30 WILDEE TILESTON 



iodin number are fed, the fat in the chyle is found to have a much lower 

 melting point and higher iodin number, and vice versa. This is accom- 

 plished by the addition of oleic acid in the former case and of fats with a 

 high melting point in the other. Under unusual conditions, however, such 

 as when large amounts of foreign fat are fed to a starving animal, the fat 

 may be deposited unchanged, as shown by Munk and others in experiments 

 with mutton fat, linseed oil, etc. 



That carbohydrate may be converted into fat is a well known fact, 

 which has been proved by feeding experiments. The situation where this 

 change takes place is not yet known. An interesting effect of such con- 

 version on a large scale is the raising of the respiratory quotient, which 

 may go well above unity under exceptional conditions, as in marmots 

 just before hibernation (Pembrey). This is due to the conversion of a 

 substance rich in oxygen to one poor in that element, with the giving off 

 of CO 2 . 



Protein may serve as a source of fat, as has been shown by feeding 

 experiments in which large amounts of meat were given. This probably 

 results from the conversion of the carbohydrate portion of the protein 

 molecule to fat. To what extent this takes place under ordinary con- 

 ditions has not been ascertained. 



The bulk of the fat of the tissues is ordinarily derived from carbo- 

 hydrate, which usually furnishes two-thirds of the energy derived from 

 the food. Fat comes next, while protein provides only a negligible 

 quantity. 



Fat is deposited in health chiefly in the subcutaneous tissues, to a 

 lesser degree about the abdominal viscera, serving as a padding to keep 

 the organs in place. In obese subjects it is also largely deposited in the 

 abdominal cavity, about the viscera and in the omentum and mesentery 

 and retroperitoneal tissues, also about the heart, which may show a 

 marked degree of fatty infiltration. 



Fat is not ordinarily deposited in the liver to any great extent, the 

 fat content of the normal liver being six per cent. In starvation and 

 cachexia, however, the amount rises considerably. There is an antagonism 

 between glycogen and fat deposit, for if carbohydrates and fat be given 

 together to a starving animal, the liver fat does not increase, but glycogen 

 is retained, while in obesity, on the other hand, the fat content may be in- 

 creased to a certain extent, at the expense of the glycogen, as indicated 

 by the researches of Means. 



Following, the law of the conservation of energy, foodstuffs must be 

 stored in the body whenever the amount of energy introduced with the 

 food, as expressed in calories, is in excess of the energy consumed. Since 

 the ability of the body to store carbohydrate and protein as such is 

 limited, an accumulation of fat is bound to occur if the excess of income 

 over outgo is long continued. This disproportion may be due either to 



