526 



NA TURE 



\_Scpi. 30, 1880 



ill 1S76.' The points which I particularly 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 appro- 

 priate fattening food, so that his increase, and the fat he 

 produced, should bear as large a proportion as pDSsible to his 

 weight, to the total food, and to the total nitrogenous substance 

 consumed. Finally, it was maintained that, if these conditions 

 were obicrved and the constituents ol the food determined, pnd 

 those of the increase of the animal estimated according to recog- 

 nised methods, the results could not fail to be ]3erfectly conclusive 

 without the intervention either of a respiration apparatus or of 

 the analysis of the solid and liquid matters voided. 



Results 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 ahvays assumed that 

 fat was formed from the carbohydrates in the case of ruminants 

 as well as of pigs, yet, as in our experiments with those animals 

 we had supplied too lar,'e amounts of ready-formed fat, or of 

 nitrogenous matter, or of both, it could not be shown so con- 

 clusively, by the same mode of calculation in their case as in that 

 of pigs. 



In the discussion which followed. Prof. Henneberg agreed 

 that it seemed probable that fat could be formed from the carbo- 

 hydrates in the case of pig-. In the case of experiments wiih 

 otlier 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 Prof. Emil von Wolff {LandwirthschaftUche 

 jfiihi-bikhcT, Band viii. 1879, Supplement) has applied the same 

 mode of calculation to results obtained by himself with pigs 

 some years ago. lie concluded that the whole of the body fat 

 could not have been firmed without the direct co-operation of 

 the carbohydrates of the food. But what is of greater interest 

 still is that he also calculated in the same way the results of some 

 then quite recent experiments of Henneberg, Kern, and Watten- 

 berg, 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 carbohydrates ; and, 

 excluding the amides, the amount reckoned to be derived from 

 the carbohydrates was of course much greater. 



1 will only add, on this point, that on recalculating 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 formation of 

 fat from the carbohydrates if deduction be made for the probable 

 amount 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 ])robably 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 Muscular Power," or "The tiources of Muscular 

 Foiver," has also been the subject of much investigation, and of 

 much conflict of opinion, since the first publication of Liebig's 

 views respecting it in 1S42. 



As I have already pointed out, he then maintained that the 

 amount of muscular tissue transformed, the amount of nitro- 

 genous substance oxidated, w as 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 pro- 

 portion to the increase 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 tlie 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 carbohydrates is a source of muscular power. 



The results of our own early and very numerous feeding expe- 

 riments were, as has been said, extremely accordant in showing 

 that, provided the nitrogenous constituents 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 of the nitrogenous substance, that determined — both the 

 amount consumed by a given live-weight within a given time, and 

 the amount of increase in live-weight produced. They also 



The subsi.ince of that communication is given in the Journat 0/ 

 Anatomy and I'hyudl,ij;y, vol. xi. part iv. 



showed that one animal, or one set of animals, might consume 

 t« o or three times as much nitrogenous substance in proportion 

 to a given live-weight within a given time as others in precisely 

 comjiarable conditions as to rest or exercise. It was further 

 proved that they did not store up nitrogenous substance at all in 

 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 ths 

 management of the animal body undergoing somewhat excessive 

 labour, as, for instance, the hunter, the racer, the cab-horse, and 

 the foxhound, and abo pugilists and runners. Stated in a very 

 few words, the conclusion at which we arrived from these in- 

 quiries (which were summarised in our paper given at Belfast in 

 1852) was, thit unless the sy tem 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 

 \\ Titers, evennp to the present time, did not hold good — namely, that 

 " The sum of the mechanical effects produced 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 voluntary or involuntary motions, whether it has been con- 

 sumed by the limbs or by the heart and other viscera" — unless, 

 indeed, as has been assumed by some experimenters, there is, 

 with increased nitrogen in the food, an increased amount of 

 mechanical force employed in the "involuntary motions" 

 sufficient to account for the increased amount of urea voided. 



The quetion remained in this condition until 1S60, when 

 Bischoff and Voit published the results of a long series of ex- 

 periments 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 the 'amount of nitroge- 

 nous 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 nitrogenous sub-tance consumed. 

 Subsequently, however, they found that the amount of urea 

 passed by the animal was, with equal conditions 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 Fick and Wislicenus, 

 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. Prof. 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, Kellner has made some veiy interesting experiments 

 with a horse at Ilohenheim, the results of which were published 

 last year. In one series the experiment 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-dynamouieicr. 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 ; bitt 

 that with excessive labour the animal lost weight and ehminated 

 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, neverthe- 

 less, in the first line is the oxidation of the non-nitrogenous matters 

 — carbohydrates and fat, next comes in requisiiionthe circulation- 

 albumin, and finally the organ-albumin is attacked. 



lu reference to these conclusions from the inost recent experi- 



