CHAP, iv.] METABOLIC PROCESSES OF THE BODY. 811 



for the purpose of fattening, unless a sufficient proportion of 

 proteid material be given at the same time. 



The view however has been proved to be untenable by several 

 investigations carried out on different animals. It has been 

 shewn that an animal rapidly fattened on a diet consisting of 

 proteids with much carbohydrate will store up far more fat than 

 can possibly be accounted for by the proteids of the diet. Thus a 

 dog, the fat in whose body had been reduced to a minimum by 

 starvation, was fed for a period on measured quantities of proteids 

 and carbohydrates, and killed. The amount of fat found after 

 death in his body, making full allowance for the fat which 

 remained after the starvation and for the fat accompanying the 

 proteids in the meat given as food, was found to be far more than 

 could be supplied by the carbon in the proteids of the food, even 

 supposing that every jot of those proteids which did not go to 

 make up the increase of the proteid 'flesh' of the body taking 

 place during the fattening was used for the purpose of forming 

 fat. Similar experiments on geese and pigs have led to similar 

 results ; and if fat be formed in this way in the bodies of carnivora 

 and omnivora, we may be sure that the same holds good for the 

 bodies of herbivora. We may therefore conclude that fat can be 

 constructed in the body on the one hand out of proteid material, 

 and on the other hand by some direct conversion of carbo- 

 hydrates. 



508. It is clear then that a construction of fat does occur in 

 the body somewhere. What limits can we place on the degree to 

 which this construction is carried ? When the food contains 

 sufficient actual fat to account for the fat stored up in the body, 

 does any construction of fat take place ? In the first place we find 

 that when the food contains abnormal fats such as are not present 

 in the body, spermaceti for instance, or erucin (from rape-seed oil), 

 these fats are not to be found, or are found in very small quantity, 

 in the fat which is stored up in the body as a consequence of a 

 large supply of that food. In the second place we may call to 

 mind the statement previously made, that the composition of fat 

 varies in different animals. The fat of a man differs from the fat 

 of a dog, even if both feed on exactly the same food, fatty or other- 

 wise. Were the fat which is taken as food stored up as adipose 

 tissue directly and without change, recourse being had to other 

 sources of food for the construction of fat only in cases where the 

 fat in the food was deficient, we should expect to find that the 

 nature of the fat of the body would vary greatly with the food. 

 So far from this being the case, direct experiment shews that the 

 fat of the dog is, as far as composition is concerned, very largely 

 independent of the food, that the normal constituents of fat make 

 their appearance very much as usual and in very much their 

 appropriate proportion, though their proportion in the food may 

 largely vary, and though some of them may be wholly absent. 



522 



