by the presence of small quantities of sodium chloride and, to a marked degree, of arsenic. The action is retarded temporarily by the presence of alcohol, but after the latter is absorbed, which occurs very rap- idly, there is an increased flow of very active gastric juice. General Summary. — The main object of the gastric digestion is probably to prepare the food for the pancreatic digestion. The animal food is disintegrated in the stomach, and the myosin and easily digested portions are dissolved to albumose. This sets free the harder fibres and the fat, which latter is melted and floats on the surface. As soon as the food is reduced to a smooth, pulpy consistency, the pylorus relaxes a. little and allows the acid mass, chyme as it is called, to pass on into the small intestines for further digestion. CLINICAL TESTS ON THE GASTRIC JUICE.* iJuring the last few years it has been found of great advan- tage, Avhen treating patients suffering from diseases of the stom- ach, to make more or less thorough analyses of the gastric juice which they are secreting. For this purpose the stomach is first thoroughly washed out with warm water. Some hours afterward a test meal is admin- istered, usually a light breakfast consisting of a roll and a cup of * Dr. Francis P. Kinnicutt : " Modern Methods of Examination iu Diseases of the Stomach," Medical Record, May 24th, 1890. REACTION — TOTAL ACIDITY. 221 hot water, or of tea without milk or sugar, or sometimes a heavier meal of breatl and meat. A certain time after this meal, an hour in the case of the breakfast, and as much as four or five hours where more food has been taken, the stomach contents are all withdrawn by a stomach tube and, after filtering, are submitted to examination. Of the A'arious tests which have at various times been sug- gested, the following are the most important. Tliey include the determination of — (a) Reaction. (b) Total acidity. • (c) Presence of free acids and of acid salts. (d) Presence of free hydrochloric acid. (e) Presence of lactic acid. (/) Presence of syntonin (parapeptone) and peptone. Reaction. — The i-eaction is usually determined by tlie use of litmus paper or of a few drops of an indicator like Orange No. 3. It ought to be acid, and the acidity may be due, as before men- tioned, to the presence of eitlier free hydrochloric acid or of lactic or other organic acids, or of acid salts. Total Acidity. — This is determined, after the metliods illus- trated in Lesson XV., by neutralizing the juice with a standard alkali solution, in the presence of an indicator. The indicator used is generally phenol-phthaleTn. The standard alkali solu- tion, sodic or potassie hydrate, is usually decinormal. i.e., one- tenth as strong as the solutions described on pp. Ill and 144. In other words, 1 c.c. of it is equivalent to 0.00364 gm. of hytlrochloric acid, HCl. We usually make the test on 10 c.c. of the juice, and, as but slight correction is needed for the specific gravity, the percentage of acidity of any sample, calculated to HCl, will be very nearly equal to ten times the above fraction, multiplied by the c.c. of standard alkali solution used. Thus, if G c.c. of the alkali solution were enough to neutralize 10 c.c. of a sample of juice, the acidity would correspond almost to 6 X 10 x 0.00304 or about 0.21:;^ HCl. In practice, 10 c.c. of normal gastric juice usually roiiuire from 4 to Gi c.c. of the standard alkali solution. Presence of Free Acids or of Acid Salts. — To determine whether 222 MEDICAL CHEMISTRY. the acidity is due to the presence of free acids or not, it is only necessary to add to the juice an excess of calcium carbonate, CaCOs, and notice if the acidity has been diuiinished or de- stroyed. As noticed in Lesson XII., the carbonates are decom- posed by free acids, however weak. The CaCOs, however, will not be attacked by the acid salts. This is shown in our experi- ments by the fact that a dilute solution of HCl is quite neutral- ized by an excess of CaCOa, while the solution of acid sodium phosphate, ]S^aH-2P04, formed by the addition of HCl to the hydro-disodic phosphate, is unaffected. In iDractice, this test may be made quantitatively-, by deter- mining the total acidity both before and after the addition of the CaCOa, or qualitatively, by comparative color tests on the acid- ity with litmus paper. Presence of Free Hydrochloric Acid. — This is a very important determination, for the free HCl in the gastric juice is quite as essential as the pepsin itself, and its secretion appears to be not infrequently interfered with in disease. It is i^erfectly possible, although not very convenient for the practising physician, to determine the actual j^ercentage of HCl in the secretion. Usually, however, the qualitative tests are enough for his purposes; and of those, two are particularly inter- esting, namely : Gilnz berg's phloroglucin- vanillin test,* and Eoas' resorcin-sugar test.f Pliloroglucin Test. — This test is in some respects slightly pref- erable to the other, but unfortunately the reagents employed are both expensive and hard to obtain. The solution of phloro- glucin and vanillin (2 gms. phloi'ogluein and 1 gm. vanillin in 30 gms. of absolute alcohol), when warmed with a little very dilute HCl, becomes red, and deposits cherry-red crystals. The test is so delicate that it reacts with less than 1 part of HCl in 15,000 of water. Only a few drojxs of gastric juice are needed for this test. They should be put in a small evaporating-dish with a drop of the reagent, and gently warmed over a low flame. * A. Giinzberfj. .Tahresbericht ii. d. Fortsch. d. Thier. Chemie, "87, p. 842. + Boas. Jaliresbericht, '88. p. 177. For a comparison of these and other IICl tests, see Jahrosberiebt, '01, p. 239. CLINICAL TESTS ON GASTRIC JUICE. 22'i Resorcin and Sugar Test. — This is about as delicate as the phlorogluein test, and, lijie it, is not affected by free organic acids, and is only slightly affected by acid albumins. The reagent (5 gms. resorcin and o gms. sugar dissolved in 100 gms. dilute alco- hol), when added to a few drops of vei*y dilute HCi in a small evaporating-dish and warmed, also gives a red color. Presence of Lactic Acid.— This acid is usually present quite soon after the ingestion of food, but, in normal digestion, disap- pears when the secretion of HCI has reached its maximum. It can be tested for with a very dilute, almost colorless solution of ferric chloride, FeiCU, which turns yellow with even a trace of free lactic acid. It is best to compare this yellow color with the color of some of the same solution without the addition of any gastric juice. Presence of Syntonin, Albumoses, and Peptones. — These are usually simply tested for together Avith the biuret test. In case any importance is being attached to the presence of the peptones proper in the fluid, it is possible to precipitate out both albu- moses and other proteids by saturation with ammonic sulphate, and then the filtrate can be examined for peptones by the biuret test. Significance of these Tests. — For any detailed discussion of the clinical significance of the various constituents of the gastric juice the student is referred not only to Dr. Kinnicutt's paper, but to numerous articles in the various medical journals. We ought, however, toremark that in the diagnosis of at least two diseases these tests are of very considerable value. Thus, in cancer of the stomach, the HCI is almost invariably either totally absent or very greatly diminished. Accordingly, if of no direct positive value, the presence of free HCI in a gastric secretion in at all normal quantities is directly opposed to a diagnosis of gas- tric cancer. On the other hand, in ulcers of the stomach the HCI and the general acidity is usually considerably increased. Hence, the presence of a highly acid juice, attended with previous vomiting of blood and similar synq)toms, may be considered as a pretty strong indication of gastric ulcer. 224 MEDICAL CHEMISTRY. THE PANCREATIC JUICE. General Properties. — It is not very difficult to obtain the pan- creatic juice by means of fistulse on lower animals, but the prop- erties of the juice, thus obtained, are so much modified by the after-effects of the operation that it is hard to tell the exact char- acter of the normal secretion. We know it to be a clear, viscid fluid, without much odor or taste, and with a decidedly alkaline reaction equivalent, on an average, to about i% sodic carbonate. It contains in solution considerable quantities of solid matter (from 2 to 10!?!), most of which is organic matter. It contains serum albumin in sufficient quantities to form a solid mass on heating, and enough alkali albumin to give a heavy precipitate on the addition of acids. The important constituents, besides the alkali, are the various unorganized ferments by means of Avhich it is able to complete the digestion of the different classes of food stuffs. There are supposed to be four of these ferments constantly present, the amylopsin for carbohydrates, trypsin for proteids, steapsin for fats, and a rennet ferment which coagulates milk. Amylopsin. — This ferment, which can be obtained, in a rather impure form, by precipitation with alcohol from a glycerin ex- tract of the pancreas, resembles very closely, both in properties and action, the diastase and ptyalin already mentioned. It acts, however, much more energetically than the ptyalin, and attacks with ease not only hydrated but even raw starch. It produces maltose and dextro-glueose, the latter being foi-iued in somewhat larger proportions than by the other ferments. Trypsin. — This ferment, which has been isolated by Kiihne and others in a comparatively pure state, changes the albumoses, syntonin, and also the undigested but disintegrated proteids and albuminoids present in the chyme into dialyzable peptones. The action of trypsin differs from tliat of pepsin in several important particulars. It works best in an alkaline medium cor- responding to 0.^)% of sodic carbonate, and, while it still acts in a neutral or even faintly acid solution, it is rapidly destroyed in an acid even as weak as the gastric juice. The proteids subjected to it do not swell up and become transparent before dissolving, as STEAPSIN. 225 they do in the gastric juice, but gradually corrode away, chang- ing directly from a solid to a liquid form. The first stage in this process is the formation of alkali allju- min, corresponding to the syntonin in the gastric juice. The alkali albumin is then broken down into albumoses, both heuii- and anti-, just as by the action of pepsin, and these again are further digested into hemi-and anti-peptones. This is done very slowly by pepsin, but trypsin breaks down the albumoses very rapidly, and hence can easily complete the digestion begun in the stomach. The fundamental difference, however, between trypsin and pepsin is that the former can still further break down the hemi- peptones into the nitrogenous but non-proteid organic bodies leucin and tyrosin, and also, although in small quantities only, into naphthylamin. This action of trypsin probably occurs to but a small extent, if at all, in the body, for the pejDtones are so diffusible that they are probably absorbed into the circulation as soon as formed. Trypsin is able to digest both anti-albumin and the albu- minoid mucin, both of which are unaffected by pepsin. On the other hand, unlike pepsin, it will not digest the fibres of ordinary connective tissue until they have first been converted into gela- tin, Steapsin, or Fat Digestion Ferment. — The exact nature of the action of pancreatic juice upon the fats is not understood, nor has the ferment, to whose presence it is due, been thoroughly isolated. According to the best authorities, however, the pan- creatic juice is able to make an extremely perfect and fine emul- sion of fat, and besides this it has the power of converting a small amount of a neutral fat into glycerin and free fatty acid. The fatty acid thus formed is rapidly changed to soap by the alkali present, and hence probably helps to emulsify the rest of the fat. It is generally agreed that the fat is absorbed in the form of miiuite particles, and is not dissolved, like the proteids and car- bohydrates, during the process of digestion. Rennet Ferment.— This ferment is present in the pancreatic juice, and can be extracted from it in company with the trypsin and amylopsin. It acts in much the same manner as the rennet 226 MEDICAL CHEMISTRY. ferment found in the stomach. Its sj)ecial importance, however, is not yet understood. Leucin and Tyrosin.— These bodies have ah-eady been referred to as tlie final products of the tryi^tie digestion of the hemi-deriv- atives of albuminous bodies. They can be produced from both proteids and albuminoids by the action of hot acids and alkalies, and of different kinds of microbes, and are also probably formed by some of the little known processes of metabolism in the body. Thej' have been found, in normal conditions, in the pancreas, spleen, liver, and some other organs of the body; while in dis- eases, especially those that affect the liver, they appear in consid- p-iG. 11.— Crystals of Leucin (Funke). Fig. 13.— Crystals of Tyrosin (Funke). erable quantities all over the body and can be recognized in the urine. They are both readily diffusible. Leucin. CoHuNOa. — Leucin, when pure, crystallizes in the form of thin, white, glistening plates not very unlike the crystals of cholesterin, and also in little clusters of fine needles, radiating from a centre. When impure, it forms little yellow or brownish lumps and nodules, which look not unlike little drops of oil, and show hardly any crystalline structure. It has rather a greasy feeling, and is hard to wet with water, but dissolves readily in hot water and to a slight extent in cold. It is soluble in hot alcohol, and dissolves with ease in acids and alkalies, forming salts with both. Composition. — Leucin belongs to the fatty group of organic compounds. It is really amido-cai^roic acid, i.e., the fatty caproic TYROSIN. 227 acid, HCoHuOj, already mentioned on paf,'e GO, with an aiuido group (NH,.) in the place of one hydrogen. Hence, with bases it acts as an acid, forming (amido-) caproates of the metals and basic radicals, while with acids it forms compound ammonium salts. Tyrosin. CaHiTNOs.