Columbia ^Hnibersitp in tjje Cttj> of Jgeiu gorfe COLLEGE OF PHYSICIANS AND SURGEONS Reference Library Given by '^ttzi^ QUESTIONS AND ANSWERS IN PHYSIOLOGICAL CHEMISTRY WITH COMMON TESTS, FORMUL.^, EQUATIONS AND PAST EXAMINATION PAPERS FOUNDED ON THE COURSE IN PHYSIOLOGICAL CHEMISTRY, GIVEN AT THE COLLEGE OF PHYSICIANS AND SURGEONS, COLUMBIA UNIVERSITY, NEW YORK CITY BY EDWARD C. BRENNER, A.B. NEW YORK PUBLISHED BY THE AUTHOR 1906 Copyright, 1906 By Edward C. Brenner Press of Th'. New Era pptNTiNe Compamv. LANCASTER, Pll. TO DR. WILLIAM J. GIES IN TOKEN OF THE MANY ACTS OF KINDNESS SHOWN THE AUTHOR PREFACE. This little book has been written to aid medical stu- dents in obtaining a clear and concise idea of the essen- tials of physiological chemistry. Special care has been taken to select for treatment such questions as best serve to make clear the fundamental principles. A few sentences have been copied verbatim from stan- dard authors. My reference works were: the notes and lectures of Prof. Gies and Prof. Chittenden, Hammar- sten's " Physiological Chemistry," Foster's and Kirke's '' Physiology " and Curtman's '* Urine Analysis." I owe my sincerest thanks to Dr. Gies, without whose kind encouragement this would not have been attempted. I am also under obligations to Mr. George H. Humph- reys for assistance in proof reading, and Dr. Harold M. Hays for many valuable suggestions. E. C. B. January, 1906. Questions and Answers in Physiological Chemistry. What is physiological chemistry ? Physiological chemistry is chemistry applied to life phe- nomena, or that department of physiology which depends upon chemistry. It is chemistry applied to organisms to understand their chemical changes of a functional character. What are the general characters of chemical change (a) in the living body, (b) in the dead organism, (c) in plants as contrasted with animals? (a) The living body is constantly taking in material and changing it, in a regular and orderly fashion. This metabolic process is one of analysis and synthesis, chiefly analysis, (b) In the dead organism, instead of this proc- ess proceeding in an orderly fashion, the changes occur promiscuously, and all result in converting the body into simpler materials. Thus in animals ther e_js_an^ orderly analytic and synthetic process ; in the dead organism, a diso rderT y an alytic . (c) Plants convert inorganic into organic compounds. This process is the maximum of synthetic operation. In animals, although there is con- siderable synthesis, analysis predominates. 4 PHYSIOLOGICAL CHEMISTRY. CARBOHYDRATES. What are carbohydrates? Carbo hy drates are organic compounds, forming the chief portion of^the dry substance ot plants. 1 hey occur, in the animal kingdom, in proportionately small quantities, either free or in combination with more complex mole- cules, forming compound proteids, as gluco-proteids. Carbohydrates contain only C, H, O, the latter two elements usually "" occur n ng^in^e^ as they ^o m water^ viz., 2 : T7 hence the name carbohydrates. They are readily convertible into other products, yielding much energy and heat. Hov^7 and where are carbohydrates derived from in- organic material? By synthesis in the chlorophyllic bodies, thus : CO2 + H2O = H.CHO + O2 6H.CHO = C6Hi206 (dextrose). What are the three chief groups into which carbo- hydrates are divided? Give examples of each group. I. Monosacch arides — , ^ " TDextrose (glucose) . «^ fc ^ ' ^^ ^ ^ a. Hexoses^ Levulose (fruit-sugar). I Galactose. { 1 Ti , 1 Arabinose. L. w^^^„ 2. Disaccharides — Maltose. Lactose (milk-sugar). Sucrose (cane-sugar). 3. Polysaccharides — Starch. . Dextrin. ft I4 () <- Glycogen (animal starch). (p ^0 '^ Cellulose. I 6 PHYSIOLOGICAL CHEMISTRY. What are the general qualitative tests for carbohy- drates? Describe each. 1. Molisch's. 2. Plenylhydrazine. 3. Moore's. 4. Iodine. 1. Molisch's Test. — To the sugar solution add a few drops oi alpha-naphthol, then cone. H2SO4 in excess. A red to purple color will result. This is a general test for all_ carbohydrates^ The reaction depends upon the forrnation of furKirol from the sugar by the H2SO4. The furfurol reacts with the alpha-naphthol, producing the purple zone. 2. Phenylhydrazine Test. — To the sugar solution add a ^ <- spoonful of sodium acetate with phenylhydrazine hydro- fl O chloride. Boil and allow to stand 24 hrs. Characteristic crystals will form. With the phenylhydrazine, the sugar first yields hydrazones, with the elimination of H2O, and upon further action, osozones. Most of the sugars in the body yield crystals with phenylhydrazine. 3. Moore's Test. — Add KOH to the sugar solution and heat. Yellow color results with a faint odor of caramel. This is a test for d extrose and disacc harides. 4. iodme 'lest. — Most "polysaccharides added to an iodine solution turn it blue. The color disappears on warming and reappears on cooling. What is meant by the " inversion of sugars " ? By '' inversion of sugars " is meant the hydrolyti^ cleavag^e of compound sugars into monosaccharides, thus : Sucrose + HgO = Dextrose + Leyulose. Maltose -j- H2O = Dextrose -|- Dextrose. Lactose -j- H2O = Dextrose -|- Galactose. What are the characteristics of monosaccharides? All are either aldehydes or ketones of polyhydric alco- hols and are termed aldoses and ketoses respectively, thus : Dextrose = CH2(OH).(CH(OH))4.CHO = aldose. Levulose = CH2(OH).(CH(OH))3.CO.CH2(OH)=ketose. u ..i-^^ LL>dt3tv 6-^^ - ^■^-'^^ PHYSIOLOGICAL CHEMISTRY. All are strong reducing agents due to the aldehyde or ketone raciical 1 hey are colorless, odorless ," neutral m reaction, easily soluble in HsQ^ difficultly soluble in alco- hol and insoluble in ether . They are optically active, fer- mentable and dittusible. With phenylhydrazine they yield characteristic crystals. What are the characteristics of disaccHarides ? They are soluble in dilute alcohol, diffusible, ferment- able and have reducing powers . With phenylhydrazine, they form crystals. They do not respond to the I reac - tion (sucrose is an exception in some cases ). All are converted' into" monosaccharides by hydrolytic cleavage. What are the characteristics of polysaccharides? Polysaccharides are characterized by general insolu- bility. ( Glj^co^en and dextrin_ are_ soluble. ) Most give the I color reaction or yieH "products"wh"ich y^ill. They d o not reduce , are i ndiffusible and non- fermentable and do not_ yield cry s ta ls y^it h phenylhydr azine. *" Allare ulti- mately converted into monosaccharides by hydrolytic cleavage. Write reactions to show: 1. Synthesis of a carbohydrate from inorganic radicals. CO2 + H2O = H.CHO + O. 6H.CHO = C6H,206 2. Production of a polysaccharide from inorganic radicals. a. 6CO2 -f 6H2O = CeHi^Oe -f-602 b. (CeHisOe — HoO)x= (C6Hio05)x+ (H20)x x:=not less than 5 3. Formation of CO2 from glycogen. CeHxoOs + I2O = 6CO2 + SH2O 4. Inversion of a disaccharide. C12H22O1X + H2O = CeHisOe -f- C9H12O6 V Q^t:uda ^^ijy ijOt^ <^^ ^ e. H H I • C W H 10 PHYSIOLOGICAL CHEMISTRY. 5. Regeneration of a polysaccharide to a monosac- charide. a. (CeHloOs) X + H2O = (C6Hio05)2.H20 + (C6Hio05)x-2 b. (CeHaoOs) 2.H2O = G2H22O11 C. Cl2i^ll + H2O = 2C6H12O6 6. Formation of a disaccharide from dextrose. 