Cornell University Library 
 S 585.G46 
 
 Address to the chemical section of the B 
 
 3 1924 000 286 728 
 
Cornell University 
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 The original of tiiis book is in 
 tine Cornell University Library. 
 
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 http://www.archive.org/details/cu31924000286728 
 
SWANSEA, 188 0. 
 
 ADDRESS 
 
 TO THE 
 
 CHEMICAL SECTION 
 
 OP TEE 
 
 BEITISH ASSOCIATION. 
 
 BY 
 
 J. H. GILBERT, PJi. D., V.B.S., V.P.G.S., F.L.8., 
 
 PRESIDENT OP THE SECTION. 
 
 Some of my predecessors in this Chair, whose duties as teachers of chemistry lead 
 them to traverse a wide range of the subject every year, have appropriately and 
 usefully presented to the Section a riswmS of the then recent progress in the mani- 
 fold branches of the science which have now such far-reaching ramifications. Such 
 a course has, however, come to be of much less importance and interest of late years, 
 since the systematic publication by the Chemical Society of abstracts of chemical 
 papers in home and foreign journals as soon as possible after their appearance. 
 Some, on the other hand, have confined attention to a department with which 
 their own enquiries have more specially connected them. And, when the Council 
 of the Association request a specialist like myself to undertake the Presidency of 
 the Section, it is to be supposed they take it for granted that he wiU select for his 
 opening address some branch of the subject with which he is known to be mainly 
 associated. 
 
 But it seems to me that there is a special reason why I should bring the subject 
 of Agiicultural Chemistry before you on the present occasion. Not only is the 
 application of chemistry to agriculture included in the title of this Section ; but in 
 1837 the Committee of the Section requested the late Baron Liebig to prepare a 
 report upon the then condition of Organic Chemistry, and it is now exactly forty 
 years since Liebig presented to the British Association the first part of his report, 
 which was entitled 0)-ganie Chemistry in its Applications to Agriculture and Physi- 
 ology ; and the second part was presented two years later, in 1842, iinder the title 
 oi Animal Chemistry, or Organic Chemistry in its application to Physiology and 
 <, Pathology. Yet, so far as I am aware, no President of the Section has, from that 
 J time to the present, taken as the subject of his address the Application of Chemistry 
 to Agriculture. 
 
 Appropriate as, for these reasons, it would seem that I, who have devoted a very 
 Jarge portion of the interval since the publication of Liebig's works, above referred 
 Vl SEC. B. C 
 
to, to agricultural enquiriea, should occupy the short time that can he devoted to 
 such a purpose in attempting to note progress on that important subject, it will he 
 readily imderstood that it would be quite impossible to condense into the limits of 
 an hour's discourse anything approaching to an adequate account, either of the 
 progress made during the last forty years, or of the existing condition of agricultural 
 chemistry. 
 
 For what is agricultural chemistry ? It is the chemistry of the atmosphere ; 
 the chemistry of the soil ; the chemistry of vegetation ; and the chemistry of 
 animal life and growth. And but a very imperfect indication of the amount of 
 labour which has been devoted of recent years to the investigation of these various 
 branches of what might at first sight seem a limited subject will sufBce to convince 
 you how hopeless a task it would be to seek to do more than direct attention to a 
 few points of special interest. Indeed, devoting to the purpose such leisure as I have 
 been able to command, the more I have attempted to become acquainted with the 
 vast literature which has been accumulated on the subject, the more difficulty have 
 I felt in making a selection of illustrations which should not convey an idea of the 
 limits, rather than of the extent, of the labour which has been expended, and of the 
 results which have been attained, in agricultural research. 
 
 The works of Liebig to which I have referred have, as you all know, been the 
 subject of a very great deal of controversy. Agricultural chemists, vegetable 
 physiologists, and animal physiologists have each vehemently opposed some of the 
 conclusions of the author, bearing upon their respective branches. But if the part 
 which has fallen to my own lot in these discussions qualifies me at all to speak for 
 others as well as myself, I would say that those who, having themselves carefully 
 investigated the points in question, have the most prominently dissented from any 
 special views put forward in those works, will — whether they be agricultural 
 chemists, vegetable physiologists, or animal physiologists — be the first to admit 
 how vast has been the stimulus, and how important has been the direction, given 
 to research in their own department, by the masterly review of then existing 
 knowledge, and the bold, and frequently sagacious, generalisations of one of the 
 most remarkable men of his time ! 
 
 Confining attention to researches bearing upon agriculture, it will be well, 
 before attempting to indicate either the position established by Liebig's first works, 
 or the direction of the progress since made, to refer very briefly to the early history 
 of the subject. 
 
 _ From what we now know of the composition and of the sources of the con- 
 stituents of plants, it is obvious that a knowledge of the composition of the atmo- 
 sphere and of water was essential to any true conception of the main features 
 of the vegetative process; and it is of interest to observe that it was almost simul- 
 taneously with the establishment, towards the end of the last century, of definite 
 knowledge as to the composition of the air and of water, that their mutual rela^ 
 tions with vegetation were first pointed out. To the collective labours of Black, 
 Scheele, Pnestley, Lavoisier, Cavendish, and Watt, we owe the knowledge that 
 common air consists chiefly of nitrogen and oxygen, with a little carbonic acid ; 
 that carbonic acid is composed of carbon and oxygen ; and that water is composed 
 of hydrogen and oxygen ; whilst Priestley and Ingenhousz, Sennebier and Wood- 
 house, investigated the mutual relations of these bodies and vegetable growth. 
 Priestley observed that plants possessed the faculty of purifying air vitiated by 
 pomhustion or by the respiration of animals ; and, he having discovered oxygen, 
 rt was found that the gaseous bubbles which Bonnet had shown to be emitted 
 trom the surface of leaves plunged in water consisted principaUy of that gas. In- 
 genhousz demonstrated that the action of light was essential to the development of 
 these phenomena; and Sennebier proved that the oxygen emitted resulted from 
 the decomposition of the carbonic acid taken up. 
 
 So far, however, attention seems to have been directed more prominently to 
 the question of the influence of plants upon the media with which they were sur- 
 rounded, than to that of the influence of those media in contributing to the in- 
 creased substance _ot the plants themselves. Towards the end of the last century, 
 and m the beginning of the present one, De Saussure followed up these enquiriea ; 
 
and in his work entitled, Reeherohes Chimiques sur la V^gUntion, published in 1804 
 he may be said to have indicated, if not indeed established, some of the most 
 important facts with which we are yet acquainted regarding the sources of the 
 constituents stored up by the growing plant. De Saussure illustrated experi- 
 mentally, and even to some extent quantitatively, the fact that in sun-light plants 
 increase in carbon, hydrogen, and oxygen, at the expense of carbonic acid and of 
 water ; and in the case of his main experiment on the pointy he found the increase 
 in carbon, and in the elements of water, to be very closely in the proportion in 
 which these are known to exist in the carbohydrates. He further maintained the 
 essentialness of the mineral or ash constituents of plants ; he pointed out that th«y 
 must be derived from the soil ; and he called attention to the probability that the 
 incombustible constituents so derived by plants from the soil were the source of 
 those found in the animals fed upon them. 
 
 With regard to the nitrogen which plants had already been shown to contain, 
 Priestley and Ingenhousz thought their experiments indicated that they absorbed 
 free nitrogen from the atmosphere ; but Sennebier and Woodhouse arrived at an 
 opposite conclusion. De Saussure, again, thought that his experiments showed 
 rather an evolution of nitrogen at the expense of the substance of the plant than 
 any assimilation of it from gaseous media. He further concluded that the source 
 of the nitrogen of plants was more probably the nitrogenous compounds in the soil, 
 and the small amount of ammonia which he demonstrated to exist in the atmo- 
 sphere. 
 
 Upon the whole, De Saussure concluded that air and water conti-ibuted a much 
 larger proportion of the dry substance of plants than did the soils in which they 
 grew. In his view a fertile soil was one which yielded liberally to the plant 
 nitrogenous compounds, and the incombustible or mineral constituents ; whilst the 
 carbon, hydrogen, and oxygen, of which the greater proportion of the dry substance 
 of the plant was made up, were at least mainly derived from the air and water. 
 
 Perhaps I ought not to omit to mention here that, each year for ten successive 
 years, from 1802 to 1812, Sir Humphry Davy delivered a course of lectures on the 
 Elements of Agricultwcd Chemistry, which were first published in 1813, were 
 finally revised by the author for the Fom'th Edition in 1827, but have gone through 
 several editions since. In those Ijectures, Sir Humphry Davy passed in review 
 and correlated the then existing knowledge, both practical and scientific, bearing 
 upon agricultm'e. He treated of the influences of heat and light ; of the organisa- 
 tion of plants ; of the difference, and the change, in the chemical composition of 
 their different parts ; of the sources, composition, and treatment of soils ; of the 
 composition of the atmosphere, and its influence on vegetation ; of the composition 
 and the action of manures ; of fermentation and putrefaction ; and finally of the 
 principles involved in various recognised agricultural practices. 
 
 With the exception of these discourses of Sir Humphry Davy, the subject 
 seems to have received comparatively little attention, nor was any important addi- 
 tion made to our knowledge in regard to it, during the period of about thirty years, 
 from the date of the appearance of De Saussure's work in 1804 to that of the com- 
 mencement of Boussingault's investigations.' 
 
 About 1834, Boussingault became, by marriage, joint proprietor with his 
 brother-in-law of the estate of Bechelbronn, in Alsace. His brother-in-law, M. 
 Lebel, was both a chemical manufacturer and an intelligent practical farmer, 
 accustomed to use the balance for the weighing of manures, crops, and cattle. 
 Boussingault seems to have applied himself at once to chemico-agrioultural 
 research ; and it was under these conditions of the association of ' practice with 
 science ' that the first laboratory on a farm was established. 
 
 From this time forward, Boussingault generally spent about half the year in 
 Paris, and the other half in Alsace ; and he has continued his scientific labours, 
 sometimes in the city, and sometimes in the country, up to the present time. His 
 
 ' Some reference should have been made in the text to the labours and writings 
 of Dr. Carl Sprengel, late Professor of Agriculture at Brunswick, who made i^umeroiis 
 analyses of agricultural materials, and published numerous papers in connection with 
 Agricultural Chemistry, during a series of years, commencing about 1826. 
 
 c2 
 
first important contribution to agricultural chemistry wa3 made in 1836, wlien M 
 published a paper on the amount of nitrogen in different foods, and on the equiva- 
 lence of the foods, founded on the amounts of nitrogen they contained ; and he 
 compared the results so arrived at with the estimates of others founded on actual 
 experience. Although his conclusions on the subject have doubtless undergone 
 modification since that time, the work itself marked a great advance on previously 
 existing knowledge, and modes of viewing the question. 
 
 In 1837, Boussingault published papers— on the amount of gluten in different 
 kinds of wheat ; on the influence of the clearing of forests on the diminution of the 
 flow of rivers ; and on the meteorological influences affecting the culture of the vine, 
 lu 1838 he published the results of an elaborate research on the principles under- 
 lying the value of a rotation of crops. He determined by analysis the composition, 
 both organic and inorganic, of the manures appUed to the land, and of _ the crops 
 harvested. In his treatment of the subject he evinced a clear perceptionof the 
 most important problems involved in such an enquiry ; some of which, with the 
 united labours of himself and many other workers, have scarcely yet received an 
 undisputed solution. 
 
 Thus, in the same year (1838), he published the results of an investigation on 
 the question whether plants assimilate the free or uncombined nitrogen of the 
 atmosphere; and although the analytical methods of the day were inadequate to 
 the decisive settlement of the point, his conclusions were in the main those which 
 much subsequent work of his own, and much of others also, has served to confirm. 
 
 As a further element of the question of the chemical statistics of a rotation of 
 crops, Boussingault determined the amount and composition of the residues of 
 various crops ; also the amount of constituents consumed in the food of a cow and 
 of a horse respectively, and yielded in the milk and excretions of the cow, and in 
 the excretions of the horse. Here, again, the exigencies of the investigation he 
 undertook were beyond the reach of the known methods of the time. Indeed, rude 
 as the art of agriculture is generally considered to be, the scientific elucidation of 
 its practices requires the most refined, and very varied, methods of research ; and 
 a characteristic of the work of Boussingault may be said to be, that he has fre- 
 quently had to devise methods suitable to his purpose, before he could grapple with 
 the problems before him. 
 
 In 1839, chiefiy in recognition of his important contributions to agricultural 
 chemistry, Boussingault was elected a member of the Institute ; and in 1878, 
 thirty-nine years later, the Council of the Koyal Society awarded to him the 
 Copley Medal, the highest honour at their disposal, for his numerous and varied 
 contributions to science, but especially for those relating to agriculture. 
 
 The foregoing brief historical sketch is sufficient to indicate, though but in broad 
 outline, the range of existing knowledge on the subject of agricultural chemistry 
 prior to the appearance of Liebig's memorable work m 1840. It will be seen that 
 some very important and indeed fundamental facts had already been established in 
 regard to vegetation, and that Boussingault had not only extended enquiry on that 
 subject, but he had brought his own and previous results to bear upon the elucida- 
 tion of long-recognised agricultural practices. There can be no doubt that the data 
 supplied by his researches contributed important elements to the basis of established 
 facts upon which Liebig founded his brilliant generalisations. Accordingly, in 
 1841, Dumas and Boussingault published, jointly, an essay which afterwards 
 appeared in English under the title of The Chemical and Physiological Balance of 
 Organic Nature ; and, in 1843, Boussingault published a larger work, which 
 embodied the results of many of his own previous original investigations. 
 