— This substance crystallizes in sheaves or bundles of fine, colorless, radiating crystals which sometimes are large enough to show a prismatic form. It dissolves readily in hot water and hot alcohol, but with difficulty in cold water. It also dissolves in both acids and alkalies, and forms salts with them and also with many metals. Some of the latter have been separated and are quite characteristic. Tyrosin differs in composition from leucin in that, besides a fatty acid and an amido group, it also contains an oxy-phenyl group (CoH ,0H), and therefore must be classed with the aromatic compounds. The i^resenee of both leucin and tryosin in the de- composition products of proteids tends to show that in the latter some of the carbon atoms are an*anged as in the benzol ring, and some in chains as in the fatty compounds. Tyrosin i-esponds very reatlily to the Millon's reaction. LABORATORY EXPERIMENTS. GASTRIC, PANCREATIC, AND SALIVARY DIGESTION. I. Tests on Artificial Peptones. ' Prepare the dialyzer by tying a" piece of wet parchment paper over one rim of the glass ring, so as to make a water-tight cup of it. .Suspend this, from the filter stand, in a beaker containing about three inches of water, so that the paper bottom of the dialyzer sets into the water about half an inch. Place the pep- tone solution inside the dialyzer and let it stand quietly until the end of the lesson. Then test the liquid inside the dialyzer for albumoses as follows : («) Boil a little of the solution in a test-tube = no ppt. (&) Add about an inch of dry NaCl to some of the solution in a test-tube = ppt. IG 228 MEDICAL CHEMISTRY. (e) Acidify a little in a test-tube with a drop or two of acetic acid, HC0H3O2, add a few drops of potassic ferrocyanide, KiFeCye, and boil = ppt. {d) Add about an inch of crystals of amnionic sulphate, (NH4)2S04, to some in a test-tube, and heat = ppt. (e) Add to some in a test-tube a few drops of a solution of tannic acid — jDpt. (/) Test some with the biuret test = violet. Test the liquid outside the dialyzer for peptones as follows : (a) With (lSrH4)2S04 crystals = no ppt. (&) With tannic acid = jDpt. (c) With picric acid = faint cloudiness. {d) With biuret test = reddish color. II. Gastric Digestion. — Test the digestive power of the artifi- cial gastric juice as follows: Reaction. — Put a little fibrin in a large test-tube, fill it nearly full of gastric juice, and place the tube, carefully labelled, in the agate cup half full of water. Let the test-tube rest on a piece of wire gauze set into the cup about an inch from the bottom. Place the cup on a sand bath and warm very gently, testing it constantly with a thermometer until it is between 38° and 40° C. Let the mixture of fibrin and gastric juice stand at this tempera- ture for an hour, stirring it every now and then. Notice that the fibrin first swells up and becomes more or less transparent (see Syntonin, Lesson IX.), and finally dissolves, under the action of the pepsin and hydrochloric acid, to albumoses and, in process of time, to peptone. When it is all dissolved, make the following tests on the liquid, in three different test-tubes : For Albumoses. — Add (NH4)2S04 in crystals = ppt. For Albumoses and Peptones. — Add some solution of tannic acid = ppt. For Peptones.— Try carefully the biuret test. If peptones have been formed in any abundance, the color will be reddish or rose-color. III. Clinical Tests on Gastric Juice, — While waiting for the completion of the gasti-ic and pancreatic digestion experiments, make the following tests upon what is left of the artificial gastric juice: TESTS ON GASTRIC JUICE. 229 1st. Reactioti. — Determine the reaction with a piece of litmus paper. 2d. Total Aeidity. — Place in a small beaker exactly 10 c.c. cf the liquid, add a drop or two of i)lienol-phtlialeiii, and run in carefully from the burette the standard alkali solution, stirring the liquid constantly, until the mixture just turns pink. Head off the number of c.c. of alkali solution used, usually from 4 to (JJ. To calculate the percentage of acidity, expressed in terms of free HCl, multiply ten times the number of c.c. used by the factor 0.00304. 3d. Presence of Free Acids and of Acid Salts. — Add to 10 c.c. of the juice about half a teaspoonful of powdered CaCOs. Mix thoroughly, and, after any efTervescence has ceased, filter the mixture into a small beaker, washing the precipitate two or three times on the filter with water from the Avash bottle, and letting the washings drain into the same beaker. Then add to the fil- trate a drop or two of phenol-phthalein, and determine the acid- ity as above, by titrating with decinormal standard alkali solu- tion. Any acidity thus found will be due to acid salts, while the difference between the former determination and this will be due to free acid. To illustrate the action of the CaCOs, make up two solutions: one of free HCl, by adding two or three drops of HCl dil. to some 25 or 30 c.c. of water; and the other of acid sodium phosphate, NaHsPOi, by adding to a little solution of NanHPO, enough HCl dil. to just Hjake it distinctly acid to test paper. To each of these solutions add half a teaspoonful or so of CaCOs, and after the effervescence has all ceased test each with litnnis paper. Notice that the HCl solution is now neutral, while the NaH_PO, solu- tion still remains acid. 4th. Tests for Free HCl— {a) Phloroglucin Ttst.—Vwt in a small evaporating-dish four or five drops of the juice, and to them add one drop of the phloroglucin-vanillin solution. Warm gently over a Ioav flame, and notice the streaks of red which ap- pear along the sides and on the surface of the mixture. (&) Resorcin Test. — Put in a small evaporating-dish four or five droits of the juice, and to them add one or two drops of the 230 MEDICAL CHEMISTRY. resorcin-sugar solution. Warm gently over a low flame and notice the reddish color which results. 5th. Test for Lactic J.cicZ.— Make an exceedingly weak solution of Fe^Cls (one drop of the latter to 25 c.c. or so of water) and place it in two test-tubes. To one add two or three drops of the juice and notice if its color turns more yellow than the color of the Uquid in the other tube. Repeat this test until you have found the right strength of Fe^Clo to employ. IV. Pancreatic Digestion. —Test the pancreatic juice as fol- lows: 1st. Reaction.— Eotice that it is alkaline to test paper. 2d. iVa^COa.— Notice that a little of it, in a test-tube, effer- vesces when a drop of HCl is added. 3d. Action of Trypsin on Fibrin.— Pwt a little fibrin in a large test-tube, fill it nearly full of pancreatic juice, and place the tube, carefully labelled, alongside the tube containing the fibrin in ,;2:astric juice, in the agate cup. Let it stand there, at a tempera- ture between 38° and 40° C, for an hour, stirring occasionally. Notice that the fibrin does not swell up or become transparent, like the other, but gradually wastes away. At the end of an hour or so test the liquid as above, under Gastric Digestion, for albumoses, for albumoses and peptones, and for peptones. 4th. Action of Trypsin and of the Rennet Ferment on Milk. — Fill a large test-tube nearly full of milk and add about half an inch of the juice. Label the test-tube, place it in the cup, and keep it at a temperature between 38° and 40° C. for an hour. Notice that the milk coagulates in a few minutes, but that the coagulum soon redissolves. At the end of the hour test the milk as follows : {a) Taste it; notice the peculiar bitter taste due to peptones. (&) Add a drop or two of HNO3 dil. ; notice that the casein can be no longer coagulated. (c) Try the biuret test carefully; notice that it gives a reddish rather than a violet color, owing to the presence of pep- tones. Make the following tests on the Glycerin Pancreas Extract : Action of Amylopsin. — Make some starch paste, as in Les- LEUCIN AND TYROSIN. 231 sons I. and III., and put some in two small evaporating-dishes. Let them cool till the paste is at about 40' C, and then to the 1st add a few drops of the extract, and to the 2d add a few drops of the extract mixed with two or three drops of HCl dil». Warm both for a few minutes, but not over W C. Then test each for maltose with dilute Fehling's solution, and by the picric-acid test. The first paste will show maltose, but the second will not. V. Salivary Digestion.— 1st. Microscopical Aj^pearance.— Examine a drop of saliva under the microscope. Notice the epi- thelial cells and debris, bacteria, scraps of food, etc. 2d. Potassic 8ulpho-Cyanide.—Vui a little saliva in a small test-tube and add a drop of much diluted Fe.Clc In mo.st in- stances there will be formed a slight reddish color. Compare this with the color formed in the same amount of water, in another test-tube, by the same amount of FejClo. 3d. Reaction.— 'Notice that, excepting in rare eases, it is per- ceptibly alkaline to test papers. 4th. Action of Ptyalin.—Vni some starch paste into two small evaporating-dishes. To the first add a little saliva ; to the second add a little saliva mixed with one drop of HCl dil. Warm both for a few minutes at not over 40" C, and then test each for mal- tose with dilute Fehling's solution. The first will show maltose, but the second will not. VI. Leucin and Tyrosin.— Test a little of the leucin and tyrosin solution as follow.s : Put one or tAvo drops on a glass slide and let them evaporate. Notice the yellow or brownish, round crystals of leucin, and the radiating, needle-shaped crystals of tyrosin. PAET VIII. THE URINE THE URINE. INTRODUCTION. The various foodstuffs, which enter the system in the form of carbohydrates, proteids, albuminoids, and fats, are all utilized, sooner or later, for the production of manifest energy, by a pro- cess of oxidation. Most of the carbon atoms pass out of the body through the lungs in the form of carbon-dioxide. The greater part of the hydrogen is oxidized to water, and is excreted through both lungs and skin, as well as through the kidneys; while the nitrogen, oxidized to urea and its allies, with the mineral salts which enter the body in the food, and the sulphates and phos- phates resulting from the oxidation of the proteids and albu- minoids, are eliminated from the body almost entirely in the urine. These nitrogenous waste products are distinctly injurious to the system, if retained in any quant'ty, and their excretion is the duty of the kidneys. Besides this, however, tlie kidneys have the further duty of excreting most of the abnormal and su- perfluous substances which at any time enter the system, and also, by being able to separate water from the blood when occa- sion calls for it, they regulate the density and hence the quantity of the blood in the body. Structure of the Kidney Tubules.— The urine is derived from the blood in those portions of the kidneys known as the urinif- erous tubules. These are exceedingly minute, slender tubes, leading, by means of larger and larger channels, into the pelvis of the kidney, which communicates Avith the bladder through the ureter. These tubules have a very long, winding course before they finally reach the pelvis, and are lined their whole length with a continuous layer of highly developed epi- thelial cells. The latter vary greatly in size, in shape, and, it is supposed, in functions, according to the part of the tubule in which thev lie. 236 MEDICAL CHEMISTRY. The tubules originate in what are known as Malpi- ghiaii bodies, cup-shaped en- largements into each of which is inserted a little tuft of blood-vessels known as the glomerulus. The blood-ves- sels of the glomerulus are sep- arated from the interior of the tubule only by a delicate layer of flat epithelial cells, thus affording an opportunity for water and tor diffusible mat- ter in the blood to pass through into the tubule. Af- ter the blood has left the glomerulus, it does not di- rectly leave the kidney, but passes in a series of fine blood- vessels round and round the tubules on their way to the pelvis, and thus gives another opportunity for the execretion of urinary ingredients. Formation of the Urine. — The actual process of secre- tion of the urine in the tu- bules is not at present fully understood, for the reason that it undoubtedly does not depend upon diffusion alone. Indeed, it is generally agreed that the cells which cover many portions of the tubule Fia. 13. -Diagram Represehttng the Course op the Uriniferous Tubes, Based on the Ahhangement as Sekn in the Kidney of the Pig. a, Bowman's capsule ; h, convoluted uriniferous tube ; and c, recurrent arm of loop ; d, descending arm ; e, convoluted passages ; /, collecting tubes joining to form one large, open uriniferous canal, (j, which communicates with another canal, h ; i, main trunk open- ing on the papilla (Frey^). THE UEINE. 237 are of the nature of true secreting cells, as in the various other glands of the body, salivary, gastric, mucous, and others ; and also, that among tlieir sj^ecial functions is that of ridding the system of urea and other nitrogenous Avaste products. The urea is prob- ably formed elsewhere in the body, and is simply removed from the blood by the tubule cells, but some of the other nitrogenous bodies may be very possibly elaborated by them as well as excreted. The epithelial covering of the glomeruli, which is extremely thin and delicate, probably acts " more as a dialyzing medium, al- lowing water and some of the diffusible c o m p o u n d s of the blood, especially inorganic con- stituents and, in abnormal con- ditions, glucose or peptones, to pass through. But even here the cells do not act simply like a sheet of parchment paper. They seem to discriminate between the different crystalloids, as for in- stance in not letting the urea c, glomerulus ; rf, undermost portion of capsule without epithelium ; e, neck ; /, through, and also between col- epithelium of the glomemlus ; and !7, loid bodies; for while serum al- that of the internal surface of thecap- . ,. , sule after treatment with nitrate of bumin, in perfectly normal con- gji^^gr (Frey). ditions, never passes from the blood into the urine, egg albumen, if injected into the system, is rapidly excreted by the kidneys, probably through the glomeruli. It is interesting to notice that, while the formation of urine cannot be considered as simply one of diffusion, still the only constituents of the blood which pass under normal conditions into the urine are, like urea and the different salts, organic and inorganic, distinctly crystalloid bodies. When, however, the nutrition of the cells is impaired, by disturbances of the circula- tion which nourishes them or by actual disease, one of the symp- toms noticed is the presence in the urine of albumin, paraglob- ulin, and other non-diffusible substances. Fig. 14.— a GLOMERri>rs from the Rabbit, a, vas afferens ; b, vas efCereiis ; LESSON XXII. GENERAL PROPERTIES OF THE URINE. Quantity of Urine. — The amount of urine passed in twenty- four hours by a healthy individual varies within quite large limits, depending upon the relative amoiiiit of fluid imbibed and of water given off through the lungs or skin. For an adult the average amount is usually estimated at from 1,200 to 1,500 e.c. (40 to 50 fluid oz.). But besides the physiological variations, many diseases have a decided influence upon the quantity of urine excreted. Thus, the quantity of urine is often diminished in disorders of the cir- culation, and in acute, or sometimes in chronic, nephritis or in- flammation of the kidneys. In fevers, also, less urine is usually passed. Its quantity is increased in diabetes, both insipidus and mc-lli- tus, and in some kinds of heart and kidney disorders. The quantity of urine can usually be increased by increasing the amount of fluid imbibed. It can also be increased, in many cases at least, by the use of certain drugs, known as diuretics, such as citrate and other salts of potash, nitrous ether (sweet spirits of nitre) and others. The determination of the exact amount passed in twenty-four hours is often of great importance in certain diseases not only for its own sake, but also because, unless it is known, it is impos- sible to determine the amount of urea excreted from the body. Specific Gravity. — The density of urine, which averages for healthy individuals somewhere between 1.015 and 1.025, varies, in general, inversely with the quantity. Hence, in conditions of perfect health it is quite possible to find it as high as 1.045 and as low as 1.002. In disease, this rule does not always hold good. The urine, for instance, in diabetes nielli tus is not only excreted in great URINE— COLOR— CONSISTENCY. 