2C6H12O6 — H2O = C12H22O11 + H2O 7. Formation of glycuronic acid from dextrose. Dextrose Glycuronic Acid CH2OH + O CHO (CH0H)4 = (CHOH)4 + H20 CHO + O COOH FATS. What are fats chemically? Name the three chief body fats. Where are they found in the body? Fats are tri-glycerides, being composed of one radicle of glycerin and three of a fatty acid. The hydrogen atoms of the three hydroxyl groups are each replaced by a fatty acid radical. The three chief fats are tri-stearin, tri-palmatin and tri- olein. They are found as primary constituents of every cell. What are the leading properties of fats? fc. They are highly refractive^ crystallize in rosettes, and are insoluble in all the common reagents, except hot alco- hol and ether. They contain a small amount of O in proportion to C and H, and are easilv oxidized . All are saponifiable and relatively indiffusible. Tri-stearin and tri-palmitin are solid, tri-olein liquid, at ordinary tempera- ture. Human fat is 75 per cent, tri-olein. State the more important facts regarding the origin of fat from proteids. 1°. The putrefaction of proteid material is accompanied by the formation of fatty acids and glycerol. e ^ u^^ - (M^t. - '^ ''I ^3- » U ,iL.iA^ " *'^-^ d^ fc 30 PHYSIOLOGICAL CHEMISTRY. Salkowski's Reaction. — Dissolve the solid cholesterin in chloroform. Add an equal volume concentrated H2SO4. Shake thoroughly. The solution becomes a cherry red which gradually deepens in color. Cholesterin I odine Test. — Place a cholesterin crystal on a microscope slide and add a drop of tincture of iodine. Put on the cover slide and allow a drop of H2SO4 to ooze under. A series of colors, from brown through green to blue, will follow the line of advance of the acid. CHEMISTRY OF THE TISSUES. What are the characteristics of tendon? Tendon is a form of connective tissue whose chief con- stituent (one-third) is collagen. It contains little lymph and blood and has a passive mechanical function, being best adapted for weight and strength. Describe collagen. Collagen is an albuminoid, characterized by its tensile strength. Although it is very insoluble it is easily hy- drated, in warm water, to gelatin. Thus the collagen in tissues is quantitatively estimated by the amount of gelatin it yields. Upon being heated in acid, it swells up and, upon decomposition, shows the presence of S. It is di- gestible due to the fact that it is easily hydrated. Describe mucoid. How may it be prepared? Mucoid is a constituent of all forms of connective tissue, especially tendon. It is a compound proteid, gluco; £roteid, being composed of a proteid and a sugar-like radical. Upon decomposition by acid it yields H2SO4 instead of H3PO4 and no purin bases, thus : ' ' Gluco-proteid Proteid Chondroitin H2SO4 / \ Chondroitjn H2SO4 / \ Chondroisin Fatty acid (acetic) / \ Glucos-amine Glycuronic acid. cuiiujibU^ 9mMj^^ 32 PHYSIOLOGICAL CHEMISTRY. Preparation. — It may be extracted by dilute alkali, as lime-water, and precipitat^dTb^^^acid. Where does elastin occur? How may it be extracted? Give its properties. Elastin occurs in the connective tissues of higher ani- mals, sometimes in such quantities that it forms a special tissue. Ligamentum nuchge is one-third elastin. Extraction. — With water, wash the ligament free of blood. Put it in a dilute lime-water solution to dissolve out the mucoid. Then boil the ligament and filter while hot. Elastin remains on the filter paper. Properties. — It is insoluble in the usual reagents and is generally considered as a sulphur-free substance. It permits of great stretching. In tendon, over-stretching is prevented by the collagen. What is the chief constituent of epidermal tissue? Keratin. — It is a condensation product of albumins and globulins, being derived from the underlying cells. It is the chief constituent of the horny substance of the epi- dermis, hair, nails, hoofs and horns, and also occurs as neurokeratin in the brain and nerves. It is insoluble, being the most resistant of all organic material and is of no food value. When heated in a strong acid or alkali it will decompose. It is characterized by containing a large percentage of loosely combined S. How would you detect the presence of S in keratin? Decompose the keratin by boiling it in KOH. This liberates the S. Add a few drops of Pb acetate. A dark brown color results from the formation of Pb sulphide. Describe osseous tissue. Bone is a peculiar connective tissue, being characterized by great rigidity. It consists of an organic matrix im- pregnated with lime salts. If treated with dilute HCl, the inorganic substances are dissolved and the organic material remains as a soft, elastic mass, preserving the original shape of the bone. This organic matrix consists 34 PHYSIOLOGICAL CHEMISTRY. chiefly of ossein, a substance practically identical with collagen. It also contains mucoid and albuminoid. After complete calcination of the organic substance, a white, brittle mass remains. This represents the inorganic constituents which in some cases amount to 50 per cent, of the solid material. Bone is comparatively poorly supplied with blood- vessels and must be ranked with the chemically passive tissues. What are the chief inorganic constituents of bone? Ca, Mg, Na, K, Fe. P2O5, CI, CO2. Ca3(P04)2 predominates. Traces of sulphates and silicates may occur. Describe cartilage. Cartilage is in some respects similar to tendon, in others to bone. Like tendon it contains a large amount of col- lagen. It differs from bone chiefly in the amount of inorganic constituents. It is characterized by its content of chondroitin-sulphuric acid, uncombined with proteid, in the form of a Na or K salt. Its mucoid is spoken of as chondro-mucoid. Describe muscle. Muscle is composed of fibers (cells) bound together with little intercellular substance. Each fiber consists of a sheath, sarcolemma, composed of a substance analogous to elastin, and enclosing a homogeneous, semi-fluid sub- stance. Upon death, this viscid content solidifies (rigor mortis). Muscle has an abundant blood and lymph sup- ply and ranks as one of the most active tissues. What are the chief constituents of muscle? Muscle contains about 75 per cent, water, 18 per cent, proteid, 3 per cent, fat, 3 per cent, inorganic salts, 2 per cent; collagen, .2 per cent, extractives, and traces of gly- cogen. \hjAilh.--' ^'^^-V'"'*'*'^ 7,6 PHYSIOLOGICAL CHEMISTRY. Describe the chief muscle proteids. Like blood which contains a fluid (blood plasma), which spontaneously coagulates, separating fibrin and yielding blood serum, so living muscle has a coagulating liquid (muscle plasma) which spontaneously coagulates, separat- ing a clot, myosin (myosin fibrin) and also a serum. This coagulating process occurs soon after death, in rigor mortis, and is probably due to an enzyme. This myosin is a post-mortem product and is never present in living muscle. Its antecedents are myosinogen and para-myo- sinogen. Myosin is a globulin, constituting about 7 per cent, of the dead muscle ; it is soluble in 10 per cent. NaCl but is precipitated upon saturation. Concerning the stroma substance but little is known. It is insoluble in NaCl but soluble in dilute alkalies in which it is transformed into albuminate. The elementary composition is nearly the same as that of myosin. What can you say of the presence and significance of the inorganic salts and fat in muscle? The predominating inorganic constituents are K and phosphoric acid. Next in amounts are Na and Mg; traces of Ca, Fe and CI are also present. It appears that the combined action of these ions is necessary for the normal function of the muscle. Fat is present in variable quantities, both as inter- muscular and intra-muscular fat. The latter is within the sarcolemma and, due to its high calorific power, is the best form of potential energy the body has. What is the carbohydrate in muscle? Describe it. How does it get to the muscle? What results from its breaking down? Glycogen and glucose, into which it is transformed. Glycogen, first called animal starch, resembles vegetable starch in its physical and chemical characteristics, differ- ing chiefly in its coloration with I, giving a brownish-red color, and in being very soluble in water, producing a characteristic opalescence. Glycogen reaches muscle as sugar or as glycogen, itself, 5u1^4jua m 38 PHYSIOLOGICAL CHEMISTRY. coming from the liver where it is manufactured and stored. It is the leading fuel material of muscle. CO2 and H2O result from its breaking down. How may glycogen be extracted from muscle? Give its properties. Glycogen is present in all muscles but only in traces. It is most easily extracted from scallops which are practi- cally all muscle and contain much glycogen . Extraction. — Grind scallops with sand and place in casserole with water. Heat and stir constantly till boil- ing. Then add a few drops of acetic acid to coagulate any proteid not already coagulated. Filter. The filtrate is milky, due to suspended glycogen. Add alcohol and a white flocculent precipitate of glycogen will appear. Properties. — It is soluble in all the reagents except alcohol and ether, and, therefore, is soluble in all the body fluids. Its aqueous solution is characterized by opal- escence (Ex. = clam broth). It is readily converted into sugar and easily oxidized to CO2 and H2O. What are the chief extractives? Why is it important to know about these? The extractives are creatin, creatinin, xanthin, hypO- xanthin, guanin, and carnine. They are important be- cause they represent products of the changes which pro- teid material is undergoing. How would you obtain these extractives from muscle? Stir some hashed beef in a NaCl solution and allow to stand. Filter. Saturate the filtrate with NaCl. The floc- culent precipitate ^ m3/06-w. Filter. The filtrate con- tains all the extractives and the inorganic matter. To get rid of the inorganic radicles, add Pb acetate. The precipi- tate ^PbSO^, Pb3(P04)2 and PbCl2. Filter. H2S is run through to precipitate the Pb which is filtered off, leaving the extractives in solution. hjj^ 40 PHYSIOLOGICAL CHEMISTRY. What are purin bases? Illustrate by formulae. Purin bases are modifications of a compound, N = CH ! I CgH-N, orHC C — NH. II II >H N — C — N ^ called purin. The different purin bases are derived from purin by the substitution of the various H atoms by hydroxyl or other groups. In order to signify the different positions of substitution, the nine members of the purin nucleus have been numbered thus : 3N-C,-N/ Thus xanthin, 2, 6 — di-oxypurin is HN — CO CO C — NH. I II Vh HN — C — N ^ Hypoxanthin, 6 — oxypurin is HN — CO HC C — NH .1 ,. )CH N C — N ^ Uric acid, 2, 6, 8 — trioxypurin is HN — CO CO C — NH. I II >co HN — C — NH^ It is believed these purin bases are oxidized to uric acid and excreted as such. (jkiM^^ 42 PHYSIOLOGICAL CHEMISTRY. How may creatin be separated from the purin bases? With 88 per cent, alcohol which dissolves the purin bases without affecting the creatin. What is creatin? Illustrate by formula. Creatin is a nitrogenous body, methyl-guanidin-acetic acid, formed in muscle as a wear-and-tear product. It is closely related to creatinin which is creatin, dehydrated. Creatin is similar to urea, thus : Urea. Guanidin or imino urea. /NH2 /NH2 I. 0=C< II. NH3^C< \nH2 \NH2 III. Methyl guanidin, NH, NH = C< \NH(CH)3 IV. Methyl-guanidin-acetic acid --= creatin. NH, NH=:C< \n(ch3; Creatin by dehydration = creatinin, thus : /NH, NH=C<( /NH- \N (CH3) CH2COOH— H20=NH=C< I \N(CH3)CH2CO In the urine, it appears as creatinin. What is the reaction for creatinin? Describe it. Weyl's Reaction. — Make the creatinin solution alkaline with KOH. Add a drop of Na nitro-prussid. A red color results which is destroyed by acidification. Acetone responds to the test but the color does not disappear upon acidification (Legal's test). What is the food value of commercial meat extract? The extracts contain practically no proteid or fat, and but little carbohydrate. Hence, since food material, which yields energy, is mainly composed of proteid fat and car- ^fUKUA 44 PHYSIOLOGICAL CHEMISTRY. bohydrate, the extracts have no real food value. But they are medicinally valuable due to their contents of purin bases and inorganic salts, both of which serve as stimulants. The K salts are especially valuable as a heart stimulant. Meat, extracted in cold solution, would be of real food value as the extract would contain the three food stuffs. What is the reaction of living muscle, (a) at rest? (b) after work? Explain these phenomena. The reaction at rest is alkaline due to K2HPO4 the predominating salt; after work it is acid. During the breaking down of glycogen, synchronous with muscular activity, lactic acid is formed. This im- mediately reacts with the alkaline phosphate K2HPO4 transforming it into acid phosphate H2KPO4 by with- drawing basic ions for its own neutralization. That the acidity is due to acid salts and not free lactic acid, may be shown with lachmoid paper which does not change color except with free acids. Describe nerve tissue. Nerve tissue consists largely of connective tissue ele- ments which hold nerve cells and their processes. It contains, besides the general primary constituents, cer- tain highly specialized fatty substances, as cerebrin, choles- terin, lecithin, and protagon. The supporting proteid is neuro-keratin. These various constituents exist in the brain in loose molecular combination, and, it is believed, each mental propagation is due to a physical or molecular change in these. How would you separate lecithin, cholesterin and cere- brin from brain tissue? Describe cerebrin. Put the hashed brain in cold alcohol. This extracts the lecithin. (A small amount of cholesterin usually accompanies.) Upon evaporating the cold alcohol ex- tract, lecithin will remain. Cholesterin is best extracted with cold ether. Beauti- ful crystals appear upon evaporation. rt>(rf"flL4't U SA 46 PHYSIOLOGICAL CHEMISTRY. Cerebrin may be obtained from brain tissue from which the lecithin and cholesterin have been removed, by heating it with 95 per cent, alcohol. It separates out and goes into solution in the hot alcohol. Cerebrin is a N substance, free from P, and similar in physical properties to cholesterin. Like the fats, it is soluble in warm alcohol and chloroform, but differs in being insoluble in cold alcohol and ether. It contains a sugar-like radical and, upon decomposition, yields a fat and a carbohydrate (galactose). Indicate (a) the composition of liver; (b) its functions. Liver, like muscle, is about three-fourths water. Of the solids, 9 per cent, is proteid, 3 per cent, fat, glycogen in variable amounts and 5 per cent, extractives. It also contains ferratin (iron albuminate). The most important functions are : 1. Manufacture of bile. 2. Manufacture and storage of glycogen. 