CHEMISTRY OF THE FEEDING OF ANIMALS. 193 



it results that the amount of the nitrogen or ammonia-yielding 

 matter is practically the best index to the value of the manure. 



Appropriateness of Animal Food in the Diet of Man. 



It will be obvious that the importance of the subject which I 

 have brought before you this evening rests upon the assumption 

 that animal food is an important element in the diet of man. 

 There are, indeed, some who maintain that a purely vegetable 

 diet would be more suitable and natural than the mixed vegetable 

 and anim.al one so generally preferred. If their view were adopted 

 we need no longer trouble ourselves about the connection between 

 the food, the increase, and the manure of fattening oxen, sheep 

 and pigs. There are, however, various circumstances, economical 

 and physiological, pointing to the appropriateness of admitting a 

 certain proportion of animal food into the diet of man. To one or 

 two of these I will briefly refer. 



Walking is for man undoubtedly a very natural means of pro- 

 gression. Still, it is often very advantageous to ride, and so to 

 employ the legs of a quadruped instead of our own. In eating 

 meat Ave may be said to employ the stomachs of other animals to 

 do that which we could not so well do with our own. As a few 

 ounces of gold are separated from many tons of rock, by the com- 

 bined aid of mechanical and chemical processes, so the animals 

 feeding upon crude, and often to us indigestible, vegetable matter, 

 eliminate from it, and store up in their bodies some of its constit- 

 uents in a form at once much more concentrated than that in 

 which they consumed them, and much more easily appropriated 

 by the human economy. A given amount of nitrogenous com- 

 pounds in the form of meat is undoubtedly more easily digested 

 and assimilated by man than if the same amount were supplied in 

 the form of beans. Then, again, the animals convert starch, 

 sugar, &c., (and probably some of them cellulose, which we could 

 not digest at all) into fat, which has twice and a half the respira- 

 tory and fat-storing capacity of the substances from which they 

 produce it. It is, doubtless, true that man can produce fat, and 

 keep up his respiratory function from starch and sugar ; but it can 

 hardly be doubted that there is some economy to his system in 

 having a portion of fat supplied to him ready made. 



Apart from the strong testimony of common experience on the 

 subject, there is evidence in the comparative structure of man that 

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