230 abundance, but is also, i^ most cases, very heavy from the pres- ence of glucose. In certain kinds of nephritis, on the other hand, the urine, which is diminished in quantity, may also be quite light on account of its small percentage of urea. The specific gravity of a sample of urine ought always to be determined, not only as being of value in detecting certain disor- ders, but also as giving some general information about the solid constituents of the urine. The instruments known as urinome- ters, which are used for this purpose, are simply small hydrome- ters, graduated to read specific gravity directly, with a range of from 1.000 to 1.050 or LOGO. It is always well to test the accuracy of a new instrument by placing it in distilled water and noticing if it stands at the 1.000 mark. Color.— This also, as a rule, is dependent upon the degree of concentration of the urine, and varies, under normal circum- stances, from a very faint yellow to a rather deep brown color. The pigments of the urine have not yet been thoroughly isolated, but it is believed that they are derived from the bilirubin and other coloring matters of the bile. The color of the urine is often influenced by disease, indepen- dently of the quantity excreted. Thus, it is lighter, not onlj' in diabetes, as we diould expect from the increased flow, but also in certain kinds of chronic nephritis and in anaemia. It is perceptibly darker in congestion of the kidneys, and also in fevers, where it is claimed that additional coloring matters make their appearance. It is also often colored by the iiresenee of blood which gives it a reddish tinge, deepening often, on stand- ing, to a dark brown, or of bile pigments which give it a yellow or even greenish tinge. The color of urine is also affected by the use of certain drugs. Thus, large doses of salicylic acid will make it green, while car- bolic acid makes it dark green to black, and rhubarli, brown or red. Consistency. — r^ormal urine is always aqueous, but not infje- quently, in disorders of the genito-urinary tract, it is thick and more or less viscid or ropy. This is quite connnon in severe in- flammation of the bladder, and is due either to the excessive pres- ence of mucus, or to the action of alkaline, decomposing urine upon pus. 240 MEDICAL CHEMISTRY. Reaction. — Fresh urine is usually more or less acid fi'om tlie presence, not of free acids, but of acid salts, principally acid sodium phosphate, NaH2P04, and, perhaps, acid salts of uric acid. It is never perfectly neutral, but while it may occasionally be ampho- teric, it is not infrequently perceptibly alkaline owing to the presence of alkaline phosphates and carbonates. This often hap- pens during digestion. After urine has stood for some time at ordinary temperatui-es the urea present is decomposed by certain bacteria, of which the Microccocus ure^e of Colin is the best known, into ammonium carbonate, according to the foi'mula (NHOsCO + 2H2O = (NH4). CO3 Urea. Ammonium Carbonate. This makes the urine decidedly ammoniaeal in both smell and reaction. It also always produces more or less turbidity, not only from the presence of the bacteria themselves, but from the precipitation of earthy phosjjhates, trij^le phosphate, and simi- lar compounds insoluble in alkaline solutions. The reaction of the urine can be readily influenced both by drugs and by diet. Thus the urine may be made alkaline, not only by actual doses of carbonate of soda and other alkalies, but also by simply diminishing the amount of meat taken, and by feeding upon vegetable food, and especially upon fruit. The latter con- tain quite a large amount of the organic salts of soda and potash, citrates, malates, tartrates, and the like, which seem to be oxi- dized in the system to carbonates. Most diseases have but little effect upon the reaction of the urine. In fevers, however, it is generally more acid than is cus- tomary; while the passage of alkaline, ammoniaeal urine indi- cates decomposition of the urine and the presence of microbes in the bladder — a condition usually accompanied with considerable inflammation of that organ. Transparency. — Urine is never perfectly ti'ansparent, and it may, under perfectly normal conditions, be decidedly turbid. Mucus. — There is always present, in every samjjle of urine, more or less mucus from the lining of the bladder and urinary passages. This is usually exceedingly slight, but it can generally URINE — TRANSPARENCY. 241 be noticed, especially aftftr standing a few minutes, as a faint cloudiness in some j^art of the liquid. It is unatfected by heat, alkalies, or even acids, although the latter occasionally increase the turbidity slightly by precipitating the mucin. Phosphates. — If the urine is alkaline, either naturally or from undergoing the ammoniacal fermentation, there is always a deposit of the earthy phosphates, and, in the latter case, of am- monio-magnesio or triple phosphate. These compounds usuallj' settle to the bottom in a short time, and are readily distinguished, 1st, by appearing only in alkaline urine; and 2d, by dissolving when the urine is acidified with acetic acid. Urates. — If, however, the urine is acid and happens to be concentrated, a deposit is very apt to occur, on lowering the tem- perature, coraioosed of urates of sodium, potassium, calcium, and magnesium. These are usually colored yellow or even red, and form the common brick-dust deposits so frequently met with in chilled urine. They are readily recognized, 1st, by only occur- ring in acid urine; 2d by dissolving on warming; and 3d, by dissolving when the urine is made alkaline. IJicrobes.— Although the normal urine is almost always sterile as it leaves the bladder, it is invariably mixed with germs if allowed to stand without special precautions, and hence, unless specially treated, is bound to undergo decomposition. Both mould and yeast plants frequently grow in it, and can be recog- nized readily under the microscope; while the bacteria multi- ply in it with great rapidity, and are so abundant in stale urines that they often make it quite cloudy. These germs can- not be removed by filtering through paper, and can be recognized, even without the aid of the microscope, by not being dissolved by heat, acids, or alkalies, by the liquid not clarifying on stand- ing, and by the odor and reaction of the urine. The presence of bacteria in any abundance, especially if ac- companied by triple phosphates, in the perfectly fresh urine, is often an indication of disease in the bladder. Pus. — Besides this, in inflammations of the genito-urinary tract, the urine is often made more or less turbid by the presence of pus. These pus cells frequently can only be recognized by careful examination under the microscope, but Avhen in great 242 MEDICAL CHEMISTRY. abundance they may appear as a yellowish- white cloud or sedi- ment. They are also not infrequently found in strings and threads, bound together by mucus. On the addition of potassic hydrate, or in the presence of ammonia, the pus cells can be con- verted into alkali albumin, forming a thick, ti*ansparent, ropy deposit. Epithelial Cells and Debris. — These, as well as the pus cells, can only be properly identified under the microscope, and there- fore will be discussed later. Fat Globules. — Fat occasionally occurs in the urine as minute globules contained in epithelial cells, or, very rarely, in casts, in cases of fatty degeneration of the kidneys, and sometimes in other disorders. There is, however, besides this a condition, known as chyluria, in which the urine contains quite large quantities of fat globules mixed with albumin, cholesterin, and other substances. These may give the urine quite a milky af)pearance. The fat globules can be recognized, not only by the microscope, but also by their rising to the surface on standing. This condition is due to the passage of lymph into the urine through channels made, in many cases at least, by the action of parasites. Odor. — The odor of normal urine is perfectly characteristic, although it varies considerably in intensity according to the con- centration. It is usually designated as aromatic, or simply as urinous. After the urine has undergone decomposition, it smells strongly of aumionia, and at the same time usually has a putrid smellfrom the action of the microbes upon the mucus and other organic matter present. This latter odor is occasionally observed in diseases of the bladder and kidneys, while incases of diabetes mellitus the urine now and then has a sweet or fi-uity smell, and, after standing a little, develops a distinct odor from the setting in of alcoholic fermentation. The odor can easily be influenced by certain drugs, such as cubebs, copaiba, oil of sandalwood, turpentine, and others; and also, to a marked degree, by certain vegetable foods, as, for in- stance, by asparagus. URINE— CHEMICAL PROPERTIES. 2i3 GENERAL CHEMICAL PROPERTIES. The urine is the great channel for excreting from the system either foreign or suijerfluous sohd material. Hence, its composi- tion is extremely complex, and varies considerably, not only with the amount and quality of the ingesta, but also with the course of metabolism in the body itself. It usually contains, when passed in quantities of 1,200 to 1,.500 c.c, some 4 to G:?of solid matter, of which rather more than half is organic. This organic matter is chiefly composed of the crystal- lized nitrogenous compounds, urea, uric and hii)puric acids, and their salts, which represent the nitrogenous waste of the system. Besides these, there are small quantities of pigments, and also, it is believed, of unorganized ferments and of non-nitrogenous bodies, Avhicli have not yet been satisfactorily isolated. Special attention will be given in the next lesson to urea and uric acid. The urates, which are always present to some extent, are, as already mentioned, not very soluble in cold acid urine, and can be precipitated, if in excess, by simply coohng the acid urine down to a low point. This test, although very rough and simple, is often made in practice, because an excess of urates is considered to indicate in many cases a predisposition to rheumatism and gout. The inorganic constituents consist, as in the case of blood, milk, and bone, of the chlorides, suli)liates, and phosphates (tf the alkaline and earthy metals, sodium chloride being in consid- erably greater quantities than the rest. Of the inorganic constituents, the sulphates and phosphates are of but slight importance. The chlorides, however, are usu- ally present in normal urine to a very large extent, forming quite a heavy, curdy precipitate with AgNOs. In severe illnesses they usually diminish, and their return in normal amounts, which occurs in the early stages of convalescence, is often watched for and regarded as a favorable symptom. 17 244 MEDICAL CHEMISTRY. LABOEATORY EXPERIMENTS. THE GENERAL PHTSICAL AND CHEMICAL PROPER- TIES OF URINE. The student will be provided, in the following lessons, with a . number of siDecimens of urine, both normal and pathological. The latter will, if possible, include specimens from diseases, such as nephritis, cystitis, gonoi'rhoea, diabetes and the like, which have more or less marked influence on the urine. The student will be expected to examine carefully as many of these samples as possible, making note, in each case, of the dis- ease, and then carefully recording for each the results of his ex- amination, conducted as follows. I. Specific Gravity. — Test this carefully with the urinometer, reading it always at the top of the meniscus, i.e., the little ring of liquid that forms round the stem of the instrument. II. Color. — If the color is normal, note whether it appears light, medium, or dark. If the color varies, describe it as accu- rately as you can. III. Consistency. — Note if it is anything but a thin, aqueous liquid. IV. Reaction. — Note if it is acid or alkaline to test paper. V. Transparency, — Examine carefully and notice if there is more than a faint cloudinesG, due to mucus. If there is, decide whether it is due to (a) il/?fc?f.s'.— This forms in clouds, and is unchanged by acids, alkalies, or heat. (ta) Earthy and Triple Phosp?iates. —Thefie occur only in alkaline urine, and the latter only after decomposition. They dissolve on acidifying. (c) Urates. — These occur only in acid urines; they dissolve on warming and on the addition of alkalies. (d) Bacteria in Large Quantities. — These occur only in de- URINE— CONSTITUENTS. 245 composing urine, wliicli am be recognized by the smell. They make the whole liquid cloudy, and also cause, generally, a pre- cipitation of phosphates. They cannot be filtered out, and are unaffected by heat, acids, and allvalies. Also in pathological urines — (e) Fas. — This, when in great abundance, may form a creamy white deposit or cloud, or else may occur as white strings and threads. (f) Epithelial Cells and Debris. — These, when in abundance, often look much like pus, although often having a red or brown- ish color. They can onlj^ be properly recognized, like most of the other causes of turbidity, by the microscope. (g) Fat Globules. — Very i-arely liresent. They rise to the sur- face on standing and make the urine milky. VI. Odor.— Notice whether it is of the ordinary aromatic type, and whether it is weaker or stronger than usual. Also notice whether it smells putrid, or ammoniacal, or sweet. VII. Urates in Excess. — If the specific gravity of the urine is at all high, 1.025 and over, test whether the urates are in ex- cess by putting some of it in a test tul)e, cooling it rapidly under a stream of cold water, and noticing if a i^reeipitate occurs. VIII. Chlorides.— Test for these Ijy acidifying half a test tube full of urine with HNOs, liltering off any precipitate that may occur, and then adding to the filtrate lialf an inch or so of AgXOs. In normal urines the resulting precipitate of AgCI is quite heavy, either curdy or lumpy. If the mixture only beconies milky, the chlorides are below the average. IX. Other Inorganic Constituents.— Test for these as follows: (a) Sfiljihates.— Add to the urine HCl + BaCl-, = white ppt. (b) Earthy Phosphates.