3. Formation of urea^, 4. Filtration and storing of heavy metals and albu- minoids. Hov^r may iron albuminate be prepared from liver? What is peculiar about the iron in that substance? Grind some hashed liver with sand. Transfer it to a casserole, one-half full of water, and gradually heat to boiling. This coagulates all the proteids except iron albuminate which is not coagulated by heat. Filter. The filtrate contains iron albuminate, glycogen and the ex- tractives. Acidify with tartaric acid and a flocculent pre- cipitate of iron albuminafe^wiir fall. The iron in this albuminate (ferratin) is closely com- bined with the proteid. It is so intimately combined with the proteid radical that it will not respond to iron tests without previously being split off by decomposition. This ferratin and hemoglobin are the only two compounds in the body containing iron combined in an organic compound. (UtOA 5>% 3tc^. ^ ^rlkjiMiM ^ S^xha QMum^jjM^ 48 PHYSIOLOGICAL CHEMISTRY. BLOOD. What are the chief chemical constituents of blood? I. Proteids. "Serum albumin. "^ Serum globulin. — Fibrinogen ( globulin ) . Nucleo-proteid. Hemoglobin. , Fats, soaps and free fatty acids. JL 2. 3- Carho hydrates. ^ Dextrose. 4. Inorganic salts. Alkali phosphates, chlorides, sulphates, and car- bonates, of Ca, Mg, Na, K and Fe. What is the specific gravity and reaction of blood? Is the coloring matter in the plasma or corpuscles? Prove by experiment. Which are larger, the cor- puscles of warm- or cold-blooded animals? Cite an experiment to illustrate this. Specific gravity averages 1058 (highest specific gravity of any body fluid). Reaction, alkaline, due to alkaline phosphates and carbonates. The coloring matter is in the red corpuscles. If frog's blood be filtered, the red coloring matter (corpuscles) will be left on the filter paper and the filtrate will be almost colorless. The corpuscles of cold-blooded animals are the larger. When human blood is filtered, the corpuscles pass through, proving they are smaller than the pores of the filter paper. Frog's corpuscles will not go through. What are prothrombin, thrombin, fibrinogen and fibrin? Prothrombin is the hypothetical mother substance of thrombin, or fibrin ferment. Thrombin is synonymous with fibrin ferment and is a nucleo-proteid, the result of the influence of soluble Ca salts upon prothrombin. Fibrinogen is a globulin and has its origin in the destruc- 50 PHYSIOLOGICAL CHEMISTRY. tion of leucocytes. Fibrin is a coagulated proteid result- ing from the action of fibrin ferment upon fibrinogen in the spontaneous coagulation of blood. By what tests would you detect the presence of blood in a stain? 1. Dissolve a portion of the stain in a few drops of glycerin and in a few moments examine under the micro- scope. The corpuscles, if present, will be shrunken. 2. Dissolve the rest of the stain in water, making a concentrated extract. Place some before the spectroscope and observe if the two specific absorption bands, charac- teristic of hemoglobin, are present. 3. Guaiacum Test (for hemoglobin). To a very weak solution of the suspected blood, add a few drops of guaia- cum tincture and, then, a few drops of old turpentine (containing ozone). A bluish ring results at the zone of contact if hemoglobin is present. This test does not con- clusively prove the presence of hemoglobin, as pus and other substances will give the reaction. 4. Hemin Test. — An absolute test for blood. To a drop of suspected solution on a slide glass, add a minute grain of NaCl. Dry carefully over the flame ; when perfectly dry, add a drop of glacial acetic acid ; cover with cover glass and gently warm. When cool, examine under mi- croscope for hemin crystals. The acetic acid splits up the hemoglobin into globin and hematin. The NaCl reacts with the acetic acid form- ing Na acetate and nascent HCl. The HCl unites with the hematin forming hematin hydrochloride = hemin (chocolate color crystals), thus: Hemoglobin CH3COOH NaCl / \ / \ / \ Globin Hematin CH3COO ; H cl | Na How may the coagulation of blood be (i) retarded, (2) accelerated? Retarded by Accelerated by 1. Cold. I. Warming slightly. 2. Addition of K oxalate. 2. Contact with foreign bodies. k 52 PHYSIOLOGICAL CHEMISTRY. 3. Addition of strong salts. 3. Small amount of water. 4. Addition of much H2O. 4. Admission of air. 5. Superabundance of CO2 (as- 5. Diseases of the intima. phyxia). 6. Injection of peptone, 7. Electric current. Describe the method for detecting the blood of a cer- tain animal. Precipitin Test. — Blood of one animal is repeatedly injected, in small amounts, into the system of an animal of a different species. If, after several inoculations, some of the blood or serum of this " adapted " animal is mixed with the blood or serum of an animal of the first species, a precipitate will form. FOODS. What is the relative food value of carbohydrates, fats, and proteids? The value of a food depends upon: i. The amount of energy it will yield the body. 2. Its ability to form tissue. Fats and carbohydrates are heat producers, the former represents the body's store-house of energy, and carbo- hydrates, its immediate supply. Proteids figure mainly in tissue production. All struc- tural materials contain N and hence in the repair and building of structural elements, proteid food is absolutely essential. Without some, the animal cannot exist. MILK. !^^^3 M- Uxu -Ihaa QMdi iji^OAk^. \U"t y 56 PHYSIOLOGICAL CHEMISTRY. mediate precipitate of casein will follow. The filtrate is the whey. A. Name the leading constituents of (a) wheat flour, (6) potato, (c) bread. B. How may the most important in each be identified? (a) Wheat flour | l^^^'^J' (proteid). {h) Potato- Starch. Proteid. Fat. K2HPO4. (c) Bread — Starch. Dextrin. Proteid. Fats. Starch is most conspicuous in each. It may be identi- fied by the I test. What changes does flour undergo in its conversion into bread? 1. The starch granules are disrupted, the cellulose cap- sules being broken. 2. Porosity is produced. 3. The gluten is much swollen. 4. Some starch in the crust is transformed into dextrin. What is the leading constituent of lemon? How may * it be extracted? Do organic acids increase the t acidity of the urine? Citric Acid. — To filtered lemon juice add CaCOg till neutral and warm on water bath. Calcium citrate and CO2 are formed. Add a small amount of water and 5 c.c. diluted H2SO4. CaS04 precipitates out and citric acid remains in solution. Filter. Evaporate the filtrate to small bulk and citric acid will crystallize out on cooling. No. Citric acid and similar organic acids are converted into carbonates and bicarbonates and increase the alka- linity of the urine. 58 PHYSIOLOGICAL CHEMISTRY. DIGESTION. What is digestion? Digestion is a process by which food materials are trans- formed into substances capable of being utiHzed by the body. The nutritious elements are separated from the useless, the latter being excreted. What are the various kinds of digestion? Salivary, gastric, pancreatic, intestinal and bacterial. What are zymogens, enzymes, anti-enzymes and anti- toxins? Also their chemical function. Zymogens occur in the cells as the predecessors of en- zymes and are transformed by special influence into en- zymes. Thus, pepsinogen is the zymogen of pepsin. Enzymes are unorganized ferments, products of the chemical processes in cells. No enzyme has ever been separated and analyzed in a pure state and hence their elementary composition is unknown. They are catalytic agents, their action depending upon — 1. Reaction of the solution. 2. Temperature. 3. Presence of H2O. 4. Removal of the products of the reaction. Anti-enzymes are the antagonists of enzymes, having a neutralizing effect upon enzymes. Thus, a stomach ex- tract will destroy the action of enzymes of the stomach. If it were not for these anti-enzymes, the stomach would probably digest itself. Anti-toxins are unorganized ferments existing in the wall of the lower part of the alimentary canal and are antagonistic to all toxic elements entering the canal. ed(t&|iua0 biJr&jjiOt ^\Lxyi.