 But there can be no doubt that the appearance of Liebig's two works, which 
 were contributions made in answer to a request submitted to him by the committee 
 of this Section of the British Association, constituted a very maried epoch in the 
 history of the progress of agricultural chemistry. In the treatment of his subject 
 he not only called to his aid the previously existing knowledge directly bearing 
 upon it, tut he also turned to good account the more recent triumphs of organic 
 chemistry, many of which had been won in his own laboratory. Further, a marked 
 feature of his expositions was the adoption of what may be called the statistical 
 
method — I use the word statistical rather than quantitative, as the latter expression 
 lias its own technical meaning among chemists, which is not precisely what I wish 
 to convey. 
 
 It seems that, notwithstanding the conclusive evidence afforded by the direct 
 experiments of De Saussure and his predecessors, vegetable physiologists continued 
 to hold the view that the humus of the soil was the source of the carbon of vege- 
 tation. Not only did Liebig p-ive full weight to the evidence of the experiments of 
 De Saussure and other's, and illustrate the possible or probable transformations 
 within the plant by facts already established in organic chemistry, but he demon- 
 strated the utter impossibility of humus supplying the amount of carbon assimilated 
 over a given area. He pointed out that humus itself was the product of previous 
 vegetable growth, and that it could not therefore be an original source of carbon ; 
 and that, from the degree of its insolubility, either in pure water or in water con- 
 taining alhaline or earthy bases, only a small portion of the carbon assimilated by 
 plants could be derived from the amount of humus that could possibly enter the 
 plant in solution. He maintained that, so far as humus was beneficial to vegeta- 
 tion at all, it was only by its oxidation, and a consequent supply of carbonic acid 
 within the soil ; a source which he considered only of importance in the early stages 
 of the life of a plant, and before it had developed and exposed a sufficient amount 
 of green surface to the atmosphere to render it independent of soil supplies of 
 carbonic acid. 
 
 With regard to the hydrogen of plants, at any rate that portion of it contained 
 in their non-nitrogenous products, he maintained that its source must be water ; 
 and that the som'ce of the oxygen was either that contained in carbonic acid or 
 that in water. 
 
 With regard to the nitrogen of vegetation, both from the known characters of 
 free nitrogen, and as he considered a legitimate deduction from direct experiments, 
 he argued that plants did not take up free or uncombined nitrogen, either from the 
 atmosphere, or dissolved in water and so absorbed by the roots. The source of the 
 nitrogen of vegetation was, he maintained, ammonia ; the product of the putrefaction 
 of one generation of plants and animals affording a supply for its successors. He 
 pointed out that, in the case of a farm receiving nothing from external sources, and 
 selling off certain products, the amount of nitrogen in the manure derived by the con- 
 sumption of some of the vegetable produce on the farm itself, together with that due 
 to the refuse of the crops, must always be less than was contained in the crops 
 grown ; and he concluded that though the quantity so returned to the land was 
 important, a main source of the nitrogen assimilated over a given area was that 
 brought down from the atmosphere in rain. 
 
 There can be no doubt that, owing to the limited and defective experimental 
 evidence then at command on the point, Liebig at that time (as he has since) 
 greatly over-estimated the amount of ammonia available to vegetation from that 
 source. In Boussingault's ' reclamation ' already referred to, he gave much more 
 prominence to the importance of the nitrogen of manures. In Liebig's next edition 
 (in 1843) he combated the notion of the relative importance of the nitrogen of 
 manures ; maintained, in opposition to the view put forward in his former edition 
 that the atmosphere afforded a sufficient supply of nitrogen for cultivated as well as 
 for uncultivated plants ; that the supply was sufficient for the cereals as well as for 
 leguminous plants ; that it was not necessary to supply nitrogen to the former ; 
 and he insisted very much more strongly than formerly on the relative importance 
 of the supply of the incombustible, or, as he designated them, the ' inorganic ' or 
 ' mineral,' constituents. 
 
 As to the incombustible or mineral constituents themselves, Liebig adduced 
 many illustrations in proof of their essentialness. He called attention to the 
 variation in the composition of the ash of plants grown on different soils ; and he 
 assumed a greater degree of mutual replaceability of one base by another, or of one 
 acid by another, than could be now admitted. lie traced the diflerence in the 
 mineral composition of different soils to that of the rocks which had been their 
 source ; and he seems to have been led by the consideration of the gradual action 
 of ' weatheririf/! in rendering available the otherwise locked-lip stores, to attribute^ 
 
the benefits of fallow exclusively to the increased supply of the incomkistiUe 
 constituents which would, by its agency, be brought into a condition in which they 
 could be taken up by plants. . , 
 
 The benefits of an alternation of crops Liebig considered to be m part explamea 
 by the influence of the excreted matters from one description of crop upon the 
 growth of another. He did not attach weight to the assumption that such matters 
 woidd be directly injurious to the same description of crop ; but he supposed rather 
 that the matters excreted were those which the plant did not need, and would 
 therefore be of no avail to the same description of plant, but would be oi use to 
 another. He, however, attributed much of the benefits of a rotation to dilierent 
 mineral constituents being required from the soil by the respective crops. 
 
 Treating of manure, he laid the greatest stress on the return by it of the potass 
 and the phosphates removed by the crops. But he also insisted on the importance 
 of the nitrogen, especially that in the liquid excretions of animals, and condemned 
 the methods of treatment of animal manures by which the ammonia was allowed 
 to be lost by evaporation. It is curious and significant, however, that some of the 
 passages in his first edition, in which he the most forcibly urges the value of the 
 nitrogen of animal manures, are omitted in the third and fourth editions. 
 
 The discussion of the processes of fermentation, decay, and putrefaction, and 
 that of poisons, contagions, and miasms, constituted a remarkable and important 
 part of Liebig's first report. It was the portion relating to poisons, contagions, 
 and miasms, that he presented to this Section as an instalment, at the meeting of 
 the Association held at Glasgow in 1840. It was in the chapters relating to the 
 several subjects here enumerated that he developed so prominently his views on 
 the influence of contact in inducing chemical changes. He cited many knovi^n 
 transformations, other than those coming under either of the heads in question, in 
 illustration of his subject ; and he discussed with great clearness the dilierent con- 
 ditions occurring, and the different results obtained, in various processes — such as 
 the diflerent modes of fermenting beer, the fermentation of wine from difierent 
 kinds of grapes, the production of acetic acid, &o. As is well known, he claimed 
 a purely chemical explanation for the phenomena involved in fermentation. He 
 further maintained that the action of contagions was precisely similar. In his latest 
 writings on Ibe subject (in 1870), he admits some change of view ; but it is by no 
 means easy to decide exactly how much, or how little of modification he would wish 
 to imply, 
 
 Liebig's second report, presented at the meeting of this Association in 1842, 
 and published under the title of Animal Chemistry, or Organic Cliemistry in its 
 applications toPhynology and Pathology, perhaps excited even more attention than his 
 first, and, probably from the' manner as much as from the matter, aroused a great 
 deal of controversy, especially among physiologists and physicians. Liebig was 
 severe upon what he considered to be a too exclusive attention to morphological 
 characters in physiological research, and at any rate too little attention to chemical 
 phenomena, and, so far as these were investigated, an inadequate treatment of the 
 subject according to strictly quantitative methods. 
 
 He combated the view that nervous action, as such, could be a source of any 
 of the heat of the body ; and he adduced numerous illustrations and calculations in 
 support of the view that the combustion of carbon and hydrogen in the system 
 was suiEcient to account for, and was the only source of, animal heat. 
 
 He compared and contrasted the general composition of plants and animals. 
 In accordance with Mulder, he pointed out that whilst plants formed the nitro- 
 genous bodies which they contain from carbonic acid, water, and ammonia, animals 
 did not produce them, but received them ready-formed in their vegetable food ; 
 that, in fact, the animal begins only where the plant ends. But, going beyond 
 Mulder, and beyond what had then, or has since, been established, he maintained the 
 identity in composition of the admittedly analogous nitrogenous compounds in plants 
 and in the blood of animals. 
 
 Omitting the fat which the carnivora might receive in the animals they con- 
 sumed, he stated the characteristic difference between the food of carnivora and 
 kerbivora to be, that the former obtained the main proportioa of their respiratory 
 
material from the waste of tissue ; whilst the latter ohtained a large amount from 
 starch, sugar, &c. These difterent conditions of life accounted for the comparative 
 leanness of carnivora and fatness of herbivora. 
 
 He maintained that the vegetable food consumed by herbivora did not contain 
 anything like the amount of fat which they stored up in their bodies ; and he 
 showed how nearly the composition of fat was obtained by the simple elimination 
 of so much oxygen, or of oxygen and a little carbonic acid, from the various carbo- 
 hydrates. Much less oxygen would be required to be eliminated from a quantity 
 of fibrine, &c., containing a given amount of carbon, than from a quantity of carbo- 
 hydrates containing an equal amount of carbon. The formation of fatty matter in 
 plants was of the same kind ; it was the result of a secondary action, starch being 
 first formed from carbonic acid and water. 
 
 He concluded from the facts adduced that the food of man might be divided 
 into the nitrogenised and the Tion-nitrogenised elementB. The former were capable of 
 conversion into blood, the latter incapable of such transformation. The lormer might 
 be called the plastic elements of nutrition, the latter elements of respiration. From 
 the plastic elements, the membranes and cellular tissue, the nerves and brain, carti- 
 lage, and the organic part of bones, could be formed ; but the plastic substance 
 must be received ready-made. "Whilst gelatine or chondrine was derived from 
 fibrine or albumen, fibrine or albumen could not be reproduced from gelatine or 
 chondrine. The gelatinous tissues suffer progressive alteration under the influence 
 of oxygen, and the materials for their re-formation must be restored from the blood. 
 It might, however, be a question whether gelatine taken in food might not again 
 be converted into cellular tissue, membrane, and cartilage, in the body. 
 
 At that time, adopting and attaching great importance to Mulder's views in 
 regard to proteine, he says: — 'All the organic nitrogenised constituents of the 
 body, how different soever they may be in composition, are derived from proteine. 
 They are formed from it by the addition or subtraction of the' elements of water 
 or of oxygen, and by resolution into two or more compounds.' 
 
 He seeks to trace the changes occurring in the conversion of the constituents of 
 food into blood, of those of blood into the various tissues, and of these into the 
 secretions and excretions. 
 
 He states that the process of chymification takes place in virtue of a purely 
 chemical action, exactly similar to those processes of decomposition or translbrma- 
 fion which are known as putrefaction, fermentation, or decay. Thus, the clear 
 gastric juice contains a substance in a state of transformation, by the contact of 
 which with the insoluble constituents of the food they are rendered soluble, no 
 other element taking any share in the action excepting oxygen and the elements of 
 water. All substances which can arrest the phenomena of fermentation and putre- 
 faction in liquids, also arrest digestion when taken into the stomach. Putrefying 
 blood, white of egg, flesh, and cheese produce the same effects in a solution of 
 sugar as yeast or ferment ; the explanation being, that ferment, or yeast, is nothing 
 but vegetable fibrine, albumen, or caseine, in a state of decomposition. 
 
 Referring to the derivation of the animal tissues, he says they all contain, for a 
 given amount of carbon, more oxygen than the nitrogenous constituents of blood. 
 In hair and gelatinous membrane there is also an excess of nitrogen and hydrogen, 
 and in the proportions to form ammonia. We may suppose an addition of these 
 elements, or a subtraction of carbon, the amount of nitrogen remaining the same. 
 The gelatinous substance is not a compound of proteine ; it contains no sulphur, no 
 phosphorus ; and it contains more nitrogen, or less carbon, than proteine. 
 
 He next, as he says, attempts to develop analytically the principal metamor- 
 phoses which occur in the animal body. He adds that the results have surprised 
 himself no less than they will others, and have excited in his own mind the same 
 doubts as others will conceive. He nevertheless gives them, because he is con- 
 vinced that the method by which they have been obtained is the only one by which 
 we can hope to acquire an insight into the nature of organic processes. 
 
 Referring to the animal secretions, he argues that they must contain the pro- 
 ducts of the metamorphosis of the tissues. He says a starving^ man with severe 
 exertion secretes more urea than the most highly fed individual in a state of rest ; 
 
and he combats the idea that the nitrogen of the food can pass into urea -without 
 having previously become part of an organised tissue. 
 
 Having shown the chemical relations of bile and urine to the proteine bodies, 
 he illustrates, by formulae, the connection between allantoine and the constituents 
 of the urine of animals that respire. He insists that in the herbivora the carbo- 
 hydrates must take part in the formation of bile; and he calculatesthe number 
 of equivalents of proteine, starch, oxygen, and water, which would yield a given 
 number of equivalents of urea, choleic acid, ammonia, and carbonic acid. The non- 
 nitrogenous constituents in the food of the herbivora retard the metamorphosis of 
 the nitrogenous bodies, rendering this less rapid than in the carnivora. It may be 
 said that proteine, stdrch, and oxygen give the secretions and excretions — carbonic 
 acid by the lungs, urea and carbonate of ammonia by the kidneys, choleic acid by 
 the liver. It is the study of the phenomena which accompany the metamorphoses 
 of the food in the organism, the discovery of the share which the atmosphere and 
 the elements of water take in these changes, by which we shall learn the conditions 
 necessary for the production of a secretion or of an organised part. 
 