— W^xke the urine alkaline with XHjOH = Avhite or gray ppt. (c) Alka'li lie Phosphates. —Filter off the ppt. from (b), and to the filtrate add some IS'ILCl and tlien some magnesic sulphate MgSOi = white or gray ppt. N. B. — At the end of this lesson set aside in a conical glass some urine stronglv acidified with HCl. LESSON XXIII. UREA AND URIC ACID. These are the most important substances that are found in the urine. They are the end products of the oxidation of the proteids and alburn inoids of the body, and if for any reason their excretion is hindered and they are allowed to accumulate in the system, serious results are liable to occur. Urea is most prominent in the ui-ine of the mammalia, while uric acid and its salts form the chief constituents of the excretions of birds and reptiles. They both occur together, in the human urine, in j)roportions which differ considerably according to con- ditions not yet understood. On an average, however, it is proba,- ble that in health about 87 per cent, and in fevers about 83 per cent, of the nitrogen in the urine is excreted id the form of urea. UREA. (NH2)2CO. Occurrence. — Urea is the principal constituent of the urine of man and of carnivorous animals. It occurs to a considerable extent in the urine of the hei'bivora, and, though far less abundantly, in the excretions of birds, reptiles, and fishes. It is found in small quantities in the blood, milk, and some other fluids of the body. Q,uantity. — Urea is excreted from the body at an average rate, in the case of a well-fed, healthy man, of from 20 to 35 grammes (f to li oz.) in twenty-four hours. This quantity varies very con- siderably, not so much with the amount of exercise, as with the amount of nitrogenous food digested. In perfect health it has been known to range, according to the food supplied, from under 10 gms. to over 109 gms. per twenty-four hours. It is noticed, under pathological conditions, that in fever the excretion of urea may increase very considerably, even when no nitrogenous food has been administered. On the other hand, in FORMATION AND PREPARATION OF UREA. 247 severe diseases of the kittneys, the amount of urea excreted in the urine may fall far below what would be expected from the diet and general condition of the patient. In this connection it is important to remember that the skin may be called upon, by thorough sweating, to assist the kidneys in getting i-id of some of the urea. If the excretion is seriously interfered with for any length of time the condition known as uraemia may set in, and may be attended with very serious consequences. Formation of Urea in the Body. — It is at i^resent believed that the urea is formed not in the kidneys, but elsewhere in the body, very possibly in the livei", and then is carried in the blood to the tubule of the kidney, where it is removed from the system. Va- rious bodies, such as leucin and also kreatin, have been suggested as the intermediate products between the muscle tissue and ui-ea. Preparation. — Urea can be prepared synthetically by heating together potassic cyanate and ammonic sulphate. The amnionic cyanate, thus formed, is converted, during the ojieration, into urea by a rearrangement of the atoms in the molecule. Thus NH4CNO = (XH2)oC0. Urea can also be extracted from urine which has been evapo- rated down to a thick syrup, by adding nitric acid, filtering off the crystals of urea nitrate thus formed, and decomposing them with BaCOs into urea and baric nitrate. Ba(N03)2. The urea can be extracted from the mixture by hot alcohol. Properties, (a) P/i i/sicaL—Vrea, Avhen pure, crystallizes in colorless rectangular prisms, belonging to the rhombic system. Its crystals are anhydrous, and melt at 130 to 132'' C. It has a bitter cooling taste, resembling that of saltpetre. Water and also alcohol readily dissolve it, forming neutral solutions, but it is insoluble in pure ether and chloroform. (b) Chemical. — The chemical structure of urea, or carbamide as it is called in chemistry, will be readily understood on remem- bering that it is an amide of carbonic acid, i.e., that it is carbonic acid Avith two NHn groups in place of two OH groups. Thus^~^\r-0 H2N\p_pj Carbonic Acid. Urea. Urea may also be considered as a compound where two ammo- 248 MEDICAL CHEMISTEY. nias have one hydrogen in each replaced by one bond of CO. For this reason it forms with acids, both organic and inorganic, a series of erystalhne salts, two of which, the nitrate and oxalate, are less soluble, and hence better known than the rest. The nitrate of urea, which can be easily formed by acidifying concentrated urine with HNO3, crystallizes in white, four or six sided, rhombic plates. These usually overlap each other more or less, and while quite soluble in water are comparatively insoluble in dilute nitric acid. The oxalate of urea forms colorless, rhombic crystals with sharply defined faces. It dissolves but slightly in both alcohol and water. Urea also forms a series of compounds with many metallic salts, such as NaCl, NH4CI, the chlorides and nitrates of Hg (ic), Au, Zn, Cu, etc. These substances are usually crystalline, but vary gi'eatly in solubility, the comi:)ound formed with i^alladium chlo- ride being particularly insoluble. The eomjDOund with NaCl is an interesting example of these bodies. It crystallizes in colorless, flat j)lates, which dissolve without difficulty in water. The compound with mercuric nitrate is of importance as the basis of Liebig's well-known method for determining the percent- age of urea, by the use of a standard solution of Hg(]Sr03)2. The end of the reaction is known by observing when the mixture of urine and mercuric salt form a yellow precipitate, on treating a drop of it with alkali. The compound that is usually formed in this reaction has a composition of SlSToHi . Hg(N03)5 . 3HgO. It forms a heavy, white, crj^stalline precipitate, which is soluble in dilute nitric acid and in solutions of NaCl. Quantitative Determ.ination ofTJrea. Importance. — In many, if not most, cases of kidney disease the insufficient excretion of urea is the main danger to be guarded against. Hence it might be sup- posed that the determination of the urea would frequently be of very great imjjortanee. In practice, however, the analysis is not made as often as might be expected, for two reasons. In the first place, the mere determination of the percentage present in a given sample is worthless, unless the quantity of urine passed in twenty-four hours is known also. And, secondly, even when this is done, and the actual (luantity of urea passed in a given DETERMINATION OF UREA. 249 time is known, the figuivi? are of little value unless at the same time we can estimate, with some accuracy, how much urea oiKjht to pass in that same period. In other words, it is not the actual amount but the relative amount of urea that is of interest, and a i)atient might be more liable to an attack of ura'mia while passing oOgms. (an oz.) a day. when in a state of high fever, or when consuming large ([uanti- ties of meat, than another passing only half that amount, when living quietly on a strictly carbohydrate diet. Methods.— (a) Specific Graviti/.— It is often possiljle to make a rough guess at the percentage of urea from the specific gravity of a sam[)le, if we know, also, the quantity of urine passed, and the couq)arative abundance of the chlorides. In an average sample of urine the quantity may be set at 1,400 c.c, the specific gravity at 1,020, and the amount of urea at 21^. The main constit- uent of urine, Ijesides urea, is sodium chloride, and if that is fairly constant a variation in the specific gravity would indicate a corresponding vai'iation in the amount of urea, and a density of 1.015 might indicate from 1 to l^x, and of l.OoO, from 3 to SAj? of urea. In the presence, however, of other disturbing factors, such as albumin or glucose, even this rough guessing becomes impossible. (b) Liebif/s Jlefhod.— This has already been mentioned. The results from it are fairly accurate and not hard to get, but it has been superseded of late years by the more convenient and equally accurate hypobromite method. (c) Jlijpabroin/te Jlet/iod.— This depends upon the fact that when urea is oxidized the hydrogen is converted into HaO and the carbon into COa, but the nitrogen remains unchanged. Hence, if the oxidation is done in a strongly alkaline medium, which will absorb the CO2, the only gas which will be given oflf will be pure nitrogen, each c.c. of which corresponds to 0.00282 gins, of urea. The solution used to oxidize the urea is a strongly alkaline so- lution of bromine. It is usually made by dissolving 100 gins, of NaOH in 3o0 c.c. of water, and adding 25 c.c. of bromine to this solution. The solution does not keep for more than a few days, so it has been suggested to make up the solution of XaOH by 250 MEDICAL CHEMISTRY. itself, and to fill the apparatus witli this each time, adding the proper quantity of bromine (for tlie Doremus apparatus 1 c.c. is enough) witla a pipette just before using. Several varieties of apparatus have been introduced for mak- ing this test. In our experiments we have used the simple appa- ratus devised by Dr. C. A. Doremus,* and also the more elaborate one of Dr. John Marshall, f It will be noticed that the little Doremus apparatus is much simpler, and is more quickly and easily managed, than the other ; while, if it is used carefully, the results obtained by its use are almost identical with those obtained by Dr. Marshall's method. Another great advantage of the former is that no calculation is needed. It requires, however, very careful manipulation. Functions in Nature. — The urea is purely a waste product, which must be gotten rid of from the body as quickly as possible. It is interesting to notice that while the carbon and hydrogen are thoroughly oxidized in the body by conversion into CO2 and H2O, the nitrogen leaves the body in a very slightly oxidized condition, and that hence the body seems to waste, in the form of urea, a considerable amount of potential energy. URIC ACID. CoH4N403. Occurrence. — Uric acid is always present, in small amounts, in the human urine, and in the urine, not only of carnivorous, but generally also of herbivorous, animals. It is produced in quite large quantities by the lov/er animals, and the excretions of birds and of most reptiles are almost entirely composed of uric acid and axinnonium urate. Hence it occurs in large quantities in the deposits of guano found in dry countries. Preparation, — Uric acid can be prepared pure by acidifying an aqueous solution of snake's or bird's excrement. It can also be prepared, although in an impure state, by making urine strongly acid, and letting the uric acid crystallize out. It some- times crystallizes from urine naturally, after standing a little while. Properties.— When loure it is a fine, light, white powder, which under the microscope is seen to consist of colorless, rhombic crys- * Medical Record, March 14th, 1885. t Zeits. f . Physiolog. Chemie., xi., p. 179. URIC ACID — TESTS— FUNCTIONS. 251 tals, see Plate VI. It dissolves very slightly in water, the im- pure varieties being more soluble than the pure crystals. It is insoluble in aleohol and ether, but dissolves in glycerin. Its solutions in the cold do not have an acid reaction. It is readily solul)le in alkaline solutions, foruung salts, urates, which can be precipitated by cold and by acids, but which can be redissolved on warming or by alkalies. It is decomposed by the hypobromite solution just the same as urea, and hence is almost always estimated with the latter, when the urine is ana- lyzed. Tests.— The prettiest test for the presence of uric acid is the formation of a red or purple coloring matter, known as murexide, when the compound is first oxidized with nitric acid, and then evaporated to dryness with the addition of a drojD of dilute am- monia. This test is often of importance in determining the com- position of a piece of calculus. Functions in Nabure.— Uric acid, on oxidation, yields urea and an organic acid, and hence is often spoken of as a product of in- sufDcient oxidation of the nitrogenous matter of the body. It is probable, however, that it is a true end-product of metabolism in the body, only that for some reason it has been formed instead of urea. Indeed, while in the higher animals uric acid, taken into the system, is excreted as urea, ui-ea that is fed to birds is ex- ci-eted as uric acid. The actual amount of uric acid and of its salts excreted from the body depends, so far as we can see, upon the same conditions as that of urea. The relative amounts, however, vary considerably foT reasons as yet unexplained. It is believed that certain dis- eases, rheumatism, and especially gout, are dependent upon the presence of an excess of uric acid in the system, and for this reason the presence of urates in large amounts is often an impor- tant point in diagnosis. 252 MEDICAL CHEMISTRY. LABORATORY EXPERIMENTS. UREA AND URIC ACID. I. Urea, {a) Quantitative Determination.— Te^i at least three samples of urine, quantitatively, for urea by the hypobromite of soda method, as follows •. 1st. Doremiis's Apparatus.— Fill the apparatus full of the hypobromite solution. Then fill the small pipette up to r^\ '4^(s^ Fig. 15.— Doremus's Apparatus. Fig. 16. — Makshall's Apparatus. the mark with urine, place the end of it well under the upright tulje of the apparatus, and force in the urine slowly and carefully. Take care that all the urine enters the hypobromite solution without any air being forced in at the same time, and that all the gas evolved remains in the graduated tube. When the effervescence has ceased, notice where the liquid stands on the scale, and read off the percentage of urea. UREA AND URIC ACID. 253 2(1. Marshall's Apparatus.— Fill the apparatus full of the hy- pobrouiite solution. Then fill the long bent pipette full of urine, and allow, according to the concentration of the urine, 1, 2, or 3 c.c. of urine to flow gently in under the graduated tube. Three c.c. -will be found sufficient even for quite dilute urines. Care must l)e taken in every case to admit the urine so sloAvly that no gas can escape from the apparatus. When the effervescence has ceased, insert the side funnel-tube, and fill it carefully with hypobromite solution until the level of the liquid inside and outside the measuring-tube is the same. Then calculate the percentage of urea by the rule, " The number of c.c. of nitrogen gas corresponding to 1 c.c. of the urine, multiplied by the factor 0.209, will equal the percentage of urea in the liquid."' After these detei-minations have been made and before proceeding with the rest of the lesson, rinse out the appa- ratus, return to the bottle all the unused hypobromite so- lution, and pour the rest down the sink. In case, also, any of the solution has been spilt on the desk, neutral- ize it with a little acid, and then sponge it off. Other- wise the fumes of the bromine will injure the micro- scopes. (b) Qualitative 2V.s-^.— Make the following tests on the sample of concentrated urine. 1st. Nitrate of Urea.— Lay a thread from a towel or handker- chief on a slide; on it put two or three drops of the liquid ; lay on a cover-glass, and under this run a drop of HNO:i cone. Examine under the microscope with a low power, and notice the rapid formation of large, flat, rhombic crystals of nitrate of urea. 2d. Place some of the liquid in two watch-glasses. To the first add the oxalic acid dissolved in a drop or two of water Notice, under the low power of the mi- croscope, the formation of large, rhombic crystals of oxalate of urea. To the second add a couple of di-ops of a concentrated solution of XaCl. "Warm the watch-glass on a water bath 254 MEDICAL CHEMISTRY. till it is nearly dry ; then set it under the low power of the niicroscoije, and notice the formation-of flat crystals of sodium chloride urea. 3d. Mercuric Nitrate Test. — Add a little mercuric nitrate to a little of the liquid in a test-tube, and notice the dense white ppt. that results. Examine a little of this under the microscope. II. Uric Acid. — (a) Preparation. — Boil some snake's excrement with a little water, and filter the hot solution into a small beaker containing one or two drops of HNO3 dil. Notice the rapid separation of white crystals of uric acid. Examine these carefully under the microscope. Also, from the small beaker of acidified urine set aside from the last lesson take a drop containing some of the dark-colored sediment, and examine under the microscope. Let the drop slowly evaporate on the slide, and notice the peculiar forms as- sumed by the uric acid. (&) Tests. — Test the uric acid in both the above solutions as follows ; TJie Ifurexide Test. — Place some of the solution in a watch- glass, evaporate it to dryness, cover the residue with a drop or two of HlS^Oa cone, and then evaporate to dry- ness on a water-bath. Let it cool, and then add a drop of very dilute NH4OH. Notice the red color, due to the formation of " murexide." Plate VI. Fig. 1. Una from Water Sfilutioii, x :S. Fig. 'i. Urea Nitrate, x 75. Fig. 3. Urea Oxalate, x ■; B'lG. 1. Urea Sodium Chloride, x 75. Fig. 5. Uric Acid from .