(i..'X 6o PHYSIOLOGICAL CHEMISTRY. SALIVARY DIGESTION. What is salivary digestion? Salivary digestion is essentially a digestion of carbo- hydrates. Polysaccharides are transformed through the action of ptyalin into disaccharides, and a small amount of disaccharrde7~due to an invertin, into monosaccharide. Proteids, fats and inorganic salts are not affected. What is saliva? What are its constituents? Saliva is a mixture of the secretions of the submaxil- lary, parotid, sublingual, and buccal glands. Physical Characteristics. — It is a colorless, translucent liquid and when poured from one vessel to another is glairy and somewhat viscid. Chemical Ingredients, — Its reaction is alkaline due to alkaline phosphates and carbonates. The total solids are .5 per cent. Of these, the organic constituents are mucin,^ coagulable proteid, epithelial cells and bacteria. The inorganic materials are HoO, salts of the alkaline and earthy metals, phosphates, chlorides, sulphates, and potas- sium sulfo-cyanide. Enzymes. — Chief enzyme is ptyalin. An invertin is also present in small amounts. How would you test for the presence of (a) mucin, (h) coagulable proteid, {c) potassium sulfo-cyanide? (a) To a small amount of saliva, add a few drops of acetic acid. The precipitate is mucin, a gluco-proteid. (&) Heat. A slight opalescence results. {c) Put a few drops of saliva in a porcelain dish (crucible). Add a drop of dilute HCl and dilute ferric chloride. A red color results. The amount of potassium sulfo-cyanide is increased after using tobacco. Describe the enzyme ptyalin. Ptyalin is an amylolytic enzyme and converts starch into dextrins and sugars. It acts best in a neutral solu- tion, though dilute alkaline solutions, as saliva, do not impair its action. Mere traces of acid do. 62 PHYSIOLOGICAL CHEMISTRY. What is the effect of temperature upon the action of ptyalin? Cold retards its action and much heat completely de- stroys the enzyme. The optimum temperature is about 40° C. This is the general case with enzymes — cold re- tards but heat " kills." Give a table of the breaking down of starch in salivary digestion. Starch Soluble starch -I Erythrodextrin "f Achroodextrin 111 Maltodextrin —I Maltose r; • > Maltose I I (Invertin) Glucose Glucose H2O I Iodine. Fehling's Sol. Blue Blue Red GASTRIC DIGESTION. What is gastric digestion? Gastric digestion is essentially a digestion of proteids. Fat also is slightly emulsified due to the digestion of pro- teid capsules inclosing fat globules. The food is con- verted into a pulpy mass called chyme. What is the composition of gastric juice? Like saliva, it is about 99.5 per cent, water. It is dis- tinctly acid, due to HCl of a strength approximately .2 per cent. The important enzymes are pepsin and rennin . Lipase and an invertin are present in smalFamounts. 64 PHYSIOLOGICAL CHEMISTRY. How would you prepare a gastric extract and at the sanie time illustrate peptic digestion. Cover the mucous membrane of a pig's stomach with 4 per cent. HCl. The mucous membrane contains pep- sinogen, the zymogen of pepsin. When acid and pepsino- gen come into contact, pepsin results. This converts the proteids of the membrane into soluble materials (diges- tion) without affecting the strength of the pepsin. Can dilute HCl alone digest proteids? Can pepsin? No. If fibrin is put in a .2 per cent. HCl solution, it merely swells up. Pepsin, alone, has absolutely no effect on proteids, but must act in an acid medium. A solution of pepsin and HCl is called '' pepsin — HCl." Is the HCl in a free or combined state? What tests would you employ to prove the presence of free HCl? In health the HCl is partly free and partly combined with proteids. That which is in proteid combination is nevertheless physiologically active. Giinzberg's and the Tropaeolin OO test (for description see chapter on Common Tests). What functions may be ascribed to the HCl of gastric juice? 1. The most important function is the destruction of micro-organisms entering with food. 2. It converts pepsinogen into pepsin. 3. Assists pepsin in converting the proteids. 4. Slightly favors the conversion of starch into sugar. 5. Causes collaginous materials to swell and become gelatinized. Collaginous materials unless thus trans- formed are indigestible. 6. Converts prosecretin into secretin. 7. Increases the flow of pancreatic juice. What substances give rise to HCl? The most plausible theory is that NaCl is disintegrated by large amounts of COo, thus, NaCl -f- CO2 + H2O = NaHCOg + HCL. The bi-carbonate may also react with the salt, thus, NaHCOg + NaCl = Na^COg + HCl. 66 PHYSIOLOGICAL CHEMISTRY. In substantiation of this theory, the urine, soon after meals, becomes alkaUne, as would be expected from the alkaline carbonates being thrown back into the blood. Describe pepsin. Give a table showing its stages of digestion. Pepsin is a proteolytic enzyme, inactive in neutral or alkaline solutions, but in acid solutions, preferably HCl, it is very energetic. It converts proteids into a number of substances, the simplest of which is peptone, thus : Proteid. I Acid-proteid (albuminate). / \ Proto-proteose. Hetero-proteose (primary proteose). Deutero-proteose. Deutero-proteose (secondary proteose). " Peptone. Peptone. How can you separate proteoses from peptones? Take the solid composed of these two substances and add water. Boil on the water bath, adding (NH4)2S04 to saturation. A gummy precipitate of proteose will form on top. The proteose precipitate will cling to the stir- ring rod and the sides of the vessel. The peptone remains in solution. Pour off the liquid, clean out the vessel and dissolve the gum in boiling water. This will be a proteose solution. There are two kinds of proteoses in general — primary and secondary. The primary are precipitated by concen- trated HNO3, acetic acid and K ferro cyanide, while the secondary are not. Both are precipitated by picric acid and K mercuric iodide with HCl. What is the effect of acids and alkalies on gastric di- gestion? Also of heat and bile? A small amount of alkali destroys the action of the gastric enzymes. Dilute acids, except oxalic, and neutral salts do not affect them. Bile retards their action; ex- cessive heat (70° C.) kills the enzymes. ^u>^"-H 6 W -h ^0 H i-O ft a r 68 PHYSIOLOGICAL CHEMISTRY. Write a table illustrating the different effect of acid and alkali upon pepsin and its antecedent, pep- sinogen. 1. 8. 3. 4. 5. Glycerin Ext. Glycerin Ext. Glycerin Ext. Glycerin Ext. Pepsin Solution. Fibrin. 0.2 /„ HCl Fibrin. csf^Na^COs Fibrin. Fibrin. Eq. Vol., 15^ Na.COa Fibrin. No Digestion Digestion. No Digestion. No Digestion. No Digestion. Eq. Vol. 0.45^ Neutralize + Neutralize + Neutralize + HCl Eq. Vol. 0. 4i HCl Eq. Vol. o.4iHCl Eq. Vol o.4$HCl Digestion. Digestion. Slight digestion? No Digestion. Compare 3 and 5. The glycerin extract contains the zymogen, pepsinogen, which is not destroyed by the dilute alkali, whereas the pepsin itself is destroyed. What is rennin? Can it act alone? Rennin is an enzyme which has a pecuHar action on milk, converting caseinogen into casein, thereby pro- ducing the " curd." Yes. It coagulates the milk and prepares it for the action of the pepsin (HCl). What substances are to be tested for in stomach analy- sis? How would you identify each? First, test the reaction of the contents. Filter and test for free HCl. Under the microscope, note the kind of bacteria, fungi, cells, etc. Divide the filtrate into two parts and neutralize one portion. Filtrate. Neutralized — Test for— Unchanged— I, Albuminate. I. Pepsin. 