 He traces the possible formation of taurine from caifeine or asparagine by their 
 assumption of oxygen and of the elements of water. And from the composition 
 of the vegetable alkaloids he suggests the possibility of their taking a share in the 
 formation of new, or the transformation of existing, brain and nervous matter. 
 
 Finally, iu reference to these various illustrations and considerations, he saye, 
 however hypothetical they may appear, they deserve attention in so far as they 
 point out the way which chemistry must pursue if she would really be of service 
 to physiology and pathology. Chemistry, he says, relates to the conversion of food 
 into the various tissues and secretions, and to their subsequent metamorphosis into 
 lifeless compounds. 
 
 After this lapse of time, it will certainly be granted that, quite irrespectively of 
 the admissibility or otherwise of the particular illustrations adduced, or of the 
 truth or error of any of the conclusions drawn — and some at least are so true that 
 they seem to us now all but truisms, and you may be disposed to ask me why I 
 should tell you over again a story so often told before — there is no doubt that 
 Liebig's manner of treating the subject did exert an immense influence, by stimu- 
 lating investigation, by fixing attention on the points to be investigated, and on 
 the methods that must be followed, and thus, by leading to the establishment or 
 the correction of any special views he put forward, and to a vast extension of our 
 knowledge on the complicated questions involved. 
 
 In the third part of Liebig's second volume he treats of the phenomena of 
 motion in the animal organism. It is to his views in regard to one aspect only of 
 this very wide and very complicated subject that I propose to call your attention 
 here, as it is chiefly in so far as that aspect is concerned that the question is of 
 interest from the point of view of the agricultural chemist. He says : — 
 
 ' "We observe in animals that the conversion of food into blood, and the contact 
 of the blood with the living tissues, are determined by a mechanical force, whose 
 manifestation proceeds from distinct organs, and is effected by a distinct system of 
 organs, possessing the property of communicating and extending the motion which 
 they receive. We find the power of the animal to change its place and to produce 
 mechanical efieots by means of its limbs dependent on a second similar system of 
 organs or apparatus.' 
 
 He points out that the motion of the animal fluids proceeds from distinct 
 organs (as, for example, that of the blood from the heart), which do not generate 
 the force in themselves, but receive itfrom other parts by means of the nerves ; the 
 limbs also receive their moving force in the same way. He adds : ' Where nerves 
 are not found, motion does not occur.' Again: — 
 
 ' As an immediate effect of the manifestation of mechanical force, we see that a 
 part of the muscular substance loses its vital properties, its character of life ; that 
 this portion separates from the living part, and loses its capacity of growth and its 
 power of resistance. We find that this change of properties is accompanied by 
 the entrance of a foreign body (oxygen) into the composition of the muscular 
 fibre. . . ; and all experience proves that this conversion of living muscular fibre into 
 
cotapcfunda destitute of vitality ia accelerated Or retarded according' to the amount' 
 of force employed to produce motion.' fie adds that a rapid transformation of 
 muscular fibre determines a greater amount of mechanical force, and that con- 
 versely a greater amount of mechanical motion determines a more rapid change of 
 matter. 
 
 ' The change of matter, the manifestation of niechanical force, and the absorp- 
 tion of oxygen, are, in the animal body, so closely connected with each other that 
 we may consider the amount of motion and the quantity of living tissue transformed 
 as proportional to the quantity of oxygen inspired and consiuned in a given time 
 by the animal.' Again: — 
 
 ' The production of heat and the change of matter are closely related to each 
 other ; but although heat can be produced in the body without any change of 
 matter in living tissues, yet the change of matter cannot be supposed to take place 
 without the co-operation of oxygen.' 
 
 Further, on the same point : — ' The sum of force available for mechanical pur- 
 poses must be equal to the sum of the vital forces of all tissues adapted to the 
 change of matter. If, in equal times, unequal quantities of oxygen are consumed, 
 the result is obvious ih an 'uneqlial amount of heat liberated, and of mechanical 
 force. When unequal amounts bi mechanical force are expended, this determines 
 the absorption of corrfesponding And uhequal quantities of oxygen.' 
 
 Then, more definitely still, referrin* to the changes which take place coincidently 
 with the exercise of fdrce, tad to the demands of the system for repair accordingly, 
 he says : — ... 
 
 ' The amount of aZotised food necessary to restore the equilibrium between waste 
 and supply is directly" proportional to' the amount of tissues metamorphosed. The 
 amount of living matter, which in the body loses the condition of life,, is, in equal 
 temperatures, directly proportional to the mechanical effects produced in a given 
 time. The amount of tissde mStamorphoSed in" a given time may be measured by 
 the quantity of nitrogen in the urine. The sum of the mechanical effects produced 
 in two individuals, in the shvae fempei'ature, is proportional to the amount of nitro- 
 gen in their urine, whether the mechanical force has been employed in the voluntarv 
 or involuntary motions, whether it has been consumed by the limbs, or by the heart 
 and other viscera.' 
 
 Thus, apparently influenced by the physiological considerations which have been 
 adduced, and notwithstanding in some passages he seemed to recognise a connection 
 between the total quantity of oxygon inspired and consumed and the quantity of 
 mechanical force developed, Liebig nevertheless very prominently insisted that the 
 amount of muscular tissue transformed — the amount of nitrogenous substance oxi- 
 dated — was the measure of the force generated. He accordingly distinctly draws 
 the conclusion that the requirement for the azotised constituents of food will be in- 
 creased in proportion to the increase in the amount of force expended. 
 
 It will be obvious that the question whether in the feeding of animals for the 
 exercise of mechanical force, that is, for their labour, the demands of the system 
 will be proportionally the greater for an increased supply of the nitrogenous or of 
 the non-nitrogenous constituents of food, is one of considerable interest and prac- 
 tical importance. To this point I shall have to refer further on. 
 
 So far, I have endeavoured to convey some idea of the state of knowledge on the 
 subject of the chemistry of agriculture prior to the appearance of Liebig's first two 
 works bearing upon it, and also briefly to summarise the views he then enunciated 
 in regard to some points of chief importance. Let us next try to ascertain some- 
 thing of the influence of his teaching. 
 
 Confining attention to agricultural research, it may be observed that in 1843 — 
 that is, very soon after the appearance of the works in question — the Royal Agri- 
 cultural Society of England first appointed a consulting chemist. At that date 
 Dr. Lyon Playfair was elected; in 1848, Professor Way ; and in 1858 Dr. Voelcker, 
 who continues to hold the office with much advantage to that union of 'Practixie 
 ivith Science ' which the Society by its motto recognises as so essential to progress. 
 Also in 1843 there was established the Ohemioo- Agricultural Society of Scotland, 
 which was, I believe, broken up, after it had existed between four and five years, 
 
 c 5 
 
10 
 
 because its able chemist, the late Professor Johnston, failed to find a remedy for the 
 potato disease. In 1845, the Chemico-Agricultural Society of Ulster was estab- 
 lished, and appointed as its chemist, Professor Hodges, who still ably performs 
 the duties of the ofiice. Lastly, the very numerous 'Agricultural Experiment^ 
 Stations ' which have been established, not only in Germany, but in most Conti- 
 nental States, owe their origin directly to the writings, the teachings, and the 
 influence of Liebig. The movement seems to have originated in Saxony, where 
 Stockhardt had already stimulated interest in the subject by his lectures and his 
 writings. After some correspondence, in 1860-1, between the late Dr. Orucius 
 and others on the one side, and the Government on the other, the first so-called 
 Agricultural Experimental Station was established at Mbchern, near Leipzig, in 
 1851-3. In 1877, the twenty-fifth anniversary of the foundation of that institu- 
 tion was celebrated at Leipzig, when an account (which has since been published) 
 was given of the number of stations then existing, of the number of chemists engaged, 
 and of the subjects which had been investigated. From that statistical statement 
 we learn that in 1877 the number of stations was : — 
 
 In the various German States 
 
 
 74 
 
 In Austria 
 
 
 . 16 
 
 In Italy 
 
 In Sweden . 
 
 
 
 
 . 10 
 
 7 
 
 In Denmark . 
 
 
 
 
 1 
 
 In Russia 
 
 
 
 
 3 
 
 In Belgium • 
 In Holland . 
 
 
 
 
 3 
 
 2 
 
 In France 
 
 
 
 
 2 
 
 In Switzerland 
 
 
 
 
 3 
 
 In Spain 
 
 
 
 
 1 
 
 Total 
 
 122 
 
 Besides these 122 stations on the Continent of Europe, the United States are 
 credited with 1, and Scotland also with 1. 
 
 Each of these stations is under the direction of a chemist, frequently with one 
 or more assistants. One special duty of most of them is what is called manure- 
 or seed-or feeding-stufi-control ; that is, to examine or analyse, and repoi-t upon 
 such substances in the market ; and it seems to have been found the interest of dealers 
 in these commodities to submit their proceedings to a certain degree of supervision 
 by the chemist of the station of their district. 
 
 But agricultural research has also been a characteristic feature of these institu- 
 tions. It is stated that the investigation of soils has been the prominent object at 
 16 of them; experiments with manures at 24; vegetable physiology at 28;- 
 animal physiology and feeding experiments at 20 ; vine culture and wine-making at 
 13 ; forest culture at 9 ; and milk-production at 11. Others, according to their 
 locality, have devoted special attention to fruit culture, olive culture, the cultivation 
 of moor, bog, and peat land, the production of silk, the manufacture of spirit and 
 other products. ' 
 
 Nor does this enumeration of the institutions established as the direct result of 
 Liebig's influence, and of the subjects investigated under their auspices, complete 
 the list either of the workers engaged, or of the work accomplished in agricultural 
 research. To say nothing of the labours of Boussingault, which commenced some 
 years prior to the appearance of Liebig's first work, and which are fortunately still 
 at the service of agriculture, important contributions have been made by the late 
 Professors Johnston and Anderson in Scotland, and in this country both by Mr Way 
 and Dr. Voelcker, each alike in his private capacity, and in fulfilment of his duties as 
 Chemist to the Royal Agricultural Society of England. Nor would it be fair to 
 Mr. Lawes (who commenced experimenting first with plants in pots, and afterwards 
 in the field, soon after entering into possession of his property in 1834, and with whom 
 I have myself been associated since 1843), were I to omit in this place any mention 
 of the investigations which have been so many years in progress at Rothamsted 
 
u 
 
 So much for the machinery ; but what of the results achieved by all this 
 activity jn the application of chemistry to agriculture ? 
 
 As I have already intimated, and as the foregoing brief statistical statement 
 ■will have convinced you must be the case, it will be utterly impossible to give, on 
 such an occasion as this, anything approaching to an adequate review of the 
 progress achieved. Indeed, I have to confess that the more I have looked at the 
 subject with the hope of treating it comprehensively, the more I have been impelled 
 to substitute a very limited plan for the much more extended scheme which I had 
 at first hoped to be able to till up. I propose then to confine attention to a few 
 special points, which have either some connection with one another, or to which 
 recent results or discussions lend some special interest. 
 
 First as to the sources and the assimilation of the carbon, the hydrogen, and the 
 oxygen of vegetation. From the point of view of the agricultural chemist, the 
 hydrogen and the oxygen may be left out of view. For, if the cultivator provide 
 to the plant the conditions for the accumulation of sufficient nitrogen and carbon, 
 he may leave it to take care of itself in the matter of hydrogen and oxygen. That 
 the hydrogen of the carbo-hydrates is exclusively obtained from water, is, to say the 
 least, probable ; and whether part of their oxygen is derived from carbonic acid, and 
 part from water, or the whole from either of these, wiU not affect his agricultural 
 practice. 
 
 With regard to the carbon, the whole tendency of subsequent observations is to 
 confirm the opinion put forward by De Saussure about the commencement of the 
 century, and so forcibly insisted upon by Liebig forty years later— that the greater 
 part, if not the whole of it, is derived from the carbonic acid of the atmosphere. 
 Indeed, direct experiments are not wanting — those of Moll, for example — from 
 which it has been concluded that plants do not even utilise the carbonic acid which 
 they may take up from the soil by their roots. Plowever this may be, we may 
 safely conclude that practically the whole of the carbon -which it is the object of 
 the cultivator to force the plants he grows to take up is derived from the atmo- 
 sphere, in which it exists in such extremely small proportion, but nevertheless large 
 actual, and constantly renewed amount. 
 
 Judging from the more recent researches on the point, it would seem probable 
 that the estimate of one part of carbon, as carbonic acid, in 10,000 of air, is more 
 probably too high than too low as an estimate of the average quantity in the 
 ambient atmosphere of our globe. And, although this would correspond to several 
 times more in the column of air resting over an acre of land than the vegetation of 
 that area can annually take up, it represents an extremely small amount at any 
 one time in contact with the growing plants, and it could only suffice on the suppo- 
 sition of a very rapid renewal, accomplished as the result, on the one hand of a con- 
 stant return of carbonic acid to the atmosphere by combustion and the respiration 
 of animals, and on the other of a constant interchange and equalisation among the 
 constituents of the atmosphere. 
 