\cid Urine, x ■i-i. Vir, r, Trie Acid from Snake'-iKxcrcmcnt.x 200. . K. r deL LESSON XXIV. ALBUMIN IN THE URINE. Of the various proteids and albuminoids mentioned already, mucin is the only one that regularly occurs, at least in any ap- preciable quantity, in normal urine. Under abnormal condi- tions, however, the urine has been found to contain serum-albu- min, paraglobulin, iibrin, albumose, peptone and egg-albumin. Of these serum-albumin is by far the most important. It occurs in urine, usually mixed with more or less paraglobulin, in very small amounts, hardly ever over 1 or 2/^ by weight, and in most cases may be considered as an indication of some conges- tion or inflammation of the kidneys. This is true even when the amount of albumin passed in this way is exceedingly minute, and hence it is of the greatest importance to be able to recognize even the faintest traces. It must not, however, be forgotten that in some individuals very slight causes, such as a cold or similar indisposition, irregularities in diet or exercise, etc., are sufficient to produce a temjiorary, and in most, cases a harmless, albuminuria. It is also possible to have albumin in the urine derived from other sources than the kidneys, in which case it is of much less significance. It may come, indeed, from any part of the genito- urinary tract. In almost every doubtful case its origin may be determined by the aid of the microscope, for if the albumin comes from the kidney it is usually associated with casts; while if it comes from the bladder, urethra, or other parts, it is usually accompanied with pus, blood, or epithelial cells. Tests for Albumin.— The best tests for albumin are those al- ready specially described inXesson XIX., where they Avere made tipon diluted serum. All of these tests react with paraglobulin as well as with albumin, and the picric-acid tests also I'esponds to albumose or peptone. 256 MEDICAL CHEMISTRY. Of these tests the ring test with nitric acid, often known as Heller's test, will usually be found the most satisfactory. When carefully made it is exceedingly delicate. If, however, the urine is very concentrated, it may happen that a precipitate will be formed of acid urates or of uric acid. This ring differs from the ring produced by albumin, first, by being usually more or less brown in color, and secondly, by forming not at the exact junc- ture of the two liquids, but distinctly above it. The precipitate can only occur when the ui-ine is very concentrated, and is much less liable to occur when the test is made with diluted instead of concentrated nitric acid. It can be obviated by previously diluting the urine with two or three parts of water. A white ring is also formed by nitric acid, if either turpentine or balsam of copaiba are being taken in any quantities. These drugs can readily be detected in the urine by the smell, and the precipitate, which consists of resinous bodies, dissolves readily in alcohol. This test is so consistent in its results that it is often used for a more or less approximate quantitative estimation. Without going into great details, it may be simply stated that a distinct cloud will form in two or three minutes in urine containing less than j^(f of 1^ of albumin. The cloud will form at once with about ji^ of 1;/, although it will be pretty faint, and must be seen against a dark background. Prom that point up to about ifo, the ring Avill be more or less distinctly granular in appearance, and can be seen without a dark background, while above that the albumin settles in flocks and lumps. The picric-acid test is a very good one also, and upon it is based Esbach's method for determining the quantity of albumin present by means of an "albuminometer." This is a tube with a series of fine graduations at the bottom, and with two marks on the side, noting the points to which it is to be filled, first with urine, and then with the test liquid, an aqueous solution contain- ing 10 gnis. picric acid and 30 gms. citric acid to the litre. The urine and the test liquid are carefully mixed together in the tube and allowed to stand for twenty-fcmr hours, when the albumin will be settled to the bottom, in the form of a yellowish-white pi'ecipitate. Its fiuantity can be estimated according to the ALBUMIN IN THE URINE. 357 graduation at which the precipitate stands. The results with this apparatus are only approximate. Peptonuria. — Of late years the presence in urine of peptone, probably mixed with more or less albumose, has been frequently noticed, especially in connection with diseases where large amounts of pus are formed and broken down in the body. Thus it occurs in the later, softening and resolving stages of pneu- monia, in purulent meningitis, pleurisy, phthisis, and in acute articular rheumatism. Peptone is also found in severe scurvy, and, normally, in the urine of women after childbirth. To determine the presence of peptone, a considerable quantity of the urine is usually taken, and freed, first from mucin by treatment with neutral plumbic acetate, and then from any al- bumin that may be present by means of acetic acid and potassie ferrocyanide. The peptone can then be precipitated by a mix- ture of strong acetic acid and phospho-tungstic acid. LABORATORY EXPERIMENTS. ALBUMIN IN URINE. In this lesson there will be provided numerous specimens of urine from patients suffering with different vai'ieties of kidney disease. It is expected that the student will keep careful records of the general properties of these urines {i\ Lesson XXII.), as well as examine them carefully by the following tests. For de- tails of these albumin tests see Lesson XIX. I. Acetic-Acid and Heat Ted.—FiU a test-tube nearly full of urine. If the urine is alkaline, add 2 or 3 drops of acetic acid until it is just acid to test paper. If the urine is acid already, do not add anything. Then boil the top part of the liquid, and ex- amine it carefully against a dark background. If the liquid, where it was heated, looks at all turbid, let it cool a minute or two, and then add a drop or two of UNO, dil. If the turbidity remains or is inerea.=ed = Albumin. II. Ferroeyanide Test. 258 MEDICAL CHEMISTRY. III. mtric-Acid Ring Test. IV. Picric-Acid Test. Make these last tests exactly as described in Lesson XIX. Before each of these four tests, the urines, if not perfectly clear must be filtered. LESSON XXV. GLUCOSE IN URINE. The urine not infrequently contains, both in health and dis- ease, several representatives of the carbohydrate group, as, for instance, lactose in the urine of nursing women, and invert- sugar after rapidly digesting lai'ge quantities of cane sugar. These substances, however, possess little interest for us compared to the presence of dextro-glucose or dextrose. Glycosviria. — Dextrose is often, if not always, present in per- fectly normal urine, although in amounts altogether too small to be detected by the ordinary tests. It is occasionally found in much larger quantities as the result of temporary conditions, sometimes physiological, as, for instance, after taking an excess of readily absorbed carbohydrate food, and, more generally, in the course of certain diseases, such as cholera, meningitis, and liver disease, or as an effect of certain poisons, such as, for instance, carbonic oxide. When, however, it is persistently i^resent in the urine, it is a distinguishing mark of the disease known as diabetes mellitus, a disease characterized at the same time by an increase, often very great indeed, in the amount of urine excreted. The urine from these patients is usually very light in color, on account of the great dilution of the pigments, and at the same time is unusually heavy on account of the presence of the glucose. The percentage of the urea is not as low as might be expected with such a great How of urine, for along with the excessive ex- cretion of carbohydrate matter there is at the same time a con- siderable increase in the total amount of urea excreted. The mere fact of a urine being light in color and at the same time having a specific gravity of over 1.0:25 or l.OoO is a strong indication of the presence of glucose. 18 360 MEDICAL CHEMISTRY. Tests for Glucose in Urine. — (a) Qualitative. — The different tests for glucose have all been carefully described and explained in Lesson II., and the student is referred to that lesson for full details The Moore's test, as already mentioned, is not as satisfactory with urine as with clear solutions of glucose, because the color of the urine tends to conceal the result. The bismuth subnitrate test is not very satisfactory, for it does not always react joromptly, even when glucose is present, while it is liable to react when other reducing compounds, drugs and the like, are present in the ui'ine. It will be remembered that the Nylander's solution, as in Lesson X., reacts slightly with albumin as well as with glucose. The picric-acid and potash test is valuable for practical work, because bj' it we can examine for albumin as well as for glucose in the same test-tube. It mvist not be forgotten, however, that when no glucose is present the color of the mixture is darkened somewhat, not only by the action of the jDotash upon the picric acid, but also by the presence in the urine of small quantities of creatinin and other reducing bodies. The Trommer's and Fehling's tests are in many respects the most satisfactory. Unfortunately, however, many substances which occur not infrequently in both normal and pathological urines are able to reduce cuiDric hydrate, even when no glucose is present. Thus uric acid, creatin, mucin, urobilin, the bile pigments and similar substances, as well as compounds derived from the administration of balsam, copaiba, salicylic acid, gly- cerin and some less common medicines, react like glucose only, in general, with very much less energy. For this reason the phenyl-hydrazin test is sometimes ex- tremely important in cases where the other tests give dubious results. The reaction, if the directions on pages 24 and 25 are followed implicitly, can be obtained with certainty every time. No substance besides glucose will give these particular crystals, and only a carbohydrate will produce crystals at all under such circumstances. The appearance of the crystals is shown in Plate I., at the end of Lesson V. Glycosuric Acid. — It is interesting in this connection to refer FERMENTATION TEST. 361 to a substance, carefully isolated by Dr. John Marshall,* and called by him urette. Every minute or two stop boiling, let the i)pt. (which should be red) settle, and notice if the color has disappeared from the mixture in the flask. If it still shows a bluish tinge, l)oil again, add a few droiJS more of the diluted urine, and examine the color once more. The end of the reaction will be shown not only by the absence of this blue color, but also by the color of the ppt. changing from purple or dark-red to a bright v-ermilion. When the blue color has entirely disappeared, calculate the percentage of glucose in the original urine according to the fol- lowing rule : " The percentage of glucose will be equivalent to 50 divided by the number of c.c. of diluted urine used." 2d. Fermeutation Test.—^iix with a sami^le of diabetic urine, whose percentage of glucose and whose specific gravity j-ou have already carefully determined and noted, a little yeast which has been thoroughly washed upon a filter. Place the mixture in a small beaker and cover it with a plate of glass or another large inverted beaker, to avoid evaporation. At the end of twenty- four hours or later, if the fermentation has not yet ceased, pass the mixture rapidly through a filter and take the specific gravity of the filtered fermented urine. A difference of one degree in the specific gravity of the urine, before and after fermentation, is supposed to correspond to between i and I of 1% of glucose, or to about one grain of glucose to the fluid ounce. See how nearly the percentage obtained by this test agrees with that previously obtained by the Fehling's test. PART IX. MICROSCOPICAL EXAMINA- TION OF THE URINE. THE MICROSCOPICAL EXAMINATION OF URINE. INTRODUCTION. For clinical jjurposes the results obtained by examininf? a sam- ple of urine under the microscope are of even more importance than those obtained by the chemical tests hitherto described. The sediment which is to be submit- ted for examination is usually obtained by letting the urine set- tle for some hours in a conical glass, and then obtaining a few drops from the bottom, either di- rectly, by means of a pipette or glass tube, or after carefully pouring oflf the top liquid. The practice has recently been intro- duced of putting the urine, con- tained in a test-tube or long slen- der flask, into a centrifugal machine, which, on being rapidly ro- tated, swings all the suspended matter to the bottom in a very few minutes. The urine thus concentrated should be spread out in a thin film on a glass slide, no cover-glass being necessary or, indeed, advisable, and carefully examined under first the low power and then the high power of the microscope. The objective used for the latter purpose need rarely be of greater magnifying power than a one-sixth (inch) objective, while a tAvo-thirds objective will do very well for the preliminary examination. It should be remembered, as a general rule, that an object that is being stud- ied under the microscope should, if possible, be kept moist. In the course of the following lessons the student is expected to make himself familiar with the principal forms and varieties Fio. 17.— Centrifugal Separator FOB Urine Sediments.* Can be obtaiued from J. T. Doughertj-, 348 W, S'.Hh St., New York. 268 MEDICAL CHEMISTRY. of urinary deposits. Tlie specimens will be given out to him, as nearly as possible in the order described, by the demonstrator, who will discuss, at the same time, the XJi'incipal features to be noticed. The student is strongly advised to make careful draw- ings of the different crystals and deposits, and to compare them with the illustrations, not only in the text, but also, wherever possible, in other illustrated works upon urine, such as Tyson's "Practical Examination of Urine," Ultzmann and Hoffmann's "Atlas des Harnsedimente," Peyer's "Atlas of Clinical Micro- scopy," and others. LESSON XXYL SEDIMENTS IN ACID URINE. URIC ACID, URATES, CALCIUM OXALATE, ETC. The urine as passed usually has an acid reaction, and continues acid for some hours until the ainmoniacal fermentation has fairly- set in. During this period there may be deposited any of the following compounds : (a) Ui'ic acid. (&) Acid urates of sodium, potassium, ammonium and calcium; (c) Calcium oxalate ; and more rarely — id) Hippuric acid ; (e) Calcium sulphate. Uric Acid.— This occurs, usually as a red sediment readily seen by the naked eye, in urines that are strongly acid. The crystals are generally quite large, and often form little bunches or concre- tions, which appear like grains of red sand or gravel, at the bot- tom or along the sides of the glass containing the urine. Under the microscope they ijresent very varied forms, ranging from the characteristic whetstone shape to long pointed prisms. They are often united together, forming rosettes and other figures which are sometimes quite beautiful (Plates YI. and VII.). The crystals carj be readily recognized by their color, which in the natural urine is always red or yellow, but, if mineral acid lias been added, maj be either brown or purple. The crystals dis- solve readily in alkalies, and can be reprecipitated from this solution, although slowly, by acidifying. They can also be separated by filtering, and tested by the murexide test, as in Lesson XXIII. The presence of uric-acid crystals, after the urine has stood for some time, is not always a matter of much importance. When, 270 MEDICAL CHEMISTRY. however, the urine is so full of ui-ic acid that the crystals separate almost as soon as it is i^assed, there may be danger of their pre- cipitating in tlie bladder, and thus giving rise to irritation of the bladder, or even to the formation of uric-acid calculi. Acid Urates.