2. Proteose. 2. Lactic acid 3. Peptone. 3. (Bile). 4. Ptyalin. 5. Rennin. 6. Sugar — Reducing agents. 7. Starch. -Test for- 6 ^i./vA.o.J iiiJA^i^tfjOft K N .? iUjM«;u' JuM«£cUt^ 70 PHYSIOLOGICAL CHEMISTRY. If, on neutralizing, there is a precipitate, albuminate is present. Saturate a portion with (NH4)2S04. The gummy precipitate is proteose. Filter. Test filtrate with Biuret test. A pink coloration indicates peptone. Test a fresh portion for ptyalin by trying to digest starch with some of the solution. To another portion add some milk. If there is curdling rennin is present. Test for sugar with Fehling's solution, starch with I test. To test for pepsin, add to a portion of the unchanged filtrate some fibrin in a 0.2 per cent HCl solution. Di- gestion indicates pepsin. For lactic acid, treat the re- mainder with carbolo-chloride of iron (Uffelmann's test). If lactic acid is present, the color disappears from the solution. PANCREATIC DIGESTION. Describe pancreatic juice. Pancreatic juice is a liquid containing from 4-10 per cent, solids. Its important constituents are an albumin, similar to myosin, giving rise to clotting, small amounts of fats and soaps, and a comparatively large amount of Na^COo (5 per cent.) to which is due the alkalinity of the juice. There are five enzymes (or their zymogens), three of which are important, trypsin, amylopsin, and lipase or steapsin. Invertins and rennin are present in small amounts. The juice is remarkable for the power it possesses of acting on all three foodstuffs, starch, fat, and proteid. (a) What is trypsin? Describe its action, {h) How does it differ from pepsin? {a) Trypsin is the proteolytic enzyme of pancreatic juice. It digests proteids in alkaline, neutral or very faintly acid solutions. {h) Peptic digestion is essentially an acid digestion, tryptic alkaline. In pancreatic digestion, the proteid dissolves without previously swelling up as in gastric digestion. \ XxJv AiAA,'-^ 72 PHYSIOLOGICAL CHEMISTRY. The essential difference is that in gastric digestion, the products are not carried beyond the proteid stage; in pancreatic digestion, much of the proteid is transformed into something which is no longer proteid. Therefore, tryptic digestion puts on the finishing touches to the work begun in gastric digestion, thus : Gastric Digestion. Pancreatic Digestion. Proteid. Proteid. I I Acid Proteid. Alkaline-Proteid. „ I I Proteose. Proteose. „ I I Peptone. Peptone. / \ . Lysin. Leucin. Arginin. Tyrosin. Histidin. Tryptophan, etc. What is the effect of various chemicals on tryptic digestion? Free acids prevent digestion. Metallic salts retard, while ordinary neutral salts, in small amounts, do not affect its action. Alcohol, ether, chloroform and bile, when not present in excess, have no harmful effect. What is lipase? Describe its action. Lipase is the fat-splitting enzyme of pancreatic juice. Its action is two-fold. First, it emulsifies fat and secondly, has the property of splitting neutral fats into glycerin and fatty acid. What is amylopsin? Describe its action. It is an amylolytic enzyme, being a sort of concen- trated ptyalin. Its action is the same as this substance, carrying on the work of digesting carbohydrates not already completed by saliva. On starch, it acts with great rapidity, converting it into sugar, chiefly maltose. The invertins in the pancreatic juice most probably convert the maltoses into dextrose. 74 PHYSIOLOGICAL CHEMISTRY. What are the functions of (a) secretin, (b) entero- kinase (c) erepsin? Secretin is formed by the action of HCl on the pre- formed prosecretin in the intestinal cells. It is absorbed into the blood and upon reaching the pancreas, stimulates its secretion. Enterokinase, a product of intestinal secretion, con- verts trypsinogen into trypsin. Erepsin converts peptones into nitrogenous crystalline bo3t^54rsr^leucin, tyrosin, tryptophan, etc. Perhaps tryp- sin does not transform proteid beyond the peptone stage ; in this case, erepsin is a necessary adjunct. What are leucin and tyrosin? Write their constitu- tional formulae. Leucin and tyrosin are two of the end products of pan- creatic digestion. They are nitrogenous crystalline bodies and, under the microscope, exhibit characteristic crys- tals; those of leucin are globular, tyrosin crystals ap- pearing as bundles of needles (sheaves). Leucin is amino-iso-butyl-acetic acid or amino caproic acid. CHq CHq \/ GH CH, • or C.uy I \COOH COOH Tyrosin is oxy-pheno!^amino-propionic acid. /OH QH / NH, \qH3/ \COOH What is Hofmann's test? Hofmann's test is a test for tyrosin with Millon's reagent. A beautiful red color results due to the phenol radicle in tyrosin. o A e H "J^y PHYSIOLOGICAL CHEMISTRY. What is the destiny of the various enzymes? Ptyalin is completely lost after it passes into the py- loric end of the stomach. Pepsin disappears after its entrance into the duodenum. The pancreatic enzymes cease to act before reaching the rectum. The only en- zymes in the faeces are those of bacteria. Occasionally enzymes appear in the blood and urine. BILE. Describe bile. Bile is a juice secreted by the hepatic cells. Its secre- tion is continuous, the fluid being stored in the gall blad- der until required in the intestines. When fresh, it is a bright golden yellow, changing to a green after reten- tion in the gall bladder. From the bladder it acquires a colloidal material, mucin, giving the fluid a '' thread pull- ing," ropy character. What is the composition of bile? It is an alkaline fluid, containing about 15 per cent, solids. The substances giving the character to it, are the bile salts and bile pigments. In addition it contains in- organic salts, cholesterin, lecithin and soaps. What is the influence of bile upon digestion? Bile contains no enzymes and hence is not strictly a digestive juice. But due to its salts, it favors digestion by having a two-fold action on fats. First, it emulsifies them, paving the way for the action of lipase in splitting fats into glycerin and free fatty acids. The Na of the bile salts then unites with the free fatty acids, forming soaps, which soaps in turn aid the further emulsion of fats ; secondly, bile favors the absorption of fats. Hence, it is an important adjunct to pancreatic juice in aiding both the emulsification and absorption of fat. What are the functions of bile? The functions of bile are : 1. To dissolve and emulsify fats. 2. To hold soaps in solution. 78 PHYSIOLOGICAL CHEMISTRY. 3. To aid in the alkalinity of the intestines and thereby prepare the way for the action of pancreatic juice. 4. To hold cholesterin in solution. 5. To serve as an excretory medium for cholesterin, pigments and metallic substances. /5. To stimulate the flow of trypsin. 7. To stimulate the flow of bile. 8. To stimulate the flow of intestinal fluids. \^. To promote peristalsis. 10. To act as a preventative agent of putrefaction. 