RESULTS OF MUSCLE OXIDATION. 99 



perfectly definite.* As shown by its formula, CN 2 H 4 0, the mole- 

 cule of urea consists of one atom of carbon, two atoms of nitro- 

 gen, four atoms of hydrogen, and one atom of oxygen. In other 

 words, leaving out of consideration its hydrogen and oxygen, the 

 atomic ratio of nitrogen to carbon in urea is as two to one. 

 Accordingly, every two atoms of nitrogen in urea have one atom 

 of carbon associated with them ; so that if we take the two pro- 

 portions of nitrogen existing in muscle and add to them the one 

 proportion of carbon necessary to form urea, we shall have seven 

 proportions of carbon left for conversion into carbonic acid, 

 thus : 



a NITROGEN 



The theoretical result, then, of the complete oxidation of 

 muscle is the appearance of one-eighth of its carbon in the form 

 of urea, and of seven- eighths of its carbon in the form of carbonic 

 acid. 



(105.) Now, let us see what is the actual result. We have two 

 series of experiments made by Bischof and Voit, and Pettenkofer 

 and Voit respectively, in which lean dogs were fed exclusively 

 upon a moderate diet of flesh. In the first series of experiments 

 a small proportion of fat left in the flesh was duly allowed for ; 

 while in the second series the fat was entirely removed. The 

 general results of the two series of experiments are shown 

 below : 



C. of Garb, acid C. of Urea 



7*29 to I Bischof and Voit 

 6-85 to i Pettenkofer and Voit 

 7 '07 to i Mean 



Thus the ratio of carbon excreted in the form of carbonic acid 

 to carbon excreted in the form of urea was as 7-29 to i in the 



* This mode of viewing the relationship of muscle to urea and carbonic 

 acid was suggested by Dr. Lyon Play fair's essay ' On the Food of Man in 

 relation to his Useful Work,' to which I am otherwise much indebted in the 

 early part of this lecture. 



H2 