— These compounds, although always present in urine, rarely form deposits unless the urine is quite concentrated and is chilled. An excess of these salts, as well as of uric acid itself, is quite common in the urine of fever j)atients, and also of patients subject to either gout or rheumatism. Generally, how- ever, the alarming-looking sediments which are so often met with in cold weather when the urine has been chilled have ab- solutely no clinical significance. They are readily recognized by dissolving in alkalies or on the application of heat. The sediment formed by the urates is almost always amorphous or granular. It ranges in color from a yellowish-white to a quite bright red, the so-called brick-dust sediment. It is principally composed of sodium urate, which also very rarely occurs in a crystalline form as radiating colorless masses or as star-shaped groups of colorless prisms. Among other constituents of the amorphous urate sediment may be mentioned the acid urates of potassium and also, it is supposed, of calcium. "When the ammoniacal fermentation has commenced, even though the urine is still acid, it is often possible to detect the brown, spherical masses of urate of ammonium, de- scribed in the next lesson. Calcium Oxalate.— This salt, which has already been studied in Lesson XIV., occurs not infrequently in both normal and pathological urine, and is especially common after a diet of rhubarb, asparagus, and other vegetables. It sometimes sep- arates from the urine while still in the bladder, giving rise not only to irritation and inflammation of that organ, but also to the well-known oxalate of lime or mulberry calculus. The crystals, as they occur in urine, belong to two distinct classes. The commonest and most characteristic form is that of octahedra (Plate III.), with high refracting powers, which are at once recognized, under the microscope, as colorless squares or rectangles with diagonal lines. Besides these, we sometimes find what are known as "hour- Plate V 11. Uric acid crystals. Sediment iu acid urine. HIPPURIC ACID. 271 glass " crystals, oval-shaped bodies, not much unlike a side view of a large colorless red blood-cell. The depression in the sides may be more and more pronounced until it gives rise to the " dumb-bell " form, where the crystal consists of two little spheres united by a larger or smaller band. These crystals are much smaller in size than those of uric acid, and can rarely be recognized without the aid of the one-sixth objective. They often make their appearance soon after the urine is passed; but as they are soluble in strongly acid urine, they are sometimes only precipitated after the al- kaline fermentation has com- menced. They do not dissolve in alkalies, and hence will still be found after the urine has become strongly ammoniacal. Hippuric Acid. — This com- pound is excreted by herbivor- ous animals in large amounts, but it is present in human urine only in small quantities, and hence is but rarely found as a sediment. Occasionally, however, as for instance after taking benzoic acid or after feeding on certain kinds of fruit, crystals of hii^iraric acid are found in the urine. It has no clinical significance. The crystals vary considerably in size. They occur usually as colorless prisms with sharply defined ends, or, more rarely, as colorless needles. They can be distinguished from uric acid, which in other chemical properties they somewhat resemble, by not reacting Avith the murexide test. Calcium Sulphate. — The crystals of this compound have al- ready been examined in Lesson XIV. They occur occasionally in the urine in the form of radiating needles (Plate II.), but are of no particular importance. Fig. 18.— Crystals of Calcium Oxalate. X 350. LESSO]^ XXVII. SEDIMENTS IN ALKALINE URINE. After the urine has stood for some hours at a moderate tem- perature it becomes alkaline, from the formation of ammonium carbonate, and then a new series of dei^osits make their appear- ance. These are all characterized by being soluble in dilute acids and by not dissolving when warmed. They are mostly coiuposed of the amorphous earthy phos- phates, which are regularly precipitated in urine that is alkaline when passed, as well as in urine that has undergone fermenta- tion. Besides these we have, in crystalline form : (a) Triple phosphates. (&) Ammonium urate. (c) Calcium phosphate. (d) Calcium carbonate. There may also occur, usually under iDathological conditions, the rare deposits of leucin, tyrosin, and cystin. Triple Phosphate— MgNHiP04 . CH2O.— This compound has already been studied in Lesson XIV. It occurs regularly as a deposit in fermenting ammoniacal urine, and is only to be con- sidered as abnormal when it is present in the urine as it leaves the bladder. The feathery shaped crystals (Plate III.), which ai-e usually found when testing solutions for the presence of Mg, occur but rarely in urine. Instead of these, we usually And the so-called " coffin-lid " crystals, colorless rectangular prisms with bevelled faces. They range in size from extremely minute crystals up to great transparent masses, which have but little definition, but are still recognized as ti-iple phosphate by their color, the angles which thoy show, and their presence in an ammoniacal medium. Ammonium. Urate.— Mixed with the triple phosphate we almost always find characteristic yellow or brown spheres, gener- CALCIUM PHOSPHATE— LEUCIN AND TYROSIN. 273 ally with spikes and projections adhering to them, which we can recognize as uninioniuni urate. They vary in shape very much, but can always be distinguished Ijy their color, their apjiearance, and their surroundings. For the typical appearance of urine undergoing alkaline fermentation, see Plate YI. Calcium Phosphate— CasCPOOs, or possibly CaHPO^.— This usually forms amorphous deposits, but now and then occurs in the form of colorless, wedge-shaped, prismatic crystals, which vary considerably in size and shape, and often form stars, with the small ends of the wedges pointing toward the centre. They are found not only in alkaline, but also in slightly acid urines which are very nearly neutral. They have no clinical significance. Calcium Carbonate. — This rarely occurs in human urine, and then, usually, in the form of little grains and spheres, which evolve CO2 when treated with a little acetic acid, are of no special importance. In all samples of urine undergoing alkaline fermentation, it is easy to recognize immense quantities of bacteria, as well as, fre- quently, of yeast and mould plants. Leucin and Tyrosin.— These substances, already described in Lesson XXI., occur occasionally in the urine in cases of acute disease of the liver. They are usually accompanied by consider- ableamounts of bile pigments, which can be readily tested for by Gmdlin's reaction. They are usually recognized in urine by the characteristic crystals (see page 220), which, if not present in the natural urine, will generally deposit, if present, when a few drops of the urine are gently evaporated on a slide. The leucin, as before men- tioned, occurs in little yellow or brownish spheres, much like little drops of oil; while the tyrosin forms sheaves and tufts of fine, delicate, colorless needles. Fig. 19.— Crystals of Calcium Phos- phate. X 150. They 274 MEDICAL CHEMISTRY. Cystin. — This substance occurs rarely in the urine, as a result of some unknown changes in metabolism. It is usually found as a whitish deposit, consisting of small, regular, six-sided plates. It also occurs in irregular masses, and not infrequently gives rise in the bladder to cystin cal- culi. Cystin differs from most of the other organic compounds of the body by con- taining large quantities, some 26%, of sulphur. Its composition, as given by Hoppe-Sej'ler, is C3H7lSrS02. It is insoluble in water and in so- lutions of ammonium carbonate, but dissolves in acids and in caustic alkalies. Fig. 20. Crystals op Cystin. (Frey.) Plate VIII. 1. Calcium phosphate. 2. Triple phosphate. Urine undergoing alkaline fermentation. Ammonium urate ; triple phosphate ; bacteria. LESSON XXA^II. CASTS. These bodies, the so-called casts of the uriniferous tubules, are of very great clinical importance, and, when carefully studied, often enable the oliserver not only to diagnose a case of kidney disease, but actually to follow its course, and to keep track of the condition of the kidney itself. For this reason the student is advised to examine these specimens with the utmost care, and to become thoroughly familiar with the api^earance and jiroperties of the different varieties exhibited. Formation. — As already stated, in perfectly normal conditions no albuminous matter imsses from tiie kidney in the urine. When, however, from one cause or another, some of the proteids of the blood are allowed by the epithelial cells of the lining to pass into the tubules, the urine is not only made albuminous, but is liable to contain little plugs of albuminous matter that has been coagulated on the way. This coagulation occurs as the al- buminous matter is passing along the long and tortuous course of the tubules, and the little clots or plugs thus formed stop up the tubule more or less completely, and probably prevent it, for the time being, fi'om delivering any urine. AVhen, hoAvever, the back pressure of the fluid behind the plug reaches a certain point, the little clot of albuminous matter is forced down through the windings and folds of the tubule, and finally is driven out into the urine. These little clots are what we designate as casts, for they may be considered as casts of the parts of the tubule where they have been formed, made out of coagulated proteid matter. General Appearance.— The casts thus formed are minute, cylindrical masses with parallel, though often much curved and twisted, sides. Generally speaking, they have much the shape of a finger. It is important to remember that the material from which a cast is made is soft and tough, and has been rubbed and 19 276 MEDICAL CHEMISTEY. rolled around a good deal. Hence, one end, at least, is almost in- variably rounded off. They need a magnifying power of at least the one-sixth objective for x^roper definition, although they can often be recognized, especially if dark colored, by a much lower power. It is advisable, particularly when looking for " hyaline " casts, to keep the field of the microscope rather dark. Varieties. — The casts, formed as just described, will naturally look like little particles of coagulated proteid; «.e., they will be comparatively colorless and transj)arent, and will show but little signs of any structure. These are called hyaline (glassy) or, when more opaque, waxy easts, and generally possess no further signifi- cance than the presence in the urine of a little albumin. It has even been claimed that some varieties of hyaline easts do not Fig. 21.— Casts, a, Hyaline ; b, waxy ; c, hyaline and granular ; d, hyaline and epithelial ; e, hyaline and blood ; /, lij'aUue and pus. come from the proteids of the blood itself, but are secreted by the epithelial cells. "When, however, the disorder in the kidneys has progressed so far that the lining itself is disintegrating, not only do the casts become more abundant, but the little plugs of albu- minous matter, as they work down through the tubules, pick up parts of the epithelial lining. Hence we may find, adhering to the casts, either more or less granular matter from the disinte- gration of the cells, or even some of the epithelial cells themselves, which have been detached bodily from the walls of the tubules. The latter we usually call epithelial casts, and the former, ac- cording to the structure of the grains, either fine or coarse granu- lar casts. Besides the casts which have as a basis the hyaline or waxy clots of albuminous matter, it is probable that many casts are formed by the filling up of the tubules by the products of inflam- CASTS. 277 mation. Thus Ave have granular casts, both fine and coarse, where the mass is entirely composed of granules ; and these casts, like the hyaline, may have epithelial, blood, or pus cells adhering to them, when they are named (granular) epithelial, blood, and pus casts respectively. Rarely we find fatty casts, where the minute, shiny globules of fat, either free «r in epithelial cells, are imbedded in granular or hyaline casts. When examining these casts under the microscope, it will be noticed that the different varieties all merge into one another, and that in almost every case they must be described as hyaline and granular, or hyaline and epithelial, or granular and pus casts, instead of being described by one name only. Clinical Importance, — It is hardly our place to speak in detail about the relative significance of each of these varieties. In Fig. 23. — Casts, a. Fine granular ; h. cnarsp granular ; r, epithelial ; cl. blood ; e, pus ; /, fatty. general, however, it is usuallj' agreed that the least alarming are the hyaline and, probably, the waxy casts. As the disease in- creases in intensity the granular casts appear in greater abun- dance ; while in the acute stages of inflanunation the easts are found to carry more and more epithelial, blood, and pus cells. The latter indicate a purulent inflammation of the kidneys, and, with the blood casts, are of great importance in diagnosis, as showing that the pus cells and blood found in a sample of urine actually come from the kidneys, and not from some other i^art of the genito-urinary tract. The easts are not nuich heavier than water, and hence settle rather slowly in the urine, as it stands in a conical glass. The usual rule is to add some antiseptic, such as thymol or carbolic acid, to the urine, and to let it settle for at least twelve hours before examining the sediment. The casts can be separated much !nore rapidly and perfectly by centrifugal action. 278 MEDICAL CHEMISTKY. Owing to their great importance, any samjDle of suspected urine sliould always be examined for casts on at least two or three different slides, before concluding that they are absent. It generally saves much time to run over the sample first with an objective of low i^ower, and then to focus carefully with the higher magnifying power on any object which looks suspicious. LESSON XXIX. BLOOD, PUS, AND EPITHELIAL CELLS. Red Blood-Cells.— The red blood-corpuscles have already been studied in Lesson XIX., although the cells of bullock's blood, There examined, are somewhat smaller than those of human blood. It will be remembered that the blood cells are either colorless or very faintly yellow. They have a clear, sharp, round outline Fig. 23.