11. To precipitate proteoses. "v 12. To favor the action of amylopsin. What are the bile salts? Write the constitutional for- mulae of glycocoU and taurin. The two bile salts are Na glycocholate and Na tauro- cholate. They consist of Na and the conjugate cholic acid united with glycocoU and with taurin. GlycocoU is amino-acetic acid. \COOH Taurin is amino-ethyl-sulphonic acid, so/ \0H What is the test for bile salts? Pettenkofer's Test. — To some bile in a porcelain dish, add a grain of sugar. Then drop in, from a pipette, concentrated H2SO4. A brilliant cherry-red color results. The H2SO4 disintegrates the bile salts and attacks the sugar, making furfurol. This furfurol and the cholic acid react to produce the red coloration. What is (a) the function of these bile salts? (b) their destiny? The various functions above attributed to bile are due to these salts. S-^j e ^ ^ C ) ^^ 1 ^ -r 5- I ^ 'j' ^ S <^ li ^ ^ o ^ 1^ v> 8o PHYSIOLOGICAL CHEMISTRY. Most of the bile salts are absorbed by the intestines (bile is a good cholagogue). The remainder is decom- posed by the HCl from the stomach as follows : Bile salts (Na) + HCl. / I \ Glycocoll NaCl Cholic acid Taurin Practically all the glycocoll and taurin is absorbed to form more bile salts. The rest of the glycocoll and taurin appears in the urine respectively as hippuric acid and indican. The cholic acid is dehydrated through choloidinic acid to dyslysin thus : Cholic acid C24H40O5 — H2O = Choloidinic acid C24H38O4 — HgO = Dyslysin C24H36O3 This dyslysin is excreted in the faeces. What are the bile pigments? The two normal pigments are bilirubin (red) and bili- verdin (green). BiHcyanin (blue), bilipurpurin (pur- ple), and bilixanthin (reddish yellow), are oxidation products of the two normal pigments. What is the test for bile pigments ? Gmelin's Test. — To a small amount of bile, in an evaporating dish, add from time to time, with the aid of a pipette, a few drops of nitric acid containing nitrous acid. There will be a series of colors beginning with green and passing through blue, violet and red to reddish- yellow. These successive colors result from the oxida- tion of the pigments, due to the nitrous acid. What is the origin of the pigments? What reason would you give to confirm this con- clusion ? The pigments result from the destruction of the hemo- globin of the blood. The relation of bilirubin to hemo- globin is as follows : (h^^JiUbi last- ~ d^^ p /QL-<4jUsL=:*^' 82 PHYSIOLOGICAL CHEMISTRY. Hemoglobin. / \ " Globin." Hematin, C32H3oN404Fe — Fe + 2H2 O 2 I a2H36N406 C16H1SN2O3 = bilirubin. Thus by the addition of two molecules of water the hemoglobin is transformed, after throwing off its iron component, into bilirubin. This view is supported by the fact that 1. The hepatic cells contain a peculiar iron content (ferratin). 2. Animals containing no hemoglobin in their blood, secrete no bile pigments. 3. If hemoglobin be injected into the blood, there will be an increase in bile pigments. 4. Hematoidin (found in black eyes, old blood clots, etc.), and bilirubin have the same formula. ABSORPTION, BACTERIAL DIGESTION AND FAECES. What changes, if any, do water and salts undergo in digestion? Water is merely warmed before being absorbed by the intestines. From them, it passes directly into the blood. Saline substances are not much affected. They may be converted from acid into alkali or vice versa, depend- ing upon the action of the digestive medium. They are usually absorbed in molecular form. (Organic acids all undergo essentially the same decom- position and are absorbed as salts, usually of Na. They are utilized in combustion, carbonates resulting, thus help- ing to maintain the normal alkalinity of the blood.) - 9-ja- -1-1/4 t,o 84 PHYSIOLOGICAL CHEMISTRY. Indicate the nature and extent of the chemical changes which carbohydrates undergo until they or their products are absorbed and transformed in the liver into glycogen. In salivary digestion, starch is acted upon. This ac- tion continues for some time in the cardia of the stomach, maltose being the final product. The little invertin in saliva may convert a trifle into glucose. Some of the starch thus passes into the intestine as maltose, but much has to be transformed by amylopsin, yielding malt- ose as the final product. The pancreatic invertins^ con- vert the maltose into glucose. Disaccharides are^ot af- fected until they reach the small intestine, where the pancreatic invertins transform them into monosaccharides as follows : Lactose Sucrose Maltose / \ / \ / \ Glucose Galactose Glucose Levulose Glucose Glucose Carbohydrates are absorbed as monosaccharides and appear as such in the blood. Reaching the liver by the portal vein, the glucose, by dehydration and polymeriza- tion, is converted into glycogen, which substance is the ultimate product of carbohydrate digestion. Carbohydrates normally undergo certain fermentations in the stomach, yielding CO2, alcohol, acetic, tartaric, and butyric acids in minute quantities. In indigestion, there is a superabundance of these. Fermentative proc- esses increase after leaving the stomach, but are less harmful in the intestines. In the large intestine of herbiv- orous animals, there is extensive fermentation to con- vert cellulose into soluble materials. State the changes which fats undergo from their en- trance into the body until their appearance in the lacteals. In the mouth, fats are melted and in the stomach, the peristaltic action makes a crude emulsion of them. A very slight change to glycerin and fatty acid may occur due to traces of lipase. 86 PHYSIOLOGICAL CHEMISTRY. In the intestines, upon meeting the alkaline pancreatic juice, bile, etc., further emulsion takes place. Due to the action of lipase, the fats are dissociated into glycerin and free fatty acids. Some free fatty acid unites with the alkalies, forming soaps, chiefly Na. Due to the bile, soaps, glycerin and fatty acids are kept in solution. It is believed that fat is absorbed in these forms, namely, glycerin, fatty acid, and soap and synthesized again, in the columnar cells, into neutral fats. From these cells it passes, as minute droplets, through the reticular tissue of the villi, to the lacteals. Trace, step by step, the changes that proteid food undergoes in its conversion into serum albumin. The first changes occur in the stomach, due to pepsin. Some of the proteid is converted through the stage of acid albuminate into primary and secondary proteose and into peptone. Some of the proteose and peptone is ab- sorbed in the stomach, appearing in the blood as serum albumin. The remaining proteid material ejected from the pylorus is acted upon by trypsinogen and is converted into proteose and peptone. Most of the proteose and peptone is absorbed as such, appearing in the blood, not as proteose and peptone, but serum proteid. But tryp- sinogen, in conjunction with erepsin, converts some of the proteose and peptone into products that are no longer proteid, namely, into nitrogenous crystalline bodies as leucin, tyrosin, tryptophan, etc. These crystalline products rapidly disappear from the intestinal fluid but cannot be detected in the intestinal wall or blood-vessels. Instead, there is, in the blood, an increase of serum albumin. Evi- dently these substances are immediately reconstructed in the intestinal epithelium into serum albumin. Just as carbohydrates undergo bacterial changes, called fermentation, so proteids undergo similar changes termed putrefaction. The characteristic products of intestinal putrefaction are : Reducing Gases. — CO2, HoS, CH4, NH3. Aromatic Bodies. — Indol, skatol, phenol and para- kresol. PHYSIOLOGICAL CHEMISTRY. Write the formulae for indol, skatol, phenol and para- kresol. What becomes of the indol and skatol? CH C(CHo) CJL CH QH, CH NH NH Indol. Skatol or methyl-indol. H CH, OH OH Phenol. Parakresol or methyl-phenol. Some of the indol and skatol is excreted in the faeces, giving to them their characteristic odor. The rest of the indol is absorbed and, reaching the liver, is hydrated to indoxyl. This indoxyl unites with a sulphuric acid radical, forming indoxyl-sulphuric acid. This, in turn, associates itself with an alkali, forming an indoxyl salt. This salt passes into the urine and is called indican. Skatol has a similar destiny. Write formulae to show the formation of indican from indol. CH C-OH /^ / ^ I. C,H, CH 2. CgH, CH \/ \ / NH NH Indol. Indoxyl. CO-SO,H co-rsOgK) / ^ /X CeH, CH 4. CfiH, CH \ / \/ NH NH [ndoxyl H2SO4. Indican. (a) Name the chief constituents present in normal faeces. (b) Explain the occurrence in the faeces of five of these. In the faeces are found : I. Digestible constituents of food — muscle fibres, con- nective tissue fibres, starch grains and fat. 90 PHYSIOLOGICAL CHEMISTRY. 