 It will convey a more definite idea of what is accomplished by vegetation in the 
 assimilation of carbon from the atmosphere if I give, in round numbers, the results 
 of some direct experiments made at Eothamsted, instead of making general state- 
 ments merely. 
 
 In a field which has now grown wheat for thirty-seven years in succession, there 
 are some plots to which not an ounce of carbon has been returned during the whole 
 of that period. Yet, with purely mineral manure, an average of about 1,000 pounds 
 of carbon is annually removed from the land ; and where a given amount of nitro- 
 genous manure is employed with the mineral manure, an average of about 1500 pounds 
 per acre per annum more is obtained ; in all an average of about 2,500 pounds of 
 carbon annually assimilated over an acre of land without any return of carbonaceous 
 manure to it. 
 
 In a field in which barley has been grown for twenty-nine years in succession, 
 quite accordant results have been obtained. There, smaller amounts of nitrogenous 
 manure have been employed with the mineral manure than in the experiments with 
 wheat above cited ; but the increase in the assimilation of carbon for a given amount 
 of nitrogen supplied in the manure is greater in the case of the barley than of the 
 wheat. 
 
12 
 
 "With sugar-beet, again, larger amounts of carbon have been annually accumu- 
 lated without the supply of any to the soil, but under the influence of a liberal 
 Jjrovision of both nitrogenous and mineral manure, than by either wheat or barley. 
 Lastly, with grass, still larger amounts of carbon have been annually accumu- 
 lated, without any supply of it by manure. 
 
 Many experim"ents have been made, in Germany and elsewhere, to determine the 
 amount of the different constituents taken up at different periods of the growth of 
 various plants. But we may refer to some made at Rothamsted long ago to illus- 
 trate the rapidity with which the carbon of our crops may be withdrawn from the 
 atmosphere. 
 
 In 1847, we carefully took.samples from a growing wheat crop at different stages 
 of its progress, commencing on June 21, and in these samples the dry matter, tlie 
 mineral matter, the nitrogen, &c., were determined. On each occasion the produce 
 of two separate eighths or sixteenths of an acre was cut and weighed, so that the 
 data were provided to calculate the amounts of the several constituents which had 
 been accumulated per acre at each period. The result was that, whilst during 
 little more than five weeks from June 21,' there was comparatively little increase 
 in the amount of nitrogen accumulated over a given area, more than half the total 
 carbon of the crop was accumulated during that period. 
 
 Numerous experiments of a somewhat similar kind, made in another season, 1856, 
 concurred in showing that, whilst the carbon of the crop was more than doubled 
 after the middle of June, its nitrogen increased in a much less degree over the same 
 period. 
 
 , Similar experiments were also made, in 1854 and in 1866, with beans. The 
 general result was that a smaller proportion of both the total nitrogen and the total 
 carbon was accumulated by the middle or end of June than in the case of the wheat ; 
 though the actual amount of nitrogen taken up by the beans was much greater, both 
 before and after that date. The nitrogen of this leguminous crop increased iu a 
 much greater proportion during the subsequent stages of growth than did that of 
 the gramineous crop ; but the carbon increased in a larger proportion still, three- 
 fourths or more of the total amount of it being accumulated after the middle of June. 
 I should say that determinations of carbon, made in samples of soil taken from 
 the wheat field at different periods during recent years, indicate some decline in the 
 percentage of carbon in the soils, but not such as to lead to the supposition that the 
 soils have contributed to the carbon of the crops. Besides the amount of carbon 
 annually removed, there will, of course, be a further accumulation in the stubble 
 and roots of the crops ; and the reduction in the total carbon of the soil, if such 
 have really taken place, would show that the annual oxidation within it is greater 
 than the annual gain by the residue of the crops. 
 
 Large as is the annual accumulation of carbon from the atmosphere over a given 
 area in the cases cited, it is obvious that the quantity must vary exceedingly with 
 variation of climatal conditions. It is, in fact, several times as great in the case of 
 tropical vegetation — that of the sugar-cane for example. And not only is the 
 greater part of the assimilation accomplished within a comparatively small portion 
 -of the year (varying of course according to the region), but the action is limited 
 to the hours of daylight, whilst during darkness there is rather loss than gain. 
 
 But it is remarkable that whilst the accumulation of carbon, the chief gain of 
 solid material, takes place under the influence of light, cell-division, cell-multipli- 
 cation, increase in the structure of the plant, in other words, what, as distinguished 
 from assimilation, vegetable physiologists designate as grmoth, takes place, at any 
 rate chiefly, during the night; and is accompanied, not with the taking up of 
 carbonic acid and the yielding up of oxygen, but with the taking up of oxygen and 
 the giving up of carbonic acid. This evolution of carbonic acid during darkness 
 must obviously be extremely small, compared with the converse action during day- 
 light, coincidentally with which practically the whole of the accumulation of solid 
 substance is accomplished. But, as the product of the night action is the same as 
 in the respiration of animals, this is distinguished by vegetable physiologists as the 
 respiration of plants. 
 
 I suppose I shall be considered a heretic if I venture to suggest that it seems in a 
 
13 
 
 sense inappropriate to apply tie term growth to tiat 'wMoli is associated with actual 
 loss of material, and tliat the term respiration should he applied to so secondary an 
 action as that as the result of which carhonic acid is given off from the plant. It 
 may, I think, he a question whether there is any advantage in thus attem^jting to 
 estahlish a parallelism between animal and vegetable processes ; rather would it 
 seem advantageous to keep prominently in view their contrasted, or at any rate 
 complementary characteristics, especially in the matter of the taking up of carhonic 
 acid and the giving up of oxygen on the one hand, and the taking in of oxygen 
 and the giving up of carbonic acid on the other. 
 
 But it is obvious that in latitudes where there is comparatively continuous 
 daylight during the periods of vegetation, the two actions — designated respectively 
 assimilation and growth — must go on much more simultaneously than where 
 there is a more marked alternation of daylight and darkness. In parts of Norway 
 and Sweden, for example, where, during the summer, there is almost continuous 
 daylight, crops of barley are grown with only from six to eight weeks inters'ening 
 from seed-time to harvest. A.nd Professor Schilbeler, of Ohi-istiania, after making 
 observations on the subject for nearly thirty years, has recently described the 
 characteristics of the vegetation developed under the influence of short summers 
 with almost continuous light. He states that, after acclimatisation, many gar- 
 den flowers increase in size and deptli of colour ; that there is a prevailing tinge 
 of red in the plants of the fjelds ; that the aroma of fruits is increased, and their 
 colour well developed, but that they are deficient in sweetness ; and that the deve- 
 lopment of essential oils in certain plants is greater than in the same plants grown 
 in other latitudes. Indeed, he considers it to be an established fact that light bears 
 the same relation to aroma as heat does to sweetness. 
 
 In connection with this question of the characters of growth under the influence 
 of continuous light, compared with those developed with alternate light and dark- 
 ness, the recent experiments of Dr. Siemens on the influence of electric light on 
 vegetation are of considerable interest. 
 
 In one series of experiments, he kept one set of plants entirely in the dark, a second 
 he exposed to electric light only, a third to daylight only, and a fourth to daylight, 
 and afterwards to electric light from 6 to 11 p.m. Those kept in the dark acquired 
 a pale yellow colour, and died ; those exposed to electric light only, maintained a 
 light green colour, and survived ; those exposed to daylight were of a darker green 
 colour, and were more vigorous ; and, lastly, those submitted to alternate daylight 
 and electric light, and but a few hours of darkness, showed decidedly greater 
 vigour, and, as he says, the green of the leaf was of a dark rich hue. He concluded 
 that daylight was t-sN-ice as effective as electric light ; but that, nevertheless, ' elec- 
 tric light was clearly sufiiciently powerful to form chlorophyll and its derivatives 
 in the plants.' 
 
 In a second series of experiments one group of plants was exposed to daylight 
 alone ; a second to electric light during eleven hours of the night, and was kept in 
 the dark during the day ; and a third to eleven hours day, and eleven hours electric 
 light. The plants in daylight showed the usual healthy appearance ; those in 
 alternate electric light and darkness were for the most part of a lighter colour ; 
 and those in alternate daylight and electric light far surpassed the others in dark- 
 ness of green and vigorous appearance generally. 
 
 I have carefully considered these general descriptions with a view to their 
 bearing on the question whether the characters developed under the influence of 
 electric light, and especially those under the influence of almost continuous light, 
 are more prominently those of assimilation or of growth ; but I have not been able 
 to come to a decisive opinion on the point. From some conversation I had with 
 Dr. Siemens on the subject, I gather that the characteristics were more those of 
 dark colour and vigour than of tendency to great extension in size. The dark green 
 colour we may suppose to indicate a liberal production of chlorophyll ; but if the 
 depth of colour was more than normal, it might be concluded that the chlorophyll 
 had not performed its due amount of assimilation work. In regard to this point, 
 attention may be called to the fact that Dr. Siemens refers to the abundance of the 
 blue or actinic rays in the electric arc, conditions which would not be supposed 
 
 c7 
 
14 
 
 specially to favour assimilation. On the other hand, the vigour, rather than charac-, 
 teristic extension in size, would seem to indicate a limitation of what is technically 
 called growth, under the influence of the almost continuous light. 
 
 Among the numerous field experiments made at Rothamsted, we have many 
 examples of great variation in depth of green colour of the vegetation growing on 
 plots side by side under known difierences as to manuring ; and we have abundant 
 evidence of difference of composition, and of rate of carbon-assimilation, coincidently 
 with these different shades of colour. One or two instances will strikingly illus- 
 trate the point under consideration. 
 
 There are two plots side by side in the series of experiments on permanent grass 
 laud, each of which received during six consecutive years precisely the same amount 
 of a mixed mineral manure, including potass, and the same amount of nitrogen in 
 the form of ammonia salts. After those six years, one of the two plots was still 
 manured in exactly the same way each year ; whilst the other was so, with one 
 exception — namely, the potass was now excluded from the manure. Calculation 
 shows that there was a great excess of potass applied during the first six years ; 
 and there was no marked diminution of produce during the five or six years suc- 
 ceeding the cessation of the application. But each year subsequently, up to the 
 present time, now a period of fourteen years, or of nineteen since the exclusion of the. 
 potass, the falling off in produce has beeil very great. ; 
 
 The point of special interest is, however, that all but identically the same 
 amount of nitrogen has been taken up by the herbage growing with the deficiency 
 of potass as by that with the continued supply of it. The colour of the vegetation 
 with the deficiency of potass has been very much darker green than that with the' 
 full supply of it. Nevertheless, taking the average of the eight years succeeding 
 the first six of the exclusion of the potass, there has been nearly 400 lbs. less carbon 
 assimilated per acre per annum ; and in some of the still later years the deficiency 
 has been very much greater than this. 
 
 We have here, then, the signiflcant fact that an equal amount of nitrogen was 
 taken up in both cases, that chlorophyll was abundantly produced, but that the fiill 
 amount of carbon was not assimilated. In other words, the nitrogen was there, the 
 chlorophyll was there, there was the same sun-light for both plots ; but the assimi- 
 lation-work was not done where there was not a due supply of potass. 
 
 Again, in the field in which barley has now been grown for twenty-nine years 
 in succession, there are two plots which have annually received the same amount of 
 nitrogen — the one in conjunction with salts of potass, soda, and magnesia ; and the 
 other with the same, and superphosphate of lime in addition. The plot without 
 the superphosphate of lime always maintains a darker green colour. At any given 
 period of growth the dry substance of the produce would undoubtedly contain a 
 higher percentage of nitrogen ; but there has been a deficient assimilation of carbon^ 
 amounting to more than 500 lbs. per acre per annum, over a period of twenty-eight 
 years. Here again, then, the nitrogen was there, the chlorophyll was there, the 
 sun-light was there, but the work was not done. 
 
 It may be stated generally that, in comparable cases, depth of green colour, if 
 not beyond a certain limit, maybe taken to mdicate corresponding activity of carbon 
 assimilation ; but the two instances cited are sufficient to show that we may, so far 
 as the nitrogen, the chlorophyll, and the light are concerned, have the necessary 
 conditions for full assimilation, but not corresponding actual assimilation. 
 
 It cannot, I think, fail to be recognised that in these considerations we have 
 opened up to view a very wide field of research, and some of the points involved 
 we may hope will receive elucidation from the further prosecution of Dr. Siemens's 
 experiments. He vnll himself, I am sure, be the first to admit that what he has 
 already accomplished has done more in raising than in settling important questions. 
 I understand that he proposes to submit plants to the action of the separated rays 
 of his artificial light, and the results obtained cannot fail to be of much interest. 
 But it is obvious that the investigation should now pass from its present initiative 
 character to that of a strictly quantitative enquiry. We ought to know not only 
 that, under ^ven conditions as to light, plants acquire a deeper green colour and 
 attain maturity much eariier than under others, but how much matter is assimi- 
 
15 
 
 lated in each case, and eometliing also of the comparatiTe chemical characters of 
 the products. As between the action of one description of light and another, and 
 as between the greater or less continuity of exposure, we ought to be able to form a 
 judgment whether the proper balance between assimilation on the one hand, and 
 growth and proper maturation on the other, has been attained ; whether the 
 plants have taken up nitrogen and mineral matter, and produced chlorophyll, in a 
 greater degree than the quantity and the quality of the light have been able to 
 turn to account ; or whether the conditions as to light have been such that the 
 processes of transfonnation and growth from the reserve material provided by 
 assimilation have not been normal, or have not kept pace v?ith the production of 
 that material. 
 