— Human Red Blood-Corpcscles and Two Leucocytes (Sternberg). (Plates IV. and V.), with, when fresh, a depression which appears, according to the focussing, as either a ddrk or light spot in the centre. After they have soaked for some time in urine or in other light liquids, especially if any decomi)osition has set in, they lose much of their sharp outline, and become puckered out of shape, and more or loss granular, in which case they can hardly be distinguished from the pus cells. In the latter case it may bu advisable to test for the presence 2S0 MEDICAL CHEMISTKY. of haemoglobin in the urine by means of either the haemin or the guaiacum tests of Lesson XX. Tlie latter is extremelj- delicate and can be applied to urine in a test-tiibe, without the necessity of staining a piece of paper with it. But unfortunately it reacts with so many other substances— pus, epithelial cells, spermatic fluid, and the like — that it is of value only as a negative, and not as a positive test. It is far better to evaporate a little of the urine to drj-ness in a watch-glass, and to make the htemin test on some of the residue. Blood, if present in the urine, may come from any part of the genito-urinary passages. If it comes from the kidney, in which case it is an extremely grave symptom, it will usually be accom- l^anied with some blood casts. It is normally present in fe- male urine passed at the men- strual period. Pus Cells. — These may be briefly described as broken- down white blood-cells which have been killed while en- gaged in combating some in- flammatory iDrocess. Properties. — They are readily distinguished from blood cells by being distinctly granular in structure, and having a rather irregular outline. They are somewhat larger than the blood-cells, and are quite colorless under the micro- scope. When present in great abundance, they may give the urine a white or creamy appearance. When pus cells are treated with a little acetic acid, they lose their granular appearance and their nuclei become distinctly visible. The addition of potassic hydrate, on the other hand, causes them to dissolve to a gelatinous mass. This also occurs when the pus cells are allowed to stand for a while in alkaline urine. Derivation. — These cells may occur in the urine from inflam- mation of any j^art of the genito-urinary tract. When they come FiG.24.— Pi's Cells, a. Natural condition b, after the addition of acetic acid. PUS CELLS. 281 from the kidney, they indicate a purulent inflammation of that organ, and are usually acconii)anied with pus casts and with considerable amount of albumin. When they come from the bladder, in cystitis, the urine is usually undergoing decomposition and not infrequently is alka- line enough to convert the cells into a slimy mass much like mucus, sometimes before they leave the bladder. In female urine pus cells are frequently present, although visually in but trifling amounts, fi'om slight chronic affections of the vagina and sometimes of the neck of the uterus, as well as in more acute disorders. Urethritis. — In male urine pus very frequently is present from inflammations of the urethra, both acute and chronic, and in both cases it is a very important means of diagnosis. In acute attacks it is of great importance to limit the inflammation to the anterior portion of the urethra ; and as long as this is the case, the urine that is first passed will contain all the pus and other products of inflammation. But when, from one cause or another, the disease has passed the triangular ligament, and reached the posterior part of the urethi'a, some of the pus constantly runs back into the bladder and there mixes with the urine. Hence in all cases of posterior urethritis, as well as of the prostatitis and even cystitis which are then so liable to follow, the last urine that leaves the bladder will still contain some pus cells. For this reason, in all cases of urethritis it is advisable to have the urine that is to be examined passed first into one, and then, after the urethra has been cleansed by the flow of liquid, into a second receptacle. These two samples should then be examined for pus cells. Another very important point, which can best be settled by the examination of the urine for pus cells, is whether a case of urethritis has been thoroughly healed, or whether there Is still some chronic inflammation. In quite a large percentage of cases, even where the attack has been slight and without complications, and has apparently been completely healed, there still remains a little inflammation at some point or another, either behind a stricture, or at some so-called granulating patch, or, very com- monly, just behind the meatus. These spots often remain un- 282 MEDICAL CHEMISTRY. 25. — gonorrhceal threads, with Few Spermatozoa. healed for years, and all that time a patient may be in an infec- tious condition, or may, according to some authorities, be liable to a return of the acute symp- toms. By examining the first urine that is passed, it is always l^ossible, in such cases, to de- tect the so-called gonorrhoeal tln-eads, which are little strings of pus cells with generally some epithelial cells from the ure- thra, or even from the neck of the bladder, tied together with mucus. By careful examination of these threads, cleansed from urine, split open, dried on a slide, and stained with fuchsin, the presence of gonoeocci may often be detected in patients who for years have considered themselves, and have been considered, quite free from infection. Epithelial Cells. — These occur in small quantities in all urines, but are specially abundant in certain diseased or abnormal conditions. They can be described as masses of protoplasm with single nuclei, and, usually, more or less granular in structure. They may come from any part of the genito-urinary tract, and different authors have tried to identify the various cells and state positively their origin. This, however, is rarely possible, even under the most favorable circumstances, and for all practical purposes it is best to divide them simply into round, columnar, and squamous cells. liound Ejjithelial C'eZZ.y.— These are very much like large pus cells, but differ from them by their size, and also by having only a single nucleus. These round cehs are usually supposed to come either from the pelvis of the kidney, or fronx the male urethra. Some of them may come from the bladder, and also, it is claimed, from parts of the uriniferous tubules. In the latter case they are usually associated with albumin and casts. Columnar Cells. — These are of various shapes and sizes, a.nd EPITHELIAL CELLS. 283 generally eonie from small passages like the uretln-a and ureters, and, probably, the tubules of the kidney. It is claimed that some of them may also be derived from the kidney pelvis. Squamous Cells: —These are the large, flat " pavement " epithe- lial cells which cover broad surfaces, and hence are usually de- rived from the vagina or the bladder. The vaginal cells are gen- erally the largest and often come in sheets formed by several cells overlapping one another like the tiles on a roof. The bladder cells are generally smaller and thicker. @ © m © § ® Fig. 26.— Epithelial Cells, rf, Roimcl: ?>, columnar ; r, squamous. All these cells are, usually, somewhat swollen and broken down by the action of the urine itself, especially if alkaline, and of bacteria. Interesting specimens containing these cells from various parts of the vagina and uterus, in all stages of decomposi- tion, mixed with a little blood, can be obtained from women im- mediately after child-birth. As the uterus returns to its natural condition some of the vascular tissue, left behind after the ex- pulsion of the placenta, undergoes fatty degeneration, and forms a discharge known as lochia, which passes off in the urine. In normal cases this din)inishes quite rapidly, and finally ceases in the course of four or five days. LESSON XXX. SPERMATOZOA, MICROBES, FOREIGN BODIES. Spermatozoa. — These are found not infrequently in the urine both in healtli and in disease. They are exceedingly minute bodies with a head shaped some- thing like a pear or an acorn, and with a long, slender, tajpering tail. They cannot be seen with anything but a high-power objective. Microbes. — These have alreadj^ been quite carefully discussed in Lesson IV. In decom- posing urine we frequently find examples of all three classes, the moulds, yeast plants, and bacteria, illustrations of which have been given in Plate 1. The mould plants are the least common, and occur usually after the urine has been standing for some time, excepting when giu cose is present, when they appear in large quantities just after the alcoholic fermentation. The mycelium is the only part of the plant that develops in urine, and it is easily recognized by being in the form of slender strings, of greater or less length, composed of colorless, oval cells placed end to end. The yeast fungi are i^resent in small quantities in almost all decomposing urines, although they develop rapidly and in great abundance only in urines containing glucose. They consist of round or oval-shaped, nucleated, colorless cells, to whose sides some buds or small cells are usually attached. The bacteria are invariably present in abundance, and can be easily recognized, with a high-power objective, in all decomposing urines. The micrococcus ureae is perhaps the most important of the bacteria that are connected with the ammoniacal fermentar tion, but with it are associated bactej-ia of every size and shai^e. Fig. 27. — Human Spermatozoa, Very Highly Magnifed. (Frey.) FOREIGN BODIES. 285 These germs are in most cases non-pathogenic, and hence are not indicative of any disease, unless, as in cystitis, for in- stance, they cause the urine to decompose inside the body. It is, however, claimed by a large number of excellent authorities that ordinary bacteria, or even specific disease-germs, have fre- quently been met with in the fresh urine in certain diseases. Thus they have been found in acute nephritis, ulcerative endo- carditis, erysipelas, and also in pneumonia, typhoid fever, glanders, and especially tuberculosis. In the latter case the bacilli may be detected by drying and staining, just as in sputa, and their presence may sometimes indicate the true nature of a kidney disease, occurring in tuberculous patients. ■Foreign Bodies.— As a rule the power of at once distinguishing foreign bodies, such as particles of dirt or dust, air bubljles, threads, fibres, pieces of clothing, etc., which constantly occur in urine, can only be acquired by practice. There are, however, a few i^oints about some of them Avliich it may be well for the stutlent to remember. Air Bubbles: — When air bubljles are of large size, it is impossible to mistake them for anything else; but when very small, thej are often mis- taken by the inexj^erienced student for fat-globules and even for red blood-cells. When by themselves they are circu- lar in shape and can always be distinguished by thi^r very sharp, distinct, strongly refracting outlines, and by the total absence of any structure. Threads and Fibres. — These are often found in samples cf urine, derived either from clothing, or from towels and washing- cloths, or from the dust of carpeted rooms. They are not infre- quently mistaken for casts, but can readily be distinguished, not only by their general appearance, but also, Avith great ease, by examining their ends. The east is formed of a soft material, and Fig. 28.— Fibres, n, "Wool ; ft, cotton c, liuen. X 25. 286 MEDICAL CHEMISTRY. hence one or both of its extremities are always more or less rounded and smoothed off. But fibres always have either square ends or ends that are broken and jagged. The commonest fibres met with in urine are of wool, cotton, or linen. The wool fibres are of animal origin, and are composed of cells whose edges, as seen in the figure, give the fibre a somewhat serrated structure, and thus, by the way, give it its felting prop» erties. The cotton and linen fibres, on the other hand, consist of cellulose, and present no special structure. It will be noticed that the cotton threads have a curious twisted appearance which the others lack. APPENDIX A. TABLE OF WEIGHTS AND MEASURES. ENGLISH WEIGHTS. Pound. 1 Ounces. .. 12 1 TROY WEIGHT. Pennyweights. 240 20 1 Grains. . 5,700 . 480 24 French Grammes. 373.2419 = 31.1035 = 1..5552 APOTHECARIES' WEIGHT. lb. Pound. 1 5 Ounces. .. 12.... 3 Drachm.'i. .... 90.... .... « .. 1.... Scruples. ... 288... ... 24 ... 3.... 1.... Grains. .. 5,7Gu . . 480 GO 20 1 French Grammes. 373.2419 31.1035 3.8879 1.2f).59 = 0.0G48 AVOIRDUPOIS WEIGHT. Pound. 1 0^lnces. ... 16... 1... Drachms. ... 2-,G ... 16 1 Grains. French Grammes. . 7,000 = 453.5920 . 4:37.5 = 28..3495 27.343= 1.7718 METRIC MEASURES MEASURES OF LENGTH. 1 Millimetre = 0.001 of a metre. 1 Ceutiinetre — 0.010 of a metre. 1 Decimetre = 0.100 of a metre 1 j>I«tre = 1.000 metre 1 Deciimetre = lO.ono nietres. 1 lUvtometre - lUD.dilO metres. 1 Kilometre = l.rtio.ooi) metres 1 Myriametre - 10.000.000 metres about 4 inches. 39.37 inches. about % of a mile about (5 1-5 miles. 1 Centiare 1 Are 1 Hectare MEASURES OF SURFACE. 1 Square metre 100 S 1 Quart, wine measure = 33 fluid ounces 0.9463 litre. 1 " imperial = 40 fluid ounces 1.1.358 litres. 1 Ton avoirdupois (2,000 lbs.) 29,166% oz. Troy. 1 TDiiiieau = 1,000,000 gms 1,000 kilos. Reprinted, by permission, from Prof. J. II. Appleton's " Laboratory Handbook," Providence, R. I. APPENDIX. 289 APPENDIX C. TABLE OF ATOMIC WEIGHTS. (Issued December Gth, 1890.) Revised for the Committee of Revision and Publication of the Pharmacopoeia of the United States of America. BY F. AV. CLARKE, Cliief Chemist of the United States Geological Survey. This table represents the latest and most trustworthy results, reduced to a uni- form basis of comparison, with Oxygen = 16 as starting-point of the system. No decimal places representing large uncertainties are used. When values varj', with equal probability on both sides, the mean value is given in the table. Name. Aluminium . . Antimony... . Arsenic Barium Bismuth Boron Bromine Cadmium Caesium . . . Calciiun Carbon Cerium Chlorine Chromium . . . Cobalt Columbimn'. Copper Didymium". . Krbium Fluorine Gallium ... . Germanium.. Gluciuum^. . . Gold Hydrogen Indiimi Iodine Iridium Iron Lanthanum.. Lead Lithium Magnesium.. Manganese . . Mercury Symbol. Atomic Weight. Al Sb As Ba Bi B Br Cd Cs Ca f! Ce CI Cr Co Cb Cu Di Er F Ga Ge (il Au H In I Ir Fe La Pb Li Mg 3In Hg 27. 120. 7.5. 137. 208.9 11. 79.93 112. 132.9 40. 12. 1J0.2 .35.43 52.1 59. 94. 03.4 142.3 160.3 19. 69. 72.3 9. 197.3 1.007 113.7 126.85 193.1 50. i;}8.2 206.95 7.02 24.3 55. 2(;k). Name. Symbol. Atomic Weight. 3Iolybdenum Nickel Nitrogen Osmium O.xygen* Palladium Phosphorus Platinum Potassium . . Rhodium . Rubidium . . Ruthenium . Samarium. . Scandium . . Selenium. . . Silicon Silver Sodium Strontium. . . Sulphur Tantalum . . Tellurium . . Terbium Thallium Thorium . . . Tin Titanium Tungsten Uranium Vanadium. . Ytterbium. . Yttrium Zinc 2^rcoiiium. . Mo Ni N Os () Pd P Pt K Rh Rb Ru Sm Sc Se Si Ag Na Sr S Ta Te Tb Tl Th Sn Ti AV U V Yb Yt Zn Zr 96. 58.7 14.03 191.7 16. 106.6 31. 193. 39.11 103.3 K5.3 101.6 1.50. 44. 79. 28.4 107.92 23.05 87.6 32.00 182.6 125. 1.59.5 204.18 232.6 119. 48. 1S4. 239.6 51.4 173. 89.1 65.3 9H H 1— 1 IS W H e W u fi fi ^ ;25 3 < X! <^ C/J 1— 1 P so n a '5 q o H O CM o c < r "5 O 3! R -3 ^ o 1 ti S fl igi -^ C M O'^ ^tt =*-^ S-H ^l^i^ 2^ ail Ei^ S 2.2t4^^5?^|2 tsB b g _ s^ _ s -i-('??CCi'-t APPENDIX. 291 ooo"| 500 c-i o .■ ■" t> o CS c.D'-" a;K5.S.! i2^ 5 .ii -- C « ; . • =* > i. ,- 5 X s 3 ; - t- X cj o -- ?j ! :t-x 05O — ■?» ■^^^Z^Zf.'^.'i^ KK rt •*■ Ti ^ rt cS — ^. Cti P^ i/ IJ 2h O ^ C-i ^ « ►-sxccicCJa) o fs c: 5^. S'. k'n 55 tai fe o 'e ^ 2 rS|. ga o 5>D o o o 5j ^ t 1--= 20 §1 . aJ ••? '-' '7 ■" T '-^ ^- a l^^,llllll lljlill sslj^optH AiS-;;:, (!.«<; 8 to (U, (J.5 of Milk, 177 to im of Oils, 63, 04 Albumin in Urine. 2.5,5 Peptonuria, 2.57 Tests, 193, 2.55 Acetic Acid and Heat, \m, 19.5.2.57 Ferrocyanide. 193, 195 Nitric-Acid Ring, Heller's, 193, 196, 256 Picric- Acid, 194, 196, 2.56 Albuminoids, 73. 