382 NUTRITION. 



Long disuse of any part will produce such changes in its 

 power of appropriating nitrogenized matter for its regenera- 

 tion, that it soon becomes atrophied and altered. Instead 

 of the normal nitrogenized elements of the tissue, we have, 

 under these circumstances, a deposition of fatty matter. 

 The fat is here inert, and takes the place of the substance 

 that gives to the part its characteristic function. These phe- 

 nomena are strikingly apparent in muscles that have been 

 long disused or paralyzed, or in nerves that have lost their 

 functional activity. If the change be not too extensive, the 

 fat may be made to disappear, and the part will return to its 

 normal constitution, by appropriate exercise ; but frequently 

 the alteration has proceeded so far as to be irremediable and 

 permanent. This condition is known in pathology under 

 the name of fatty degeneration a term which implies that 

 the nitrogenized elements of the part are changed or degen- 

 erated into fat, and which is not strictly correct. During the 

 ordinary process of nutrition, the nitrogenized elements are 

 removed by disassimilation, and new matter, of the same 

 kind, is deposited ; but when the so-called fatty degenera- 

 tion ocures, fat is substituted for the nitrogenized substance. 

 This change, then, should rather be called fatty substitution. 1 

 Accurate observations have shown that, in young ani- 

 mals, rapidly fattened, