THE METABOLISM OF THE BODY. Ml 



as dry proteid. It is perfectly plain, then, that proteid diet 

 does not involve only proteid construction within the body. 



Comparative. — The amount of flesh which a dog, being a 

 carnivorous animal, can digest and use for the maintenance of 

 his metabolic processes is enormous ; though it has been learned 

 that ill-nourished dogs can not even at the outset of a feeding 

 experiment of this kind maintain the equilibrium of their body 

 weight on a purely flesh diet (fat being excluded). They at 

 once commence to lose weight — i. e., they draw upon their own 

 limited store of fat. 



The digestion of herbivora being essentially adapted to a 

 vegetable diet, they can not live at all upon flesh, while a dog 

 can consume for a time without manifest harm ^'5 to ^ of its 

 body-weight of this food. 



Man, when fed exclusively on meat soon shows failure, he 

 being imable to digest enough to supply the needed carbohy- 

 drates, etc. But the large amount of urea in the urine of car- 

 nivorous animals generally, and the excess found in the urine 

 of man when feeding largely on a flesh diet, show that the pro- 

 teid metabolism is under such circumstances very active. 



It is also a well-known observation that carnivorous ani- 

 mals (dogs) are more active and display to a greater extent 

 their latent ferocity, evidence of their descent from wild car- 

 nivorous progenitors, when like them they feed very largely on 

 flesh. The evidence seems to point pretty clearly to the con- 

 clusion that a nitrogenous (flesh) diet increases the activity of 

 the vital processs of the body, and especially the proteid me- 

 tabolism. 



But in all these considerations it must be borne in mind that 

 the metabolic processes go on in the tissues and not in the 

 blood, and probably not in the lymph. Not that these fluids 

 (tissues) are without their own metabolic processes for and by 

 themselves; but what is meant to be conveyed is that the met- 

 abolic processes of the body generally do not take place in the 

 blood. 



The Effects of Gelatin in the Diet— Actual experiment shows 

 that this substance can not take the place of proteid, though it 

 also makes it evident that less of the latter sufiices when mixed 

 with a certain proportion of gelatin. It will be borne in mind 

 that ordinary flesh contains, as we find it naturally in the car- 

 cass, not only some fat, but a good deal of fibrous tissue, which 

 can be converted by heating into gelatin. 



