20G W. II. BLOOR 



in more than small amounts in active tissues such as the heart, kidney and 

 muscles, although considerable lipoid material of other kinds is present 

 there. The stored fat has its origin in part directly from the fat of the 

 food and in part indirectly by synthesis from other food substances, mainly 

 carbohydrate. Synthesis from protein probably does not ordinarily take 

 place to any considerable extent. Under certain circumstances stuffing 

 of an animal with fat, especially after starvation food fat may be laid 

 down in the fat depots with but little if any change, but under ordinary 

 conditions where the animal has a normal choice of food there is a marked 

 tendency to produce a fat characteristic of the animal ; for example, beef 

 fat has certain definite characteristics which distinguish it from hog fat and 

 both from human fat. The laying down of a characteristic body fat by 

 an animal from its food must involve several factors such as choice from 

 the food fat as to which portion is to be immediately consumed and which 

 stored, the nature of the fat. synthesized from carbohydrate, also, in case 

 the stored fat is used, choice as to whether the harder or softer constituents 

 are to be used first, since there is some evidence to show that the fat of a 

 starved animal has a higher melting point than the normal body fat of 

 the animal. Although the laying up of a characteristic fat is partly the 

 resultant of these factors, their activity is limited and in the end the fat 

 stored is greatly influenced by the food fat especially if it forms a large 

 proportion of the diet. The question has a considerable economic interest 

 in connection with the fattening of animals, e. g., hogs for market, since 

 it has been found that if too much liquid fat is inclndcd in the diet the 

 result is a soft meat from which the fat oozes out on standing; 



Changes in Fat in the Tissues. If the stored fat is thus markedly 

 influenced by the food fat, the built in fat or cell lipoitl is just as notably 

 characteristic of the tissue and uninfluenced by the food fat, and since the 

 fatty acids found in combination in the cell lipoids are often different 

 from those ordinarily found in the food, the question arises as to the power 

 of the tissues to alter for various purposes the fat presented to them. 

 The differences between the fatty acids of the active tissues and those of 

 the food consist mainly in (a) their degree of saturation, (b) the groups 

 with which they are combined. They are in general much more un- 

 saturated, the iodin absorption value of the fatty acids of the tissues is 

 found to be in the neighborhood of 130, while that &f the stored fat is 

 from 35 to 70. The* iodin value of the blood lipou!$ in normal human 

 beings is about 66 (calculated). The fatty acids in foe tissue cells are 

 largely combined as phospholipoids, although there an? also a number of 

 other combinations of the fatty acids to be found in the -organs and in the 

 brain and nervous tissue. These, with few exceptions, are not well 

 understood chemically, and since they apparently take taut a small part in 

 ordinary fat metabolism they will not he considered luere. The presence 

 of .compounds of the unsaturated fatty acids, especially jsiiospholipoids, in 