76, 166, 167, 170 Albumins, 72, 76 Egg Albumen, 76, .SI, 82 Serum Albumin, 78,81, 82, 102 to 197, 255 to 259 Tests, 81, 82, 196, 2.57 Acetic-Acid and He;it, 193. 19.5, 2.57 Ferrocyanide, 193, 195 . Nitric-Acid Ring, Heller's, 193, 196, 256 Picric- Acid. 194, 196, 2.5G Albuminate; see Alkali Albumins, 87 to 80 Albuminoid Ammonia. 1.52, 156 Albumoses, 72, 219, 223 Biuret Test, 75, 81 Tests, 227, 228, 330 Alcohol, Ethyl Alcohol, 43 to 48, 1S:^, ISO Preparation. 40, 42, 183 Tests, 46, 48 Acetic- Ether, 40, 47 .Mcohol. Tests, Chromic-Acid, 45,47 Iodoform, 45, 46 ; Plate 1., Fig. .? Molybdic-Acid. 47 Alcoholic- Fermentation Test for Glu- cose, 261 to 264 Alkali Albumins (Albuminates), 87 to 89, 234, 225 Alkalimetry; see Aeidimetry, 141, 114 .\lkaline Metals, 138 U) 144 Ammoniimi, 138, 142, 272, 273; also see Ammonia Lithium, 140, 14;^, 1.58, 161 Potassium, 140, 343 Sodiun-., i:W. 143 Aluminium, 127 Tests, 131, 132 Alums, 128. 129, 131 ; Plate n.,Figs. 3 and 4 Anmionia, 138, 151 to 155, 159, 167, 169 Albuminoid, 1.52, 156 Free, 151, 152, 150, 1.59 Ammoniacal Decomposition of Urea, 240; also 272, 281, 284 Ammonium, 138, 142 ; Plale III., Fig. 6; see also Ammonia Ammonium Urate, 272 Amyloid Substance, Lartlacein, 72, 01, 93 Amylopsin, 31, 224. 230 Aniline Test for Nitric Acid, 119, 123 Animal Proteids, classification, 72 ; sttt also Albumins, Fibrin. (Jlobulins, etc. Arsenic, Marsh's Test for, 10.5, 111 Ashes of Body, 109, 170 of Bone, 108, 109. 170 of Wood, 141, 143, 144 Bacteria. 34; Plate I., Fig. 6 in Saliva, 216, 231 in Urine, 284 Bile. 201 to 207 Tests, 205, 207. 209. 210 Bile Acids, 201, 206, 207, 210 Bile Pigments, 201, 202, 204, 205, 309, S1(J Bile Salts, 201, 202, 206, 207, 210 Bdirubin, Biliverdiu; see Bile Piguietit-s 310 INDEX. Bismuth-Subnitrate Test fcr Glucose, 20, 25, 96, 98, 200, 262 Bismuth Test for Sulphur, 96, 98 Biuret Reaction or Test, 75, 81 for Albuminoids, 170, 171 for Peptones, 819, 223, S28, 230 for Proteids, 81, 83, 88, 89, 97, 18G, 196, 196, 228 Blood, 187 to 201, 20S, 279 Color, 188, 195 Compopicion. 189, 190 Corpuscles or Cells, 187, 189, 198 to 200, 279. 280; Plates VI. and VII. Experiments on, 194 to 197, 208, 209 General Properties, 187 to 190 Hasmin, 192 Haemoglobin, 190, 191, 194 in Urine, 279, 280; Fig. 29, ;\ 279 Quantity, 188 Reaction, 188 Specific Gravity, 188 Blood Stains, Detection of, 197 to 202, 208, 209 Examination of Blood-Corpuscles, 198, 208 Spectrum Analysis, 200 Tests Guaiacum, 197, 208 HEemin, 300, 209 Bodies acting like Ferments, 29 Bone, 165 to 172 Composition, 165 to 166 Tests on, 169 to 172 Bone Ashes, 168, 169 Bone Black, Bone Charcoal, 167, 169 Breast Milk Clinical Tests on, 181, 182, 185 Composition of, 173, 174 Brucine Test for Nitric Acid, 119, 123 Butter, 59 to 62, 65, 173, 174, 177. 181, 182, 184, 18.5, 186; Figs. 5 and 6, pp. 172 and 173 Adulteration.s, .59, 60, 65 Composition, 60 Occurrence, 59, 17.3, 174, 177, 181, 182 Oleomargarin, .59, 65 Preparation. .59 Tests, 65, 185, IKC, Caloiitm, 133 to 137. 147 to 149, 1.58, 168, 170 Carbonate, 47, 116, 121, 1:M, 136, 273 ; Plate II., Fig. 5 Oxalate, 1.34, 136, 270,271 ; Fig. IK, p. 271 ; Plate III., Fig. 1 Phosphate, 273 ; Fig. 19, p. 273 Sulphate, 115,121, i:J4, 137, 271 ; Plate U., Fig. 6 , Calcium Tests, 134, 136, 137, 147 to 149 ; also 47, 144, 158, 161, 168, 170, 197, 243, 245 Cane Sugar, Sucrose, 36 to 38, 41 Carbohydrates, 3 to 5 Classification, 4 Composition, General Properties, etc., 3; also see Cane Sugar, Cellu- lose, Glucose, Lactose, Starch, etc. Carbonate; see Calcium Carbonate Carbon Dioxide ; see Carbonic Acid Carbonic Acid, 116 to 119, 121 in Fermentation, 44, 47, 183, 186, 261 Tests, 121; also 47,143, 160, 169, 230, 273 Casein, 72, 175, 184 Castor Oil, 02, 66 Casts (of the Urinif erous Tubules), 275 to 277 Cellulose, 6 to 8, 11, 12, 286 ; Fig. 28, p. 285 Cliloride of Sodium ; see Chlorides ; also 143; Plate III., Fig. 4 Chlorides in Blood, 197, 208 in Bone, 168, 170 in Milk, 177, 185 in Urine, 243, 245 in Water, 1.54, 155, 156, 1.57, 1.58, 160 in Wood, 143 Quantitative Determination of, 154, 155, 100 Tests, 107, 109, 112, 154, 1.55, 158 ; also 143, 158, 160, 170, 185, 208, 245 Chlorine, 106 to 108, 112 Cholesterin, 202, 203, 209 ; also 80, 84, 165, 173 ; Fig. 9, p. 207 Chromic- Acid Test for Alcohol, 45, 47 Chyluria, 242 Coagulated Proteids, 72, 91, 97 Coagulating Ferments, 81, 32, 84, 85, 86, 90, 175, 184 Coagulation of Blood, 86, 90 of Milk, .32, 175, 184 Cod-liver Oil, 64, 66 Collagen, Ossein, 73, 166, 170 Colloids and Crystalloids, 9, 214, 215 Conversion of Starch into Dextrin, etc., 9. 27, 28, 31, 34, 35, 217, 224, 231 Cow's Milk, 173, 184 ; see Milk Crystallin (Globulin). 84, 88 ( M-ystalloid.s, 9,214, 215 Cystin, 274 ; Fig. 20, p. 274 Dekivki) Albumin.s, 72, 87, 89 ; see al.so Acid Albumins, Alkali Albumins, Syn- tonin Dextrins, General Properties, etc., 13, 14 Preparation, 27, 28, 34, 35, 217 Tests, 24 INDEX. 311 Dextro-Glucose, Dextrose, 10 to -'(i ; also* see Glucose. Dialysis, 214, 215 Diffusion of Fluids, 213 Digestion, 213 to 227 Fernieuts, 28, 30 to 33, 217, 218 to 221, 224, 225 Gastric, 32, 217 to 224, 227 to 230 Pancreatic, 9, 28, 31, 32, 224 to 22S, 230, 231 Salivary, 9, 28, 31, :«, 216. 217, 231 Disaccharids or Saccharoses, 4, 30 to 40 : see also Caue Sugar, Lactose, Maltose, Sugar Dorenius' Apparatus f(jr Urea, 249, 2:)2; Fig. 15, p. 2r)2 Drinking-Water, 149 to l.W. l.^g, lOO Analysis of Croton Water, V^i) Biological Tests, 149, 150 Chemical Tests, 151 to 1.58. 159, 109 Diseases from Pollutioii, 149 Egg Albumen, 70 to 78, 81, 82 Elastin, 73 Emulsion, 56, 58, CO Epithelial Casts, 270, 277 ; Figs. 21 and 22, pp. 270, 277 Epithelial Cells in Jlouth, 216 ; Fig. 10, p. 216 in Urine, 282, 2*3 ; Fig. 26, p. 2S3 Fats, 51 to 54, 50 to 58, .59 to 60 Butter, 59 to 01, 173, 177, 181, 182, IRt Composition, General Properties, etc., 51 to .54 Emulsion, .50, .58. 00 in Blood, 194, 196 in Bone, 165 Oils, 62, 0.5, 06 Oleomargai'iu. 52, 59, 65 Preparation, 51, 52, 56, 58, .59 Fehling's Test for Glucose, 21, 22, 25. 20. 201, 253 Fermentation and Ferments. 29 to 34 ; also 15, 84, 85, SO, 90, 175, 18:3, 217, 220, 224 to 227, 240 Fermentation Experiment, 40, 42 Fermentation Test for Glucose, 201, 262 Ferments, Organized, 33, :J4 ; also see Bacteria, Moulds, Yeast; Plate I., Figs. 4, 5 and 6 Unorganized, 30 to 33 ; also see Di- gestion Fefrocyanide Test for Proteids, 75, 81, 193, 195, 196, 2.57 Ferrous-Sulphate Test for Nitric Acid, 119, 122 Fibrin, 72, 90 E.xperiments, 195 Fibrinogen, 85, 86 Foreign Bodies in Urine, 2S.5, 280 Galactose, 18 (ia.stric Juice, 217 to 224, 228 to ZV) Clinical Tests on. 220 to 224, 229, 2:W Experiments, 228 to 230 Ferments in, 32, 71, 218 to 221, 228 Gelatin, 73, 100, 170 Globulins, 72, 79, 80, 82, 84 to 86, 88 : also see Crystallin, Fibrinogen, Myosin, Paraglobulin. etc. Glucose; see also Dextro-Gluco.se, Galac- tose, Lsevulose. Classification, 4 General Properties, etc., 10 to 19 in Urine, 259 to 204 Quantitative Determination of, 22, 23, 20, 261, 262, 263 Tests Bismuth Subnitrate, 20, 25, 96, 98. 200, 202 Fehling's, 21 to 24, 25, 20, 200 to 204 Fermentation, 261, 202 Moore's, 19, 24, 2(i0, 202 Nylander's, 20, 25, 96, 98, 2ti0. 262 Phenyl-Hydrazin, 19, 20. 24, 260 ; Plate I., Figs. 1 and 2 Picric-Acid, 21, 25, 200 Polariscope. 23 Trommer's. 21, 25, 2t)0 (jlucoside Decomposing Ferments, 31 Gluten Proteids, 73, 94, 95, 98 Glycerin, 61, 62, 66; also 44, 54, 198 Glycogen, 14 to 17, 210 Glycosuria Acid, 200, 261 (Jmelin's Test for Bile Pigments, 205, 209 Guaiacum Test for Blood, 2(10, 209 H^MATIN. 192 Ilsemin, 192 Ha;min Test for Blood, 197, 208 ; Fig. 8, p. 208 Hffinioglobin, 190, 191, 194 ; also 200, 205 Heller's Test for Albumin, 193, 196, 2.56 Ilippurio Acid, 271 Human Milk Clinical Tests in, 181, 182, 185 Composition of. 173, 174 Hydrochloric Acid, 32. 87, 97, 108 to 110, 112, 218, 221 to 223, 229, 230 Clinical Tests for, 221 to 223, 2S9, 230 General Properties, etc., 108 to 110 112 312 INDEX. Hydi'ocliloric Acid in Gastric Juice, &i, 110, 218, 231 to 223, 2,39, 230 Tests, 109, 112 Hydrogen, 104 to 106, 111 Inorganic Constituents of Blood, 197, 208 of Bodj% 169, 170 of Bone (Bone Ashes), 103 to 171 of Milk, 176, 185 of Urine, 243, 245 of Wood (Wood Ashes), 141, 143 Inverting Ferments, 31, 37, 183 Iodine Test for Bile, 205, 210 Iodoform Tests for Alcohol, 45, 40, 186 Iron, 125, 120, 130 in Blood, 169, 170, 191, 197, 208 iu Eggs, 83 in Wood Ashes, 144 Keratin, 73 Koumyss, 183, 184, 186 ; also 18, 39 Lab or Rennet Ferment, 31, 32, 225, 230 Lactose; see Milk Sugar Lsevulose, 18, 37, 38 Lead Test for Sulphur, 95, 98 Lecithin, 204 ; also 80, 177, 190, 202 Leucin and Tyrosin, 226, 231; also 7J, 273; Figs. 11 and 12, p. 226 Liebig's Test for Urea, 848, 854 Lithium General Properties and Tests, 140, 143 in Mineral Water, 158, 161 Magnesium General Properties and Tests, 135, 137 ; Plate III., Figs. 2 and 3 in Bone, 168, 1('0 in Water, 147, 148, 161 in Urine, 272; Plate VIII., Figs. A and B Maltose or Malt Sugar Fermentation of, 40, 41, 42, 44 General Proi^erties and Tests, 35, -10 in Digestion, 217, 224 Preparation, 28, 34, 35 Marshair.s Apparatus for Urea, 249, 253 ; Fig. 16, p. 2.52 Marsh \s Test for Arsenic, 105, 111 Mercuric-Niti-ate Test for Urea, 248, 254 Methaemoglobin, 192 Microbes Description, General Properties, 33, 34 ; Plate I., Figs. 4, 5 and in Milk, 174 Saliva, 210, 231 Urine, 840, 284, 285 Microscopical Examination of Urine, 269 to 886 Acid Urates, 270 Ammonium Urates, 273 Calciun\ Carbonate, 273 Calcium Oxalate, 270 Calcium Phosphate, 273 Calcium Sulphate, 271 Casts, 275 Cystin, 274 Epithelial Cells, 283 Foreign Bodies, 285 Hippuric Acid, 271 Leucin and Tyrosin, 273 Microbes, 284 Pus Cells, 280 Red Blood-Cells, 279 Spermatozoa, 284 Triple Phosphate, 272 Uric Acid, 279 Milk, 173 to 186 ; also 39, 59 Adulteration of, 177 to 182 Breast, 173, 174, 181, 182, 185 Casein, 72, 175, 184 Composition, 172 Cows, 173, 184 Experiments, 184, 185 Human ; see Breast Koumyss, 183, 184, 180 ; also 18, 39 Proteids in, 17'5 ; see also Casein Regulation of Traffic in, 178 to 182 Tests, 178 to 182, 184, 185 Milk Sugar or Lactose General Properties, etc., 38, 39, 170 in Urine, 259 Tests, 41, 185, 186 Millon's Reaction and Tests, 74, 81 for Albuminoids, 170, 171 for Proteids, 81, 88, 89, 97, 184 Mineral Waters, 1.57, 160 Molybdic-Acid Test for Alcohol, 45, 47, 186 Mono-Saccharids or Glucoses, 10 to 20 ; also see Dextrose, Glucose, Laavulose Moore's Test for Glucose, 19, 24, 260, 262 Mould Plants, .33, 284 ; Plate I., Fig. 4 Mucin, 7'3, 206 Murexide Test for Uric Acid, 251, 8.54 Myosin, 84, 85, 88 Nessler's Test for Ammonia, 151, 1.59 Nitrate of Urea, 848, 253 ; Plato VI., Fig. 2 Nitrates in water, 153, 154, 150, 159 Nitric Acid, 118 to 120, 121 to 123 Nitric-Acid Ring Test for Albumin (Hel- ler's Test), 193, 196, 250, 858 INDEX. 313 Nitrites in Water, 1" Nuclei'n, 73 ir>0, ir>9 Oils Castor oil, G3, 00 Cod-liver oil, 04, GO Olive oil, 03, GO Oleomargarin, 59, 05 Olive oil, 03, 00 Organized Ferments, 33, 34; see Bacteria, ]\licrobes, Mould, Yeast; Plate I., Figs. 4, 5, Ortho-Phosphoric Acid, V24, 130 Ossein, Collagen, 73, lOG, 170 t)xygeu, 103, 104, 110; also li)(), I'.it Pancreatic Juice, 'J24 to ~';;(i, t':!0; also 31, 33 Papain, 31, 33 Paraglobuliu, 85, 194, iro Pepsin, 31, 32, 218 to 221 Peptones, 72, 219, 223, 227 in Urine, 257 Peptonizing Ferments, 31, 32 ; see Pa- pain, Pepsin, Trypsin Peptonuria, 257 Pettenkofer's Test for Bile Acids, 207, 210 Phenyl-Hydrazin Test for Glucose, 19, 24, 200, 302; Plate I., Figs. 1 and 2 Phenol Test for Nitric Acid, 119, 122; also 21 Phloroglucin Test for free Hydrochloric Acid, 222, 229 Phosphates (Ortho-), Tests, 124, 130 ; Plate II., Fig. 2; Plate III., Figs. 2 and 3 iu Blood, 197,208 in Bone, 108, 109 in Jlilk, 170, 185 iu Urine, 243, 245, 272, 273 ; Fig. 19, p. 273; Plate VIII., Figs. A and B in Water, 155 Phosphoric Acid (Ortho-\ 124, 130 Picric Acid, 21, 119 Picric-Acid-and-Potash Test for Olucose, 21, 25, -200, 2G2 Picric-Acid Test for Albiiinin, 7(1, K2, 194, 196 Plant Albumins, 73, 93 Plant Casein, 73, 94 Plant Globulins, 73, 93 Poly-Saccharids, 4 ; see Cellulose, Dex- trins. Glycogen, Starch, etc. Potassium, 140, 143 Proteids or Albuminous Bodies, 00 to 90 ; see also Albumins, Fibrin, Globu- lins, Peptones, etc. ' Proteids, Cla.ssiflcalion, 71 Composition, 09 General Properties, 70 Occurrence, 09 Reactions, 81 Ptyalin, 31, a5, 217, 331 Pus Cells in Urine, 2f!0 to 2S3 ; Figs. 24 and 35, pp. 3S0 and 282 Red Blood-Cells, 198, 199, 270; Fig. 23. p. 279; Plates IV. and V. Rennet Ferment (Lab), 31, 32, 225, 2:^0 Resorcin and Sugar Test for Hydro- chloric Acid, 223, 229 Saccharifying Ferments, 31 ; .see Amyl- opsin and Ptyalin Saliva, 210, 217, 231 ; Fig. 10, p. 210 ; also 23, 31 Serum, 193, 195 ; also 78, 85 Serum Albumin General Properties and Reactions. '■8, 79, 82 in Blood Serum, 193, 195 iu Urine, 255, 258, 275 Soap, 54, 55, 57 Soap Test for Hardness, 148, 140, l.W Sodic Nitro-Prusside Test for Sulphur, 90, 99 Sod ic-Sulphate Reaction. 75, 81 Sodium, 139, 142 ; Plate III., Figs. 4 and 5 Sodium Chloride; see Chlorides Spectroscope, 200 Specti-um Analysis of Blood Stains, 200 Spermatozoa iu Urine, 284 ; Figs. 25 and 27, pp. 282 and 285 Spongin, 73 Starch Conversion of, into Dextrin, Glucose, etc., 9, 27, 28,31,34,35 Digestion of, 28, 31, 217, 224, 231 General Properties, Tests, etc., 8 to 1 1 Steapsin, 31, 32, 225, 230 Sulphates in Blood, 197 in IMilk, 177, 185 in Urine, 243, 245 in Water, 147, 148, 1.57, 1,58, ICI in Wood, 144 Tests, 115, 120, 121 Sulphuric Acid, 114 to 116. 120 ; Plate II., Fig. (Calcium Sulphate) Sulphur in Proteids, 95, 98 Syntonin, 87, 97; also 231, 223 Triple Phosphate, 125, 130, 130, 137, 2r2 ; Plate II., Fig. 2 ; Plate III.. Figs. 3 and 3 ; Plate VIU., Figs. A and B 314 INDEX. Trommer's Test for Glucose, 21, 25, 260, 262 Trypsin, 31, 32, 224, 230 Ultzmaxn's Test for Bile Pigments, 205, 210 Unorganized Ferments, 30 to 32 ; see also Amylopsiu, Diastase, Pepsin, Ptyalin, Rennet, Trypsin, etc. Urea, 246 to 250, 252, 253 ; also 173, 235, 237, 239, 240, 243 ; Plate VI., Fig. 1 Mercuric Nitrate, 248, 254 Kitrate, 248, 253 ; Plate VI., Fig. 2 Oxalate, 248, 253 ; Plate VI., Fig. 3 Sodium Chloride, 248, 253, 254 ; Plate VI., Fig. 4 Tests for, 248 to 251, 252, 253 ; Figs. 15 and 10, p. 252 Uric Acid, 250, 251, 254 : Plate VI., Figs. 5 and 6 Microscopical E.ramination for, 2li!i ; Plate VIII., Figs. A and B Urine, 235 to 286 Albumin in, 255 to 259 Blood, Pus, and Epithelial Cells in, !i79to284 Casts, 275 to 279 Color, 239, 244 Consistency, 239, 244 Formation, 235 to 2S8 General Chemical Properties, 343 Glucose in, 259 to 264 Microscopical Examination of, 267 to 287 Odor, 242, 245 Quantity, 838 Urine, Reaction, 240, 244 Sediments in Acid Urine, 269 to 272 Sediments in Alkaline Urine, 272 to 275 Specific Gravity, 238, 244 Spermatozoa, Microbes, and Foreign Bodies in, 284 to 287 Structiire of Kidney Tubules, 236, 237; Figs. 13 and 14, pp. 37, 237 Urea and Uric Acid, 246 to 255 Vegetable Proteids, 73, 92 to 95 ; see Gluten Vitellin, 80, 82 Water, 147 to 161 Albuminoid Ammonia in, 1.52 Ammonia (free) in, 151, 152, 159 Analysis of Croton, 156 Biological Tests, 149 to 151 Chemical Tests, 151 to 157, 159, 160 Chlorides in, 154, 155, 158, 160 Drinking, Tests on, 149 to 157 Hardness in, 147 to 149, 158 for Laundry or Manufacturing Pur- poses, 147 to 149, 158 Mineral, 157, 158, 160, 161 Nitrates in, 153, 159 Nitrites in, 152, 159 Wood Ashes, 141, 143 Xantho-proteic Reaction for Proteids, 74, 81 Yeast, .33, 47, 284 ; also 14, 17, 31, 38, 39, 41,42,43; Plate I., Fig. 5 October, 1892. 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