 But one word more in reference to Dr. Siemens's results and proposed extension 
 of his enquiries. Even supposing that by submitting grovraig crops to continuous 
 light by the aid of the electric light during the night, they could be brought to 
 maturity within a period shorter than at present approximately in proportion to 
 the increased number of hours of exposure, the estimates of the cost of illuminating 
 tbe vegetation of an acre of land certainly do not seem to hold out any hope that 
 agriculture is likely to derive benefit from such an application of science to its 
 needs. If, however, the characters of growth and of maturation should prove to 
 be suitable for the requirements of horticultural products of luxury and high value, 
 it may possibly be otherwise vvith such productions. 
 
 The above considerations obviously suggest the question : What is the oifice of 
 chlorophyll in the processes of vegetation ? Is it, as has generally been assumed, 
 confined to eflfecting, in some way not yet clearly understood, carbon assimilation, 
 and, this done, its function ended ? Or is it, as Pringsheim has recently suggested, 
 chiefly of avail in protecting the subjacent cells and their contents from those rays 
 of light which would be adverse to the secondary processes which have been dis- 
 tinguished as growth ? 
 
 Appropriate as it would seem that I should attempt to lay before you a risumi 
 of results bearing upon the points herein involved, so numerous and so varied have 
 been the investigations which have been undertaken on the several branches of the 
 question in recent years, that adequately to discuss them would occupy the whole 
 time and space at my disposal. I must therefore be content thus to direct atten- 
 tion to the subject and pass on to other points. 
 
 It has been shown that the plant may receive abundance of nitrogen, may pro- 
 duce abundance of chlorophyll, and may be subject to the influence of sufficient 
 light, and yet not assimilate a due amount of carbon. On the other hand, it has 
 been seen that the mineral constituents may be liberally provided, and yet, in the 
 absence of a sufticient supply of nitrogen in an available condition, the deficiency in 
 the assimilation of carbon wiU be still greater. In fact, assuming all the other 
 necessary conditions to be provided, it was seen that the amount of carbon assimi- 
 lated depended on the available supply of nitrogen. 
 
 In a certain general sense it may be said that the success of the cultivator may 
 be measured by the amount of carbon he succeeds in accumulating in his crops. 
 And as, other conditions being provided, the amount of carbon assimilated depends 
 on the supply of nitrogen in an available form within the reach of the plants, it is 
 obvious that the question of the sources of the nitrogen of vegetation is one of first 
 importance. Are they the same for all descriptions of plants P Are they to be 
 sought entirely in the soil, or entirely in the atmosphere, or partly in the one 
 and partly in the other ? „, ,. , ,. 
 
 These are questions which Mr. Lawes and myselt have discussed so frequently 
 that it might seem some apology was due for recurring to the_ subject here, espe- 
 cially as I referred to it iu some of its aspects before this Section at the Sheffield 
 Meeting last year. But the subject still remains one of first importance to agri- 
 culture, and it could not be omitted from consideration in such a review as I have 
 undertaken to give. Moreover, there are some points connected with it stUl un- 
 settled, and some still disputed. ^t. ^ , ^ j-j . 
 
 It will be remembered that Pe Saussure's conclusion was that plants did not 
 assimilate the free or uncombined nitrogen of the atmosphere, and that they 
 
16 
 
 derived their nitrogen from the compounds of it existing in the atmosphere, and 
 especially in the soil. Liehig, too, concluded that plants do not assimilate nitrogen 
 from the store of it existing in the free or uncombined state, but that ammonia 
 was their main source, and he assumed the amount of it annually coming down in 
 rain to be much more than we now know to be the case. 
 
 Referring to our previous papers for full details respecting most of the points 
 in question, I will state, as briefly as I can, the main facts known — first in regard 
 to the amount of the measurable, or as yet measured, annual deposition of combined 
 nitrogen from the atmosphere ; and secondly as to the amount of nitrogen annually 
 assimilated over a given area by different crops — so that some judgment may^ 
 be formed as to whether the measured atmospheric sources are suiRcient for the 
 requirements of agricultural production, or whether, or where, we must look for 
 other supplies ? 
 
 First, as to the amount of combined nitrogen coming down as ammonia and 
 nitric acid in the measured aqueous deposits from the atmosphere. 
 
 Judging from the results of determinations made many years ago, partly by 
 Mr. Way, and partly by ourselves, in the rain, &c., collected at Rothamsted ; from 
 the results of numerous determinations made much more recently by Professor 
 Frankland in the deposits collected at Rothamsted, and also in rain collected 
 elsewhere ; from the results obtained by Boussingault in Alsace ; from those of 
 Mari6-Davy at the Meteorological Observatory at Montsouris, Paris ; and from 
 those of many others made in France and Germany — we concluded, some years 
 ago, that the amount of combined nitrogen annually so coming down from the 
 atmosphere would not exceed 8 or 10 lbs. per acre per annum in the open country 
 in Western Europe. Subsequent records would lead to the conclusion that this 
 estimate is more probably too high than too low. And here it may be mentioned 
 in passing, that numerous determinations of the nitric acid in the drainage water 
 collected from land at Rothamsted, which had been many years Tinmanured, indicate 
 that there may be a considerable annual loss by the soil in that way ; indeed, pro- 
 bably sometimes much more than the amount estimated to be aimually available 
 from the measured aqueous deposits from the atmosphere. 
 
 It should be observed, however, that the amount of combined nitrogen, especially 
 of ammonia, is very much greater in a given volume of the minor aqueous deposits 
 than it is in rain ; and there can be no doubt that there would be more deposited 
 within the pores of a given area of soil than on an equal area of the non-porous 
 even surface of a rain-gauge. How much, however, might thus be available beyond 
 that determined in the collected and measured aqueous deposits, the existing 
 evidence does not afford the means of estimating with any certainty. 
 
 The next point to consider is — What is the amoimt of nitrogen annually 
 obtained over a given area, in different crops, when they are grown without any 
 supply of it in manure ? The field experiments at Rothamsted supply important 
 data relating to this subject. 
 
 Thus, over a period of 32 years (up to 1876 inclusive), wheat yielded an average 
 of 20-7 lbs. of nitrogen per acre per annum, without any manure ; but the annual 
 yield has declined from an average of more than 25 lbs. over the first 8, to less than 
 16 lbs. over the last 12, of those 32 years ; and the yield (it is true with several 
 bad seasons), has been still less since. 
 
 Over a period of 24 years, barley yielded 18'3 lbs. of nitrogen per acre per 
 annum, without any manure ; with a decline from 22 lbs. over the first 12, to only 
 14'6 lbs. over the next 12 years. 
 
 With neither wheat nor barley did a complex mineral manure at all materially 
 increase the yield of nitrogen in the crops. 
 
 A succession of so-called ' root crops ' — common turnips, Swedish turnips, and 
 sugar beet (with 3 years of barley intervening after the first 8 years) — 
 yielded, with a complex mineral manure, an average of 26'8 lbs. of nitrogen per 
 acre per annum over a period of 31 years. The yield declined from an average of 
 42 lbs. over the first 8 years, to only 13'1 .lbs. (in sugar beet) over the last 6 of 
 the 31 years ; but it has risen somewhat during the subsequent 4 years, with a 
 change of crop to mangolds. 
 
17 
 
 'With the leguminous crop, beans, there was obtained, over a period of 24 years, 
 SI '3 lbs. of nitrogen per acre per annum without any manure, and 45-5 lbs. with a 
 complex mineral manure, including potass (but without nitrogen). Without 
 manure the yield declined from 48-1 lbs. over the first 12 years to only 14'6 lbs. 
 over the last 12 ; and with the complex mineral manure it declined from 61'5 lbs. 
 over the first 12, to 29-5 lbs. over the last 12, years of the 24. 
 
 Again, an ordinary rotation of crops — of turnips, barley, clover or beans, and 
 wheat — gave over a period of 28 years an average of 86-8 lbs. of nitrogen per acre 
 per annum without any manure, and of 45'2 lbs. with superphosphate of lime alone, 
 applied once every four years, tha,t is for the root crop. Both without manure, and 
 with superphosphate of lime alone, there was a considerable decline in the later 
 courses. 
 
 A very remarkable instance of nitrogen yield is the following — in which the 
 results obtained when barley succeeds barley, that is when one gramineous crop 
 succeeds another, are contrasted with those when a leguminous crop, clover, inter- 
 venes between the two cereal crops. Thus, after the growth of six grain crops in 
 succession by artificial manures alone, the field so treated was divided, and, in 1873, 
 on one haK barley, and on the other half clover, was grown. The barley yielded 
 37 '3 lbs. of nitrogen per acre, but the three cuttings of clover yielded 151 '3 lbs. 
 In the next year, 1874, barley succeeded on both the barley and the clover portions 
 of the field. Where barley bad previously been grown, and had yielded 37'3 lbs. 
 of nitrogen per acre, it now yielded 39'1 lbs. ; but where the clover had previously 
 been grown, and had yielded 161'3 lbs. of nitrogen, the barley succeeding it gave 
 69'4 lbs., or 80'3 lbs. more after the removal of 161'3 lbs. in clover, than after the 
 removal of only 37'3 lbs. in barley. 
 
 Nor was this curious result in any way accidental. It is quite consistent with 
 agricultural experience that the growth and removal of a highly nitrogenous 
 leguminous crop should leave the land in high condition for the growth of a grami- 
 neous corn crop, which characteristically requires nitrogenous manuring ; and the 
 determinations of nitrogen in numerous samples of the soil taken from the two 
 separate portions of the field, after the removal of the barley, and the clover, respec- 
 tively, concurred in showing considerably more nitrogen, especially in the first 
 9 inches of depth, in the samples from the portion where the clover had been 
 grown, than in those from the portion whence the barley had been taken. Here, 
 then, the surface soil at any rate, had been considerably enriched in nitrogen by the 
 growth and removal of a very highly nitrogenous crop. 
 
 Lastly, clover has now been grown for twenty-seven years in succession, on a 
 small plot of garden ground vrhich had been under ordinary garden.cultivation for 
 probably two or three centuries. In the fourth year after the commencement of the 
 experiment, the soil was found to contain, in its upper layers, about four times as 
 much nitrogen as the farm-arable-land surrounding it ; and it would doubtless be 
 correspondingly rich in other constituents. It is estimated that an amount of nitro- 
 gen has been removed in the clover crops grown, corresponding to an average of not 
 far short of two hundred pounds per acre per annum ; or about ten times as much as 
 in the cereal crops, and several times as much as in any of the other crops, growing 
 on ordinary arable land ; and, although the yield continues to be very large, there 
 has been a marked decline over the second half of the period compared with the 
 first. Of course, calculations of the produce of a few square yards into quantities 
 per acre can only be approximately correct. But there can at any rate be no doubt 
 whatever, that the amount of nitrogen annually removed has been very great ; and 
 very far beyond what it would be possible to attain on ordinary arable land ; where, 
 indeed, we have not succeeded in getting even a moderate growth of clover for more 
 than a very few years in succession. 
 
 One other illustration should be given of the amounts of nitrogen removed from 
 a given area of land by different descriptions of crop, namely, of the results obtained 
 when plants of the gramineous, the leguminous, and other families, are growing 
 together, as in the mixed herbage of grass-land. 
 
 It is necessary here to remind you that gramineous crops gi-own separately on 
 arable land, such as wheat, barley, or oats, contain a comparatively small percentage 
 
18 
 
 of nitrogen, and assimilate a comparatively small amount of it over a given area. 
 Yet, nitrogenous manui'es have generally a very striking effect in increasing the 
 growth of such crops. The highly nitrogenous leguminous crops (such as heans and 
 clover), on the other hand, yield, as has heen seen, very much more nitrogen over a 
 given area, and yet they are by no means characteristically benefited by direct 
 nitrogenous manuring; whilst, as has been shovsna, their growth is considerably 
 increased, and they yield considerably more nitrogen over a jriven area, under the 
 influence of purely mineral manures, and especially of potass manures. Bearing 
 these facts in mind, the following results, obtained on the mixed herbage of grass 
 land, will be seen to be quite consistent. 
 
 A plot of such mixed herbage, left entirely unmanured, gave over twenty years', 
 an average of 3-3 pounds of nitrogen per acre per annum. Over the same period 
 another plot, which received annually a complex mineral manure, including potass, 
 dm'ing the first six years, but excluding it during the last fourteen years, yielded 
 46'3 lbs of nitrogen ; whilst another, which received the mixed mineral manure, 
 including potass, every year of the twenty, yielded 55-6 lbs. of nitrogen per acre 
 per annum. "Without manure, there was some decline of yield in the later years ; 
 with the partial mineral manuring there was a greater decline ; but with the com-' 
 plete noineral manuring throughout the whole period, there was even some increase 
 in the yield of nitrogen in the later years. 
 
