690 WHENCE THE TAT AND BONES OF ANIMALS. 



the food contains the lime, the magnesia, the potash, the soda, the sul- 

 phur, the phosphorus, and the iron, which exist in the inorganic parts of 

 the animal body — so that the (question seems already resolved. The 

 body obtains from the food all the elements of which it consists, and 

 if these be not present in the food, the body of the animal cannot be 

 properly built up and supported. 



But to the chemist and physiologist the more important part of the 

 question still remains. In what slate do these elements enter into the 

 body ? Are the substances of which the food consists decomposed after 

 they are taken into the stomach ? Are their parts first torn asunder, and 

 then re-united in a different way, so as to form the chemical compounds 

 of which the muscles, bones, and blood consist ? Are the vital powers 

 bound to labour, as it were, for the existence and support of the body ? 

 Do they compound or build up out of their ultimate elements the various 

 substances of which the body is composed — or do they obtain these sub- 

 stances ready prepared from the vegetable food on which animals, in 

 general, are fed ? The answer which recent chemical researches give to 

 this second question forms one of the most beautiful contributions which 

 have been made to animal physiology in our time. 



1°. We have seen that the flour of wheat and of our other cultivated 

 grains consists in part of gluten, of albumen, or of casein. These sub- 

 stances all contain nitrogen, and are identical in constitution with each 

 other, and with the fibrin of which the muscles of animals chiefly con- 

 sist.* The substance of the muscles exists ready formed, therefore, in the 

 food which the animal eats. The labour of the stomach is in conse- 

 quence restricted to that of merely selecting these substances from the 

 food and dispatching them to the several parts of the body, where they 

 are required. The plant compounds and prepares the materials of the 

 muscles — the stomach only picks out the bricks, as it were, from the other 

 building materials, and sends them forward to be placed where they 

 happen to be wanted. 



2°. Again, we have seen that in all our crops, so far as they have 

 been examined, there exists a sensible proportion of fatty or oily maru'r 

 more or less analogous to the several kinds of fat which exist in the holies 

 of animals. In regard to this portion, therefore, of the body, the vege- 

 table performs also the larger part of the labour. It builds up fatty sub- 

 stances out of their elements — carbon, hydrogen, and nitrogen. These 

 substances the stomach extracts from the food, and the body appropriates 

 them, after they have been more or less slightly changed, in order to 

 adapt them to their several purposes. There may possibly be othi^r 

 sources of fat, as we shall hereafter see, but the simplest, the most na- 

 tural — and probably, where a sufficient supply exists, the only one had 

 recourse to by the healthy animal — is the fat which is found, re idy 

 formed, in the vegetable food it eats. 



3°. Further, the bones, the muscles, and the blood, contain phosphate 



" The chemical reader, who is aware of the exact state of our knowledge upon this sub- 

 ject, will perceive that I speak here of the identity of these substances only in so far as the 

 proportions of carbon, hydrogen, oxygen, and nitrogen are concerned Ii is unnecessa-y to 

 allude in this place to the different proportions of sulphur and phosphonjs they are known 

 to contain— as the more popular nature of this work will not permit me to discuss the re- 

 fined, though singularly beautiful, physiological questions with which these differences arc 

 connected. 



