444 THE HUMAN BODY. 



require some time, before it can be taken into the blood 

 and carried off to other parts. 



When adipose tissue is developing it is seen that undif- 

 ferentiated cells in the connective tissues (especially areolar) 

 show minute oil-drops in their protoplasm. These increase 

 in. size and, ultimately, fuse together and form one larger 

 oil-droplet, while most of the original protoplasm dis- 

 appears. 



The oily matter would thus seem due to a chemical 

 metamorphosis of the cell protoplasm, during which it gives 

 rise to a non-azotized fatty residue which remains behind, 

 and a highly nitrogenous part which is carried off. In 

 many parts of the Body protoplasmic masses are subject to 

 a similar but less complete metamorphosis; fatty degenera- 

 tion of the heart, for example, is a more or less extensive 

 replacement of the proper substance of its muscular fibres 

 by fat-droplets; and the cream of milk and the oily matter 

 of the sebaceous secretion are due to a similar fatty 

 degeneration in gland-cells. Moreover, careful feeding ex- 

 periments undoubtedly show that fat can come from pro- 

 teids; when an animal is very richly supplied with these 

 all the nitrogen taken in them reappears in its excretions, 

 but all the carbon does not; it is in part stored in the Body: 

 and, since such feeding produces but little glycogen, this 

 carbon can only be stored as fat. 



While there is, then, no doubt that some fat may have a 

 proteid origin, it is not certain that all has such. During 

 digestion a great deal of fat is ordinarily absorbed, in a 

 chemically unchanged state, from the alimentary canal; it 

 is merely emulsified and carried off in minute drops by the 

 chyle to be poured into the blood: and this fat might be 

 directly deposited, as such, in adipose tissue. There are, 

 however, good reasons for supposing that all the fat in the 

 Body is manufactured. The fat of a man, of a dog, and of a 

 cat varies in the proportions of palmatin, stearin, margarin, 

 and olein in it; and varies in just the same way if all be fed on 

 the same kind of food, which could not be the case if the 

 fat eaten were simply deposited unchanged. Moreover, if 

 an animal be fed on a diet containing one kind of fat only, 



