NUTRITION. 473 



tion are due to a similar fatty degeneration in gland-cells. 

 Moreover, careful feeding experiments undoubtedly show that 

 fat can come from proteids; 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 conceiveably 

 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, 

 say olein, but a very slightly increased percentage of that 

 particular fatty substance is found in its adipose tissue, 

 which goes to show that if fats come from fats eaten, these 

 latter are first pulled to bits by the living cells and built up 

 again into the forms normal to the animal; so that, even with 

 fatty food, the fats stored up seem to be in most part manu- 

 factured in the Body. 



In still another way it is proved that fats can be con- 

 structed in the Body. In animals fed for slaughter, the total 

 fat stored up in them during the process is greatly in excess 

 of that taken with their food during the same time. For 

 example, a fattening pig may store up nearly five hundred 

 parts of fat for every hundred in its food, and this fat must be 

 made from proteids or carbohydrates. Whether it can come 

 from the latter is still perhaps an open question ; for, while 

 all fattening foods are rich in starch or similar bodies, there 

 are considerable chemical difficulties in supposing an origin 

 of fats from such; and it is on the whole more probable that 

 they simply act by sparing from use fats simultaneously 

 formed or stored in the body, and which would have other- 

 wise been called upon. They make glycogen, and this 