 Now, the herbage growing without manure comprised about fifty species, repre- 
 senting about twenty natural families ; that growing with the limited supply of 
 potass comprised fewer species, but a larger amount of the produce, especially in 
 the earlier years, consisted of leguminous species, and the yield of nitrogen was 
 greater. Lastly, the plot receiving potass every- year yielded still more leguminous 
 herbage, and, accordingly, still more nitrogen. 
 
 The most striking points brought out by the foregoing illustrations are the 
 following : — ■ 
 
 First. Without nitrogenous manure, the gramineous crops annually yielded, for 
 many years in succession, much more nitrogen over a given area than is accounted 
 for by the amount of combined nitrogen annually coming down in the measured 
 aqueous deposits from the atmosphere. 
 
 Second. The root crops yielded more nitrogen than the cereal crops, and the 
 leguminous crops very much more still. 
 
 Third. In all cases — whether of cereal crops, root crops, leguminous crops, or a 
 rotation of crops — the decline in the annual yield of nitrogen, when none was supplied, 
 was very yreat. 
 
 How are these results to be explained ? Whence comes the nitrogen ? and 
 especially whence comes the much larger amount taken up by plants of the 
 leguminous and some other families, than by the graminese ? And, lastly, what is 
 the significance of the great decline in the yield of nitrogen in all the crops when 
 none is supplied in the manure ? 
 
 Many explanations have been offered. It has been assimied that the combined 
 nitrogen annually coming down from the atmosphere is veiy much larger than we 
 have estimated it, and that it is sufficient for all the requirements of annual growth. 
 It has been supposed that ' broad-leaved plants ' have the power of taking up nitro- 
 gen in some form from the atmosphere, in a degree, or in a manner, not possessed by 
 the narrow-leaved graminese. It has been argued that, in the last stages of the 
 decomposition of organic matter in the soU, hydrogen is evolved, and that this 
 nascent hydrogen combines with the free nitrogen of the atmosphere, and so forms 
 ammonia. It has been suggested that ozone may be evolved in the oxidation of 
 organic matter in the soil, and that, uniting with free nitrogen, nitric acid would be 
 produced. Lastly, it has by some been concluded that plants assimilate the free 
 nitrogen of the atmosphere, and that some descriptions are able to do this in a 
 greater degree than othei'S. 
 
 We have discussed thege various points on more than one occasion ; and we have 
 given our reasons for concluding that none of the explanations enumerated can be 
 taken as accounting for the facts of growth. 
 
 Confining attention here, to the question of the assimilation of free nitrogen by 
 
19 
 
 plants, it is obvious that, if this were established, most of our difficulties would 
 vanish. This question has been the subject of a great deal of experimental enquiry, 
 from the time that Boussingault entered upon it, about the year 1837, nearly up to the 
 present time. About twenty years ago it was elaborately investigated at Botham- 
 sted. In publishing the results of that enquiry, those of others relating to it were 
 fully discussed ; and although the recorded evidence is admittedly very conflicting, 
 we then came to the conclusion, and still adhere to it, that the balance of the direct 
 experimental evidence on the point is decidedly against the supposition of the assi- 
 milation of free nitrogen by plants. Indeed, the strongest argument we know of in 
 its favour, is, that some such explanation is wanted. 
 
 Not only is the balance of direct experimental evidence against the assumption 
 that plants assimilate free or uncombined nitrogen, but it seems to us that the 
 balance of existing indirect evidence is also in favour of another explanation of our 
 difficulties. 
 
 I have asked what is the significance of the gradual decline of produce of all 
 the different crops when continuously grown without nitrogenous manure? It 
 cannot be that, in growing the same crop year after year on the same land, there ia 
 any residue left in the soil that is injtirious to the subsequent growth of the same 
 description of crop ; for (excepting the beans) more of each description of crop has 
 been grown year after year on the same land than the average yield of the country 
 at large under ordinary rotation, and ordinary treatment— provided only, that suit- 
 able soil-conditions were supplied. Nor can the diminishing produce, and the 
 diminishing yield of nitrogen, be accounted for on the supposition that there was a 
 deficient supply of available mineral constituents in the soU. For, it has been shown 
 that the cereals yielded little more, and declined nearly as much as without 
 manure, when a complex mineral manure was used, such as was proved to be ade- 
 quate when available nitrogen was also supplied. So far as 'the root crops are con- 
 cerned, the yield of nitrogen, though it declined very much, was greater at first, and 
 on the average, than in the case of the cereals. As to the leguminosse, which re- 
 quire so much nitrogen from somewhere, it is to be observed that on ordinary arable 
 land the yield has not been maintained under any conditions of manuring; and the 
 decline was nearly as marked with mineral manures as without any manure. Com- 
 pared with the growth of the leguminosae on arable land, the remarkable result with 
 the garden clover woiild seem clearly to indicate that the question was one of soil, 
 and not of atmospheric supply. And the fact that all the other crops will yield 
 full agricultural results even on ordinary arable land, when proper manures are 
 applied, is surely very strong evidence that it is with them, too, a question of soil, 
 and not of atmospheric supply. 
 
 But we have other evidence leading to the same conclusion. Unfortunately 
 we have not reliable samples of the soil of the different experimental fields taken at 
 the commencement of each series of experiments, and subsequently at stated inter- 
 vals. We have, nevertheless, in some cases, evidence sufficient to show whether or 
 not the nitrogen of the soil has suffered diminution by the continuous growth of the 
 crop without nitrogenous manure. 
 
 Thus, we have determined the nitrogen in the soil of the eoBtinuously unma- 
 nured wheat plot at several successive periods, and the results prove that a gradual 
 reduction in the nitrogen of the soil is going on ; and, so far as we are able to form a 
 judgment on the point, the diminution is approximately equal to the nitrogen taken 
 out in crops; and the amount estimated to he received in the annual rain-fall is approxi- 
 mately balanced by the amount lost by the land as nitrates in the drainage water. 
 
 In the case of the continuous root-crop soil, on which the decline in the yield of 
 nitrogen in the crop was so marked, the percentage of nitrogen, after the experiment 
 had been continued for twenty-seve"n years, was found to be lower where no nitrogen 
 had been applied than in any other arable land on the farm which has been 
 examined. 
 
 In the case of the experiments on the mixed herbage of grass land, the soil of the 
 plot which, under the influence of a mixed mineral manure, including potass, had 
 yielded such a large amount of leguminous herbage and such a large amount of 
 nitrogen, showed, after twenty years, a considerably lower percentage of nitrogen 
 than that of any other plot in the series. 
 
20 
 
 Lastly, determinations of nitrogen in the garden soil which has yielded so much' 
 nitrogen in clover, made in samples collected in the fourth and the twenty-sixth 
 years of the twenty-seven of the experiments, show a very large diminution in the 
 percentage of nitrogen. The diminution, to the depth of 9 inches only, represents 
 approximately three-fourths as much as the amount estimated to he taken out in 
 the- clover during the intervening period ; and the indication is, that there has been 
 a considerable reduction in the lower depths also. It is to be supposed, however, 
 that there would be loss in other ways than by the crop alone. 
 
 I would ask, Have we not in these facts — that full amounts of the different crops 
 can be grown, provided proper soil-conditions are supplied ; that without nitrogenous 
 manure the yield of nitrogen in the crop rapidly declines ; and that, coincidently 
 with this, there is a decline in the percentage of nitrogen in the soil — have we not 
 in these facts cumulative evidence pointing to the soil, rather than to the atmosphere, 
 as the source of the nitrogen of our crops ? 
 
 In reference to this point, I may mention that the ordinary arable soil at.Rotham- 
 sted may be estimated to contain about 3,000 lbs. of nitrogen per acre in the first 
 9 inches of depth, about 1,700 lbs. in the second 9 inches, and about 1,600 lbs. in 
 the third 9 inches — or a total of about 6,200 lbs. per acre to the depth of 27 
 inches. 
 
 In this connection, it is of interest to state that a sample of Oxford clay, obtained 
 in the sub-Wealden exploration boring, at a depth of between 500 and 600 feet 
 (and which was kindly given to me by the President of the Association, Professor 
 Ramsay, some years ago), showed, on analysis at Rothamsted, approximately the 
 same percentage of nitrogen as the subsoil at Rothamsted taken to the depth of 
 about 4 feet only. 
 
 Lastly, in a letter received from Boussingault some years ago; referring to the 
 sources whence the nitrogen of vegetation is derived, he says : — 
 
 ' From the atmosphere, because it furnishes ammonia in the form of carbonate, 
 nitrates, or nitrites, and various kinds of dust. Theodore de Saussure was the first 
 to demonstrate the presence of amjnonia in the air, and consequently in meteoric 
 waters. Liebig exaggerated the influence of this ammonia on vegetation, since he 
 went so far as to deny the utility of the nitrogen which forms a part of farm-yard 
 manure. This influence is nevertheless real, and comprised within limits which 
 have quite recently been indicated in the remarkable investigations of M. Schlbsing. 
 
 ' From the soil, which, besides furnishing the crops with mineral alkaline sub- 
 stances, provides them with nitrogen, by ammonia, and by nitrates, which are 
 formed in the soil at the expense of the nitrogenous matters contained in diluvium, 
 which is the basis of vegetable earth ; compounds in which nitrogen exists in stable 
 combination, only becoming fertilising by the effect of time. If we take into 
 account their immensity, the deposits of the last geological periods must be con- 
 sidered as .an inexhaxistible reserve of fertilising agents. Forests, prairies, and 
 some vineyards have really no other manures than what are furnished bv the 
 atmosphere and by the soU. Since the basis of all cultivated land contains 
 materials capable of giving rise to nitrogenous combinations, and to mineral sub- 
 stances, assimilable by plants, it is not necessary to suppose that in a system of 
 cultivation the excess of nitrogen found in the crops is derived from the free nitro- 
 gen of the atmosphere. As for the absorption of the gaseous nitrogen of the air by 
 vegetable earth, I am not acquainted with a single irreproachable observation that 
 establishes it ; not only does the earth not absorb gaseous nitrogen, but it gives it 
 off, as you have observed in conjunction with Hr. Lawes, as Reiset has shown in 
 the case of dung, as M. Schlosing and I have proved in our researches on nitri- 
 fication. 
 
 ' If there is one feet perfectly demonstrated in physiology, it is this of the non- 
 assimilation of free nitrogen by plants ; and I may add by plants of an inferior 
 order, such as mycoderms and mushrooms (Translation).' 
 
 If, then, our soils are subject to a continual loss of nitrogen by drainage pro- 
 hably in many cases more than they receive of combined nitrogen from the atmo- 
 sphere — if the nitrogen of our crops is derived mainly from the soil, and not from 
 the atmosphere — and if, when due return is not made from without, we are draw- 
 
21 
 
 ing upon -what may be tenned the store of nitrogen of the soil itself — is there 
 not, in the case of many soik at any rate, as much danger of the exhaustion of 
 their available nitrogen as there has been supposed to be of the exhaustion of their 
 available mineral constituents P 
 
 I had hoped to say something more about soils, to advance our knovrledge re- 
 specting -which an immense amount of investigation has been devoted of late years, 
 but in regard to vrhich we have yet very much more to learn. I must, however, 
 now turn to other matters. 
 
 I have thus far directed attention to some points of importance in connection 
 with the sources of the constituents of our crops, and I must now brieily refer to 
 some in connection with the composition, and to some relating to the uses, of the 
 crops themselves. 
 
 As to composition, I must confine myself to indicating something of what is 
 known of the condition of the nitrogen in our various crops ; though I had intended 
 to say something respecting the carbo-hydrates, and especially respecting the 
 various members of the cellulose group. 
 
 As to the nitrogen — in our first experiments onthefeedingof animals, made in 1847, 
 1848, and 1849, the results of which were published in the last-mentioned year — 
 we found that, in the case of succulent roots used as food, not only were they not 
 of value as food in proportion to their richness in nitrogen, but when the percentage 
 of it was higher than a certain normal amount, indicating relative succulence and 
 immaturity, they were positively injurious to the animals. So marked was the 
 variation of result according to the condition of maturity or otherwise of the 
 foods employed, that, when reviewing the results of the experiments which had up 
 to that time been conducted, in a paper read before this Section of the British 
 Association at the Belfast Meeting in 1852 (and which was published in fiill in the 
 annual volume '), we stated that the mode of estimating the amount of proteine 
 compounds by multiplying the percentage of nitrogen by 6'3 was far from accurate, 
 especially when applied to succulent vegetable foods, and that the individual com- 
 pounds ought to be determined. The Rothamsted Laboratory stafi^ was, however, 
 much smaller then than it is now, and with the pressure of many other subjects upon 
 us, it was at that time quite impossible to follow up the enquiry in that direction. 
 
