relations to various exigencies of the Animal Body. 63 



" involuntary motions " sufficient to account for the increased 

 amount of urea voided. 



It was at any rate obvious that, if the amount of urea voided 

 by one animal at rest could be from two to three times as great 

 as that voided by a similar animal also at rest, and under other- 

 wise equal conditions, provided only that the food of the one 

 contained from two to three times as much nitrogen as that of 

 the other, the amount of urea passed could not be any measure 

 of the amount of muscular power exerted; and this evidence, 

 considered in connexion with that relating to the demands of the 

 system not only of the fattening animal but of the animal body 

 fed with a view to mechanical exertion, afforded further confir- 

 mation of the view we had already put forward as above quoted, 

 and also led to the extension and more definite expression of it. 



The results of Bischoff and Voit, conducted through a period 

 of many months, with a dog, either submitted to hunger or fed 

 from time to time on foods containing very different amounts of 

 nitrogenous substance, showed a very variable amount of urea 

 voided, although the animal were kept under equal conditions 

 as to exercise. Still, on the publication of those results in 1860, 

 the authors assumed that although there had been no greater 

 exercise of force manifested in the form of external work, yet 

 when the amount of nitrogenous substance in the food was 

 greater, and the amount of urea voided correspondingly greater, 

 there must have been a corresponding increase in the force ex- 

 ercised in the conduct of the actions proceeding within the body 

 itself in connexion with the disposition of the increased amount 

 of nitrogenous substance consumed. When, however, they 

 subsequently found that the amount of urea passed by the 

 animal when subjected to somewhat severe labour was, other 

 things being equal, no greater than when at rest, whilst the 

 carbonic acid evolved was much increased by such exercise, their 

 view was of necessity somewhat modified. 



Again, the results of Dr. Edward Smith, which showed great 

 variation in the amount of urea passed when there was concur- 

 rent variation in the amount of nitrogenous substance in the 

 food, and comparatively little variation in the amount of urea 

 voided with great variation in the amount of labour performed, 

 but, on the other hand, great increase in the carbonic acid 

 evolved with increased exercise of force, obviously still farther 

 pointed to the correctness of the view that with muscular ex- 

 ertion there was a more marked increased demand for the non- 

 nitrogenous than for the nitrogenous constituents of food. 



That this was the necessary conclusion from the results of 

 our own investigations, and also from those of the researches of 

 Bidder and Schmidt, Bischoff, Yoit, Pettenkofer, E. Smith, and 

 others, we have frequently maintained. Indeed the view urged 