2. Indigestible bodies as keratin. 3. Constituents of different secretions — dyslysin, mu- cin, cholesterin (stercolin). 4. Products of putrefaction or digestion — indol, ska- tol, phenol, parakresol, HgS, NH4 and mineral bodies as MgNH^PO^ and calcium and magnesium soap. 5. Alicro-organisms of various species. (b) I. All the digestible constituents have not had sufficient time to be completely digested in the intestinal tract. 2. The indigestible substances have not been affected by the various juices and hence not prepared for ab- sorption. 3. The presence of the secretory constituents shows that the faeces is an important channel for the exit of extraneous secretions. 4. The products of putrefaction result from the action of bacteria on proteids. 5. The micro-organisms are taken in with the food. Most are killed in the stomach by the HCl but some pass through the pylorus, mostly as spores. These germinate and the bacteria continue to flourish in the remainder of the intestinal tract. URINE. Why is the chemical study of urine important? Because of the light it throws on the metabolic pro- cesses of the body in health and disease. The constitu- ents represent end products formed all over the body (note the entire absence of the three kinds of food- stuffs). What are the chief constituents of urine? The (average) daily quantity of solids is 60 grams. Organic Bodies. — By far the most important is urea, constituting one-half of the total solids. Closely allied to urea, is uric acid, occurring in small quantity. Creatinin, hippuric acid, indican and the purin bases, (xanthin and hypoxanthin) are present in small and variable amounts. y ^ 92 PHYSIOLOGICAL CHEMISTRY. Inorganic Constituents. — The chief bases are Na, K, Ca, and Mg in the form of chlorides, phosphates, sul- phates and oxalates. NaCl is the most abundant and important, constituting 25 per cent, of the total solids. What is the quantity of urine used for analysis? Why this quantity? The quantity taken is what is called a " 24 hour " urine, meaning the amount excreted in that many consec- utive hours. This quantity is used because the composi- tion differs when voided at different periods. What is the reaction of urine? What conditions in- fluence this? The reaction of "24. hour " urine, under normal con- ditions, is slightly acid, due not to free acids, but to acid salts as NaH2P04. 1. The reaction depends essentially upon the compo- sition of the food. Animal food yields an abundance of acid radicals, while vegetable food contains organic acids, readily converted into basic bodies. 2. The amount of acid radicals withdrawn from the blood for specific purposes as gastric digestion. What is meant by the alkaline tide of the urine? After taking food, when a large amount of gastric juice containing HCl is being secreted, the alkalinity of the blood is temporarily increased. Synchronous with this, there is a corresponding increased alkalinity of the urine, which is called the '' alkaline tide." The urine becomes turbid due to the precipitation of basic Ca and Mg phosphates. Why is the specific gravity of urine important? As what are the solids determined? The specific gravity is an indication of the amount of solids. This amount cannot be reckoned by ordinary methods of analysis due to the fact that urea decomposes liberating NH3. The determination of constituents is in grams per 24 hours and not percentage, as the amount of liquid is very variable. 94 PHYSIOLOGICAL CHEMISTRY. What is the specific gravity of urine? How is the amount of total solids determined from this? The average specific gravity is 1020. It may vary considerably. The total solids are determined by Christison's formula. Multiply the last two figures of the specific gravity by the figure 2.34. This gives the grams per litre of solids. What are the phosphates in the urine? What salts are precipitated when the urine is made alkaline ? There are four phosphates. 1. The alkaline phosphates of Na and K which occur in largest amounts. 2. Soluble earthy phosphates of Ca and Mg. 3. Triple phosphate (magnesium ammonium phos- phate) which crystallizes in regular forms in the shape of coffin-lids and which proves that urea has decomposed. 4. Stellar phosphate. The latter two are abnormal constituents. The earthy phosphates are completely precipitated in alkaline urine. What is urea? Urea is the most important nitrogenous end product of proteid metabolism. About nine-tenths of the ■ N in proteid food passes off in this form. Though a base, forming salts with such acids as nitric and acetic, it occurs in the urine in an absolutely free condition. How is urea formed in the body? Practically all the N of proteids is converted into amino acids before regeneration occurs. In digestion, these amino acids are taken into the villi and, appearing in the blood as serum proteid, are reconverted into tissue pro- teids. Later, these are broken down into amino-acids, creatinin, etc., and finally into NH3, CO2, and HgO. The NH3 is poisonous and immediately combines with 96 PHYSIOLOGICAL CHEMISTRY. the CO2 and HgO forming (NH4)2C03. This ammonium carbonate is dehydrated into less poisonous ammonium carbamate. This in turn, by the expulsion of a molecule of water, yields urea, thus : /ONH, \ONH4 -H^O = /ONH, \NH2 Am. Carbonate. Am. Carbamate, /ONH^ = C < \NH2 -H2O = Am. Carbamate. Urea. This transformation takes place in the liver. How may urea be prepared? To a litre of urine, add 150 c.c. of baryta mixture (one part barium nitrate to two parts barium hydroxide). This precipitates the phosphates and sulphates. Filter. The filtrate contains all but the inorganic substances. Pour in a small beaker of alcohol. Stir thoroughly and filter. The filtrate contains the urea, creatinin and pig- ments. Evaporate on a water-bath to small bulk. Upon cooling, crystals of urea will separate out. What is a good qualitative test for urea? From concentrated solutions, urea combines with such acids as nitric and oxalic, forming crystals of charac- teristic shape. The test with nitric is the best. How may the amount of urea in urine be estimated? It may be determined in terms of the N which it liberates. Hypohromite Method. — This test depends upon the fact that urea is decomposed by an alkaline solution of sodium hypobromite, yielding N, HgO, and COg, thus : CO < -1- 3Na OBr = N, + CO^ -f 2H2O + 3NaBr. \NH, CO2 combines with the NaOH in the mixture. Each cc. of N ^ .00282 gr. urea. ^lifu to. i^^^J^ ^-^ CriOxxuS^.ttHxi*' /»■ C = e orvH-