 It is, indeed, only within the last ten years or so, that the question has been 
 taken up at aU systematically ; but we are already indebted to E. Schulze, A. 
 Urick, Church, Sachsse, Maercker, Kellner, Vines, Emmerling, and others, for 
 important results relating to it. _ 
 
 Our knowledge in regard to the subject is, however, still very imperfect. But 
 it is in progress of investigation from two distinctly difierent points of view — from 
 that of the vegetable physiologist, and that of the agricultural chemist. The 
 veo-etable physiologist seeks to trace the changes that occur in the germination of 
 the seed, and during the subsequent life-history of the plant, to the production of 
 seed again. The agricultural chemist takes the various vegetable products in the 
 condition in which they are used on the farm, or sold from it. And as a very large 
 proportion of what is grown, such as grass, hay, roots, tubers, and various green 
 crops, are not matured productions, it comes to be a matter of great importance to 
 consider whether or not any large proportion of the nitrogenous contents of such 
 products is in such condition as not to be of avail to the animals which consume 
 them in their food ? . .,,.,,.,, 
 
 We cannot say that the whole of the nitrogen m the seeds with which we have 
 to deal exists as albuminoids. But we may safely assume that the nearer they 
 approach to perfect ripeness, the less of non-albuminoid nitrogenous matters will 
 they contain ; and, in the case of the cereal grains at any rate, it is probable that if 
 really perfectly ripe they will contain very nearly the whole of their nitrogen as 
 albuminoids. With regard to some leguminous and other seeds, which contain 
 peculiar nitrogenous bodies, the range may, however, be wider. 
 
 1 ' On the Composition of Foods in relation to Kespiration and the Feeding of 
 Animals.' 
 
22 
 
 But ■whatever the condition of the nitrogenous bodies in the seeds we grow or 
 sow, with germination begins a material change. Albuminoids are transformed 
 into peptones, or peptone-like bodies, or degraded into various amido- or other com- 
 pounds. Such change into more soluble and more diffusible bodies is, it is to be 
 supposed, essential to their free migration, and to their subserviency to the purposes 
 of growth. In the case of the germination, especially of some leguminous seeds, 
 asparagiue has been found to be a very prominent product of such degradation of 
 the albuminoids ; but it would seem that this disappears as the green parts are 
 developed. But now the plant begins to receive sup)3lies of nitrogen from the 
 soil, as nitrates or ammonia, and it would seem that amides constitute a consider- 
 able proportion of the produced nitrogenous bodies, apparently as an intermediate 
 stage in the formation of albuminoids. At any rate, such bodies are found to exist 
 largely in the immature plant ; whilst the amount of them diminishes as the plant, 
 or its various parts, approach to maturity. 
 
 But not only have we thus, in unripened vegetable productions, a greater or 
 less, and sometimes a very large, proportion of the nitrogenous bodies formed within 
 the plant, existing as amido-compounds, but we may have a large amount existing 
 in the juices as nitric acid, and some as ammonia, &c. Thus, E. Sohulze determined 
 the nitric acid in various ' roots ; ' and he found that, in some mangels, more than 
 one-third of the total nitrogen existed in that form, and about one-tenth as much 
 as ammonia. In a considerable series at Rothamsted, we have found an extremely 
 variable proportion existing as nitric acid, according to the size, succulence, or 
 degree of maturity, of the roots ; the amount being, as a rule, the least with the 
 ripest and less highly nitrogenous roots, and the most with the most succulent, 
 unripe, and highly nitrogenous ones. In some cases it reached as much as from 
 20 to nearly 30 per cent, of the total nitrogen. In many other immature vegetable, 
 products nitric acid and ammonia have been found ; but, so far as 1 remember, in 
 none in anything like so large a proportion as in the so-called ' root-crops,' es- 
 pecially mangels. In many, however, the quantity appears to be immaterial ; and 
 it is remarkable that whilst there is so much in the ' roots,' little or none is found 
 in potatos. 
 
 No wonder that, in the experiments already referred to, we found the feeding 
 result to be the worse the more succulent and immature the roots, and the higher 
 their percentage of nitrogen, accordingly. 
 
 But it is to the difference in amount of the albuminoid bodies themselves, in 
 different descriptions of vegetable produce, that I wish specially to direct attention, 
 making, however, some reference to what is known of the proportion of the 
 nitrogen existing as amido-oompounds. 
 
 In some mangels E. Schulze found only from about 20 to 22 per cent, of their 
 total nitrogen to exist as insoluble and soluble albumin. But he found in one case 
 32'5, and in the other 40'8, per cent, of the total nitrogen as amides. In a large 
 series of determinations at Rothamsted, by Church's method, we found a variation 
 of from under 20 to over 40 per cent, of the total nitrogen of mangels to exist as 
 albuminoids ; or, in other words, from nearly 60 to over 80 per cent, of it in the 
 non-albuminoid condition. 
 
 In potatos Schulze found from under 50 to 65 per cent, of the total nitrogen 
 as soluble and insoluble albumin, and from 27'7 to 49'1 per cent, as neutral and 
 acid amides. In a series of potatos grown at Rothamsted, under very various 
 conditions as to manuring, and in two different seasons, we found the nitrogen as 
 albuminoids to range from little over 50 to more than 71 per cent, of the total 
 nitrogen ; leaving, of course, from less than SO to nearly 50 per cent, to be 
 accounted for in other ways. 
 
 Kellner determined the amount of nitrogen as albuminoids, and as amido-com- 
 pounds, in a considerable series of green foods, both leguminous and gramineous, cut 
 at different stages of their growth. The proportion of the total nitrogen not as 
 albuminoids was, upon the whole, greater in the leguminosse than in the graminese. 
 In both, however, the proportion as albuminoids increased as the plants approached 
 to maturity. The proportion as albuminoids was in all these products very much 
 larger than in roots, and generally larger than in potatos. In the case of first-crop 
 
23 
 
 meadow hay, we found in the separated gramineous herbage 76'4, in the leguminous 
 herbage 82, and in the misoellaueous herbage 80'3 per cent of the nitrogen as 
 albuminoids ; and in the second crop 86'2 per cent, in the gramineous, 88'3 per 
 cent, in the leguminous, and 88'1 per cent, in the miscellaneous herbage. How far 
 the higher proportion of the nitrogen as albuminoide in the second crops is to be 
 taken as any indication of the characteristics of the autumn growth, or how far it is 
 to be attributed to the accidental condition of the weather, may be a question. 
 
 These illvistrations are suificient to give some idea of the range and proportion 
 of the nitrogen in different feeding crops which does not exist as albuminoids ; and 
 they are sufficient to show that a very large proportion of the non-albuminoid 
 matter exists as various amido-compounds. The question arises, therefore, whether 
 these bodies contribute in any way to the nutrition of the animals which feed upon 
 them ? We have but little experimental evidence on this point. As green herbage 
 is the natural food of many descriptions of animal, we might suppose that characr 
 teristic constituents of it would not be without some value as food ; but the culti- 
 vated root crops are much more artificial productions, and it is in them that we 
 find such a very large proportion of non-albuminoid nitrogen. With respect to 
 some of the amido-compounds, at any rate, direct experiments seem to show that 
 they are digested in the animal body, and increase the elimination of urea. Weiske 
 and Schrodt found that rabbits receiving, as their only nitrogenous food, either 
 asparagine or gelatin, wasted and died ; but a rabbit receiving both asparagine and 
 gelatin increased in weight and survived to the end of the experiment, which 
 lasted seventy-two days. From the results of other experiments made with sheep, 
 they concluded that both asparagine and gelatin protect the albuminoids of the 
 body from oxidation. 
 
 These considerations lead me, in conclusion, to refer briefly, and I promise 
 it shall be as briefly as is consistent with clearness, to the two very much disputed 
 questions of the origin of muscular power, and the sources of the fat of the animal 
 body. These subjects Mr. Lawes and myself have frequently discussed elsewhere ; 
 but as the controversy has assumed a new phase quite recently, it seems desirable 
 and appropriate that I should recur to it on the present occasion. 
 
 With regard to the question of the sources in the food of the fat of the animal 
 body, Liebig originally maintained that although tat might be formed from the 
 nitregenous compounds vdthin the body, the main source of it in the herbivora 
 was the carbo-hydrates. In his later writings, he sharply criticised the ex- 
 periments and arguments of those who have maintained the formation of fat chiefly 
 from the proteine compounds; but he at the same time seems to attach more 
 importance to that source than he formerly did. He gives it as his opinion that 
 the question cannot be settled by experiments with herbivora. He adds that what 
 we know with certainty is that, with these animals, albuminates and carbo- 
 hydrates work together to produce fat ; but whether the non-nitrogenous product, 
 fat, has its origin in the albumin or in the carbo-hydrate, he considers it not easy 
 to determine. 
 
 At the time when we commenced our experiments on the feeding of animals in 
 1 847, the question whether the fat of the animals fed for human food was mainly 
 derived from albuminoids or from carbo-hydrates had been scarcely raised, or at 
 least it was not prominent. The question then was rather— whether the herbivora 
 received their fat ready formed in their food, or whether it was produced within 
 the body— the latter view bemg that which Liebig had so forcibly urged, at the 
 same time mamtaining that at any rate its chief source was the carbo-hydrates. 
 Accordingly, our experiments were not specially arranged to determine whether or 
 not the whole of the fat produced could or could not be derived from the albu- 
 
 For each description of animal, oxen, sheep, and pigs, such foods as had been 
 established bv common experience to be appropriate were selected. The general 
 plan of the experiments was — to give to one set a fixed amount of a recognised good 
 food containing known quantities of nitrogen, fatty matter, &c. ; to another set the 
 same' amount of another food, of different characters in these respects ; to other 
 sets also fixed amoimts of other foods in the same way ; and then there was given, 
 
24 
 
 to the whole series, the same complementary food ad libitum. Or, to one set was 
 supplied a uniform food rich in nitrogen, and to others uniform foods poorer in 
 nitrogen, and so on, in each case ad libitum. 
 
 It will be seen that, in this way, a great variety of dietaries was arranged ; and 
 it wiU be observed that in each case the animals themselves fixed their consumption, 
 according to the requirements of the system. 
 
 As already indicated, the individual nitrogenous and non-nitrogenous compounds 
 of the foods were not determined. As a rule, the constituents determined were 
 — the total dry matter, the ash, the fatty matter, and the nitrogen ; from which last 
 the amount of nitrogenous compounds it might represent was calculated by the 
 usual factor. But, as already intimated, the results so obtained were only used with 
 considerable reservation, especially in the case of all immature vegetable produce. 
 Nor was the crude fibre determined ; but, as in the case of the estimated nitro- 
 genous substance, when interpreting the results, it was always considered whether or 
 not the food contained much or little of probably indigestible woody matter. 
 
 The animals being periodically weighed, we we're thus able to calculate the 
 amounts of the so-estimated nitrogenous substance, and of the total non-nitrogenous 
 substance, including and excluding fat, consumed— /or a ffiven live-weight within a 
 given time, and to produce a given amoumt of ina'ease in live-weight. 
 
 Experiments were made with a large number of sheep, and a large number of 
 pigs. And, even without rriaHng allowance for the different condition of the nitro- 
 genous or of the non-nitrogenous constituents, in comparable foods, the results ob- 
 tained uniformly indicated that both the amount consumed by a given live-weight of 
 animal within a given time, and that required to produce a given amoimt of increase, 
 were determined much more by the amoimt of the non-nitrogenous than by that of 
 the nitrogenous constituents which the food supplied. And when allowance was 
 made for the different condition of the nitrogenous constituents, and for the greater 
 or less amount of the non-nitrogenous ones which would probably be indigestible 
 and effete, the indications were still more remarkable and conclusive. 
 
 In very many cases the animals were slaughtered, and carefully examined as to 
 whether the tendency of development had been more that of grovrth in frame and 
 flesh, or in fatness. Here, again, the evidence was clear — that the tendency to growth 
 in frame and flesh was favoured by a high proportion of nitrogen in the food, and 
 that to the production of fat by a high proportion of digestible non-nitrogenous 
 constituents. 
 
 In a few cases the actual amount of fat in the animals in the lean, and in the fat 
 condition, was determined ; and the results admitted of no doubt whatever that a 
 very large proportion of the stored-up fat could not have been derived from the 
 fatty matter of the food, and must have been produced within the body. 
 
 So decisive and consistent were the very numerous and very varied results in 
 regard to these points, that we had no hesitation in concluding — not only that much 
 of the fat stored up was produced within the body, but that the source of much, 
 at any rate, of the produced fat must have been the non-nitrogenous constituents of 
 the food — in other words, the carbo-hydrates. 
 
 As already stated, however, as the question whether the source of the produced 
 fat was the proteine compounds or the carbo-hydrates was not then prominent, we 
 had not so arrangted the experiments as to obtain the largest possible increase in fat 
 with the smallest possible supply of nitrogenous compounds in the food ; nor did we 
 then even calculate whether or not there was suificient nitrogenous matter consumed 
 to be the source of the whole of the fat produced. 
 
 This question, indeed, excited very little interest, until, at a meeting of the 
 Congress of Agricultural Chemists held at Mimich in 1865 (at which I happened 
 to be present). Professor Voit, from the results of experiments made in Pettenkofer's 
 respiration apparatus with dogs fed on flesh, announced his conclusion that fat 
 must have been produced from the nitrogenous substance, and that this was probably 
 the chief, if not the only, source of the fat, even of herhivora — an opinion which he 
 subsequently urged much more positively. 
 
 In the discussion which followed the reading of Professor Voit's paper, Baron 
 Liebig forcibly called in question his conclusions ; maintaining not only that it was 
 inadmissible to form conclusions on such a point in regard to herbivofa, from the 
 
25 
 
 results of experiments made with carnivora, but also tlat direct quantitative results 
 obtained witli herbivorous animals had afforded apparently conclusive evidence in 
 favour of the opposite view. 
 
