9 ANIMAL CHEMISTRY LECTURE Y. 



\vbile there is a corresponding increase, not of course an equal 

 increase, in the volume of its carbonic acid ; that the irritability 

 of muscular fibre out of the body is arrested by its removal from 

 oxygen, and again manifested on its re-exposure thereto ; and 

 lastly, that other things being equal, the amount of urea excreted 

 by the kidneys, and of carbonic acid excreted by the lungs, is 

 proportionate to the muscular activity of the individual. Seeing, 

 then, that muscular exertion is really dependent upon muscular 

 oxidation, we have to consider what should be the products, and 

 what the value of this oxidation. 



(104.) Unfortunately, the precise molecular formula the ex- 

 act chemical constitution of muscle is at present unknown. 

 But in muscle, as in all the albuminoid class of bodies, we do 

 know the ratio in which the constituent carbon and nitrogen 

 stand to one another. Thus it is established beyond all question 

 that the ratio of the number of atoms of carbon to the number 

 of the atoms of nitrogen in muscle is as nearly as possible, if not 

 quite exactly, four to one. In the most minute fragment of 

 muscle, then, for every single atomic proportion of nitrogen there 

 are four atomic proportions of carbon, thus : 



4 CARBON to i NITROGEN. 



It will be more convenient, however, to express this ratio by the 

 doubles of the above numbers, so that, instead of four to one, we 

 will adopt eight to two, as our expression of the atomic ratio of 

 carbon to nitrogen in every particle of muscle : 



8 CARBON to 2, NITROGEN. 



Admitting, further, as a result of its ultimate metamorphosis, 

 that the whole of the nitrogen of muscle is converted into urea, let 

 us first consider what proportion of its carbon must be associated 

 with thisnitrogen to produce urea, and what proportion be thereby 

 left for excretion in the form of carbonic acid. Now, although the 

 molecular constitution of muscle is undetermined, that of urea is 



