THE ABSORPTION AND USE OF FOODS 515 



as well as upon general metabolism this treatment should never 

 be undertaken except under competent medical advice. 



Source of the Body Fat. For a long time there was much dis- 

 cussion as to which of the three sorts of food stuffs, proteins, car- 

 bohydrates, or fats, is the source of the fat which is stored in the 

 Body. The natural conclusion that body fat is derived from food 

 fat is shown to be not universally true, at any rate, by the ability 

 of cattle to produce milk, with its abundant fat content, upon a 

 diet of hay and grain in which no trace of fat occurs. The ques- 

 tion whether in these animals the protein or the carbohydrate of 

 the food gives rise to the fat was formerly much studied ; but with 

 the rise of the modern view of normal protein metabolism, accord- 

 ing to which all but a small percentage of the protein taken in the 

 food is deaminized and used as carbohydrate, the question has 

 lost much of its force. There can be little doubt that body fat 

 represents stored fuel/ and since the whole fuel supply of the 

 bovine Body is often represented by carbohydrates, these must 

 be the source of the fat which the Body elaborates. 



It seems to be the general opinion that even in animals whose 

 diet includes some fat the normal source of the body fat is for the 

 most part carbohydrate. It is supposed, without very definite 

 evidence to prove it, that the fat absorbed after a meal is retained 

 in the blood till taken up by the tissues and burned, and that the 

 somewhat leisurely process of fat deposition is carried on in con- 

 nection with the carbohydrate, which is transferred from its 

 temporary storehouse in the liver to a more permanent one in 

 the adipose tissues. There is no reason to doubt that when large 

 amounts of fat are included in the diet there may be direct storage 

 of some of the fat absorbed. In fact it has been shown that under 

 these circumstances foreign fats, such as linseed-oil, for example, 

 can be deposited in the adipose tissues of animals. 