 Voit's paper excited considerable controversy, in which Mr. Lawes and myself 
 joined. We maintained that experiments to determine such a question should be 
 made, not with carnivora or omnivora fed on iiesh, but with herbivora fed on their 
 appropriate fattening food, and on such herbivora as common experience showed 
 to be pre-eminently fat-producers. We pointed out ' that the pig comprised, for a 
 given live-weight, a comparatively small proportion of alimentary organs and con- 
 tents ; that, compared with that of the ruminants, his food was of a high character, 
 yielding, for a given weight of it, much more total increase, much more fat, and 
 much less necessarily effete matter ; that, in proportion to his weight, he consumes 
 a larger amount of food, and yields a larger amount, both of total increase and of 
 fat, within a given time ; and, lastly, that he contains a larger proportion of fat, 
 both in a given live weight and in his increase whilst fattening. 
 
 It is obvious that, vnth these characteristics, there is much less probable range 
 of error in calculating the amount and the composition of the increase in live-weight 
 in relation to the amount and composition of the food consumed, than in the case 
 of the ruminants; and that, therefore, the pig is very much more appropriate for 
 the purpose of experiments to determine the sources in its food of the fat it pro- 
 duces. 
 
 Accordingly, we calculated a number of our early experiments made with pigs, 
 to determine whether or not the nitrogenous substance they consumed was suffi- 
 cient for the formation of the fat they produced. For simplicity of illustration, and 
 to give every possible advantage to the view that nitrogenous substance might have 
 been the source of the produced fat, we assumed the whole of the crude fat of the 
 food to have been stored up in the animal — thus estimating a minimum amount to 
 be produced. Then, again, we supposed the whole of the nitrogenous substance of 
 the food to be perfectly digested, and to become available for the purposes of the 
 system. Lastly, after deducting the amount of nitrogenous substance estimated to 
 be stored up as such, the whole of the remainder was reckoned to be so broken up 
 that no other carbon-compounds than fat and urea would be produced. 
 
 The result was, that, even adopting these inadmissible assumptions, in all the 
 cases in which, according to common experience, the food was admittedly the most 
 appropriate for the fattening of the animal, the calculation showed that a large 
 amount of fat had been produced which could not have been derived from the 
 nitro°'enous substance of the food, and must therefore have had its source in the 
 carbo-hydrates. Such a result is, moreover, entirely accordant with experience in 
 practical feeding. 
 
 Eeviewing the whole subject in great detail in 1869, Professor Voit refers to 
 these results and calculations. He confesses that he has not been able to get a 
 general view of the experiments from the mass of figures recorded, and from his 
 comments he shows that he has on some points misunderstood them. He admits, 
 however, that, as the figures stand, it would appear that fat had, in some instances, 
 been derived from the carbo-hydrates. Still, he says, he cannot allow himseH to 
 consider that a transformation of carbo-hydrates into fat has thus been proved. 
 
 Professor EmU von Wolff, again, in his Lnndmrthschnftliche FutterungiileJire, 
 referring to the same experiments, admits that they are almost incomprehensible 
 unless we assume the direct concurrence of the carbo-hydrates in the formation of 
 fat. He nevertheless, seems to consider that evidence of the land in question is in- 
 conclusive ; and he suggests that experiments with pigs should be made in a respi- 
 ration apparatus to determine the point. 
 
 Mr. Lawes and myself entertained, however, the utmost confidence that the 
 question was of easy settlement without any such apparatus, provided only suit- 
 able animals and suitable foods were selected. I, accordingly, gave a paper on the 
 subieotin the Section fur Land^drthgchqft-und Agricultur-Chemie, at the Natur- 
 forscher Versammlung held at Hamburg in 1876.* The points which I partiou- 
 
 1 ' On the Sources of the Fat of the Animal Body,' Phil. Mag., December 1866. 
 
 2 The substance of" that communication is given in the Jownal of Anatomy and 
 FTiysMlogy, vol. xi. part iv. 
 
26 
 
 larly insisted upon were — ^that the pig should be the subject of experiment ; that he 
 should be allowed to take as much as he would eat of his most appropriate fattening 
 food, so that his increase, and the fat he produced, should bear as large a proportion 
 as possible to his weight, to the total food, and to the total nitrogenous substance 
 consumed. Finally, it was maintained that, if these conditions were observed, and 
 the constituents of the food determined, and those of the increase of the animal 
 estimated according to recognised methods, the results could not faU to be perfectly 
 conclusive, without the intervention, either of a respiration apparatus, or of the 
 analysis of the solid and liquid matters voided. 
 
 Bfisults so obtained were adduced in proof of the correctness of the conclusions 
 arrived at. We at the same time admitted that, although, for reasons indicated, 
 we had always assumed that fat was formed from the carbo-hydrates in the case of 
 ruminants as well as of pigs, yet, as in our experiments with those animals we had 
 supplied too large amounts of ready formed fat, or of nitrogenous matter, or of 
 both, it could not be shown so conclusively by the same mode of calculation in 
 their case as in that of pigs. 
 
 In the discussion which followed. Professor Henneberg agreed that it seemed 
 probable that fat could be formed from the carbo-hydrates in the case of pigs. In 
 the case of experiments with other animals, however, the amount of fat produced 
 was too nearly balanced by the amount of fat and albuminous matters available, to 
 afford conclusive evidence on the point. 
 
 Quite recently. Professor Emil von ^o\S{Landwirthschaftliche Jahrhiicher, Band 
 viii. 1879, Supplement) has applied the same mode of calculation to results obtained 
 by himself with pigs some years ago. He concluded that the whole of the body 
 fat could not have been formed without the direct co-operation of the carbo-hydrates 
 of the food. But what is of greater interest stUL is, that he also calculated, in the 
 same way, the results of some then quite recent experiments of Henneberg, Kern, 
 and Wattenberg, with sheep. He thus found that, even including the whole of the 
 estimated amides with the albumin, there must have been a considerable production 
 of fat from the car^o-hydrates ; and, excluding the amides, the amount reckoned to 
 be derived from the carbo-hydrates was of course much greater. 
 
 I will only add, on this point, that, on re-calculating some of our early results 
 with sheep, which did not afford sufficiently conclusive evidence when the whole of 
 the nitrogen of the food was reckoned as albumin, show a very considerable forma- 
 tion of fat from the carbo-hydrates, if deduction be made for the probable amoimt of 
 non-albuminoid nitrogenous matter of the food. 
 
 We have now, then, the two agricultural chemists of perhaps the highest 
 authority, both as experimenters and writers on this subject on the Continent, 
 giving in their adhesion to the view, that the fat of the herbivora, which we feed 
 for human food, may be, and probably is, largely produced from the carbo-hydrates. 
 I dare say, however, that some physiologists will not change their view until Voit 
 gives them sanction by changing his, which, so far as I know, he has not yet done. 
 The question which has been currently entitled that of ' The Origin of Muscvlnr 
 Power,' or ' The Sources of Muscular Potoer,' has also been the subject of much 
 investigation, and of much conflict of opinion, since the first publication of Liebigs 
 views respecting it in 1843. 
 
 As I have already pointed out, he then maintained that the amount of muscular 
 tissue transformed, the amount of nitrogenous substance oxidated, was the measure 
 of the force generated in the body. He accordingly concluded that the requirement 
 for the nitrogenous constituents of food would be increased in proportion to the in- 
 crease of the force expended. In his more recent writings on the subject, he freely 
 criticises those who take an opposite view. He nevertheless grants that the secretion 
 of urea is not a measure of the force exerted ; but, on the other hand, he does not 
 commit himself to the admission that the oxidation of the carbo-hydrates is a source 
 of muscular power. 
 
 The results of our own early and very numerous feeding experiments were as 
 has been said, extremely accordant in showing that, provided the nitrogenous con- 
 stituents in the food were not below a certain rather limited amount, it was the 
 quantity of the digestible and available non-nitrogenous constituents, and not that 
 
27 
 
 of the nitrogenous substance, that determined — both the amount consumed hy a given 
 live-weight within a given time, and the amount of increase in live-weight produced. 
 They also showed that one animal, or one set of animals, might consume two or 
 three times as much nitrogenous substance in proportion to a given live-weight 
 within a given time as others in precisely comparable conditions as to rest or exercise. 
 It was further proved that they did not store up nitrogenous subtanee at all ia 
 proportion to the greater or less amount of it supplied in the food, but that the 
 excess reappeared in the liquid and solid matters voided. 
 
 So striking were these results, that we were led to turn our attention to human 
 dietaries, and also to a consideration of the management of the animal body under- 
 going somewhat excessive labour, as, for instance, the hunter, the racer, the 
 cab-horse, and the foxhound, and also pugilists and runners. Stated in a very few 
 words, the conclusion at which we an-ived from these enquiries (which were sum- 
 marised in our paper given at Belfast in 1852) was— that, unless the system were 
 overtaxed, the demand induced by an increased exercise of force was more charac- 
 terised by an increased requirement for the more specially respiratory, than for the 
 nitrogenous, constituents of food. 
 
 Soon afterwards, in 1854, we found by direct experiments with two animals in 
 exactly equal conditions as to exercise, both being in fact at rest, that the amount 
 of urea passed by one feeding on highly nitrogenous food was more than twice as 
 great as that fed on a food comparatively poor in nitrogen. 
 
 It was clear, therefore, that the rule which had been laid down by Liebig, and 
 which has been assumed to be correct by so many -n-riters, even up to the present 
 time, did not hold good — namely, that ' The sum of the mechanical effects pro- 
 duced in two individuals, in the same temperature, is proportional to the amount of 
 nitrogen in their urine ; whether the mechanical force has been employed in volun- 
 tary or involuntary motions, whether it has been consumed by the limbs or by the 
 heart and other viscera ' — unless, indeed, as has been assumed by some experi- 
 menters, there is, with increased nitrogen in the food, an increased amount of 
 mechanical force employed in the ' involuntary motions ' sufficient to accoimt for 
 the increased amount of urea voided. 
 
 The question remained in this condition untU 1860, when BischofF and Voit 
 published the results of a long series of experiments made with a dog. They found 
 that, even when the animal was kept at rest, the amount of urea voided varied 
 closely in proportion to the variation in tlie amount of nitrogenous substance 
 given in the food — a fact which they explained on the assumption that there must 
 have been a corresponding increase in the force exercised in the conduct of the 
 actions proceeding within the body itself in connection with the disposal of the 
 increased amount of nitrogeneous substance consumed. Subsequently, however, 
 they found that the amount of urea passed by the animal was, with equal condi- 
 tions as to food, &c., no greater when he was subjected to labour than when at 
 rest • whilst, on the other hand, the carbonic acid evolved was much increased 
 by such exercise. They accordingly somewhat modified their views. 
 
 In 1866 appeared a paper by Professors Ficli and WisUcenus, giving the results 
 obtained in a mountain ascent. They found that practically the amount of urea 
 voided was scarcely increased by the labour thus undertaken. Professor Frankland 
 gave an account of these experiments in a lecture at the Royal Institution in the 
 same year ; and he subsequently followed up the subject by an investigation of the 
 heat developed in the combustion of various articles of food, applying the results in 
 illustration of the phenomena of the exercise of force. 
 
 Lastly, KeUner has made some very interesting experiments with a horse at 
 Hohenheim, the results of which were pubhshed last year. In one series, the ex- 
 periment was divided into five periods, the same food being given throughout ; but 
 the animal accomplished different distances, and drew different weights, the draught 
 being measured by a horse-dynamometer. The changes in live-weight, the amount 
 of water drunk, the temperature, the amount of matters voided, and their contents 
 in nitrogen, were also determined. 
 
 The result was, that with only moderate labour there was no marked increase 
 in the nitrogen eliminated in the urine, but that with excessive labour the animal 
 
28 
 
 lost weight and eliminated more nitrogen. Kellner concluded, accordingly, that,, 
 under certain circumstances, muscular action can increase the transformation of 
 albumin in the organism in a direct way ; but that, nevertheless, in the first line 
 is the oxidation of the non-nitrogenous matters — carbo-hydrates and fat, next comes 
 in requisition the circulation-albumin, and finally the organ-albumin is attacked. 
 
 In reference to these conclusions from the most recent experiments relating to 
 the subjeoty we may wind up this brief historical sketch of the changes of view 
 respectmg it, with the following quotation from our own paper published in 
 1866 : * — ' ... all the evidence at command tended to show that by an increased 
 exercise of muscular power there was, with increased requirement for respirable 
 material, probably no increased production and voidance of urea, unless, owing to 
 excess of nitrogenous matter in the food, or a deficiency of available non-nitrogenous 
 substance, or diseased action, the nitrogenous constituents of the fluids or solids of 
 the body were drawn upon in an abnormal degree for the supply of respirable 
 material.' 
 
 In conclusion, although I fully agree with Voit, Zuntz, "Wolfi^, and others, that 
 there still remains much for both Chemistry and Physiology to settle in connection 
 with these two questions of The Sources of the Fat of the Animal Body' and ' The 
 Origin of Museular Power,' yet I think we may congratulate ourselves on the re- 
 establishment of the true faith in regard to them, so far at least as the most im- 
 portant practical points are concerned. 
 
 ' ' Food in its relation to various exigencies of the Animal Body.' — Phil. Mag. 
 July 1866. 
 
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