5<>8 METABOLISM, NUTRITION AND DIETETICS 



that acetone forms a stage in the normal katabolism of the fatty 

 acids or of the /3-oxyacids derived from them. The importance of 

 the liver in the metabolism of fats is further indicated by the extent 

 of the migration of fat to that organ when the fat stores are mobilized 

 in unusual amount (p. 563). The reason for this migration seems 

 to be that the fats undergo preparatory changes which facilitate 

 their utilization by the tissues. For example, there is evidence 

 that saturated fatty acids are changed in the liver into unsaturated 

 acids, which are then carried to the organs to be metabolized. 

 The desaturation may serve the purpose of facilitating the rupture 

 of the long carbon chains, or their capacity for entering into reac- 

 tions with other substances, at the points where double links exist 

 between carbon atoms (p. 556). 



Non-Nutritive Functions of Fat. In connection with the metabo- 

 lism of fat, it ought to be noted that, in addition to their value as 

 reserve material for the nutrition of the body, the deposits of fat 

 under the skin and in other situations perform important functions 

 in protecting delicate structures from mechanical injury, in facili- 

 tating their movements upon each other, and in hindering the loss 

 of heat. It would doubtless be a gross exaggeration to say that the 

 mechanical and physical properties of the fat depots are as im- 

 portant in comparison to their chemical relations as is the case for 

 the bones and ligaments, but it would be an error not less gross to 

 consider them as of little account. It will even, perhaps, be 

 thought not unworthy of mention, from the point of view of the 

 propagation of the race, that in the human species, at least, the 

 amount and distribution of the cutaneous fat play a part of some 

 consequence in the aggregate of qualities which determine the 

 physical attractiveness of the individual, especially of the female, 

 although the standard in this regard varies widely in different 

 communities. 



It is perhaps partly because the fat depots have important 

 mechanical functions that the fat reserve is far less mobile than the 

 glycogen reserve. The semi-solid panniculus adiposus, the fatty 

 tissue around the great nerve trunks, between the muscles, around 

 the eyeball, on the soles of the feet, etc., possesses as a protective 

 packing the good qualities of a water cushion with none of its dis- 

 advantages. But if the fat-cells were subject to sudden depletion, as 

 the hepatic cells are nay, in still greater degree, since they contain 

 hardly any protoplasm they would never serve for such a function. 

 Of course, in the emergency of starvation, when even the glands 

 and the muscles themselves are wasting, the fat reserves are neces- 

 sarily mobilized, let their mechanical functions suffer as they may. 



Obesity. The proportion of the total mass of the body which is made 

 tip of fat varies greatly in different individuals, and often in the same 

 individual at different stages in life. When the accumulation of fat 



