THE METABOLISM OF FAT 441 



In man, during starvation, respiratory quotients below 0-7 have 

 also been observed, and it is quite possible that, under these circum- 

 stances, some fat is being converted into carbohydrates, and meta- 

 bolized in that manner. 



The Metabolism of Lecithin. Lecithins are found in all the tissues 

 of the body, partly free, partly combined with protein. Entering 

 largely into the composition of the cell membrane, they are supposed 

 to control the passage of bodies into the cell, in addition to playing 

 an important part in the chemical processes of the cell. The amount 

 of lecithin is diminished in the body by starvation, and also by 

 wasting diseases and phosphorus -poisoning. 



Anabolism. The various lecithins are probably continuously 

 being formed in the organism. From experiments made by feeding 

 with foreign fats, it is found that such e.g., linseed oil are not 

 built-up into the lecithins of the body. That lecithin is formed in 

 the organism is shown by the fact that mice fed on a lecithin-free 

 diet grew well, and brought forth young. It is possible that each 

 animal has its own characteristic lecithin, and that the fatty acid 

 molecules of these are developed from the carbohydrate of the diet, 

 and not from the fat. Lecithin is formed in green leaves exposed 

 to light. 



Katabolism. When lecithin breaks down, it forms first of all 

 glycerophosphoric acid and cholin, and subsequently glycerine, 

 phosphoric acid, and fatty acid. The phosphoric acid is probably 

 excreted in the urine as phosphates, and the other bodies burnt up 

 in the organism. Under certain circumstances, the lecithin and its 

 derivatives may be deposited in the cell as oily droplets, giving a 

 condition similar to that known as " fatty degeneration." 



Fatty Degeneration. In certain diseases, and after the application 

 of experimental methods, such as phosphorus-poisoning, the cells 

 of certain organs show on microscopic examination the presence of 

 fatty droplets within the cell. The .nucleus of the cell may or may 

 not be fragmented. Such a condition has been termed " fatty de- 

 generation." Much experimental work has been done to prove the 

 origin of this fat, and also the circumstances which bring about the 

 condition. In regard to the latter point, one of the chief causes is 

 a diminished alkalinity of the cell fluid. Fatty degeneration takes 

 place in dying cells. 



In regard to the source of the fatty droplets, the chief views held 

 are these: 



1 . That the fat is essentially an infiltration into the cells from the 

 fat depots of the body. 



2. That the fat is the " masked " fat of the cell which has become 

 " revealed " in droplet form e.g., that the fat is fat which was linked 

 to protein, and has become dissociated and visible. 



3. That the fat has been formed from carbohydrates of the cell, 

 or from ammo-acids produced as the result of the autolysis of the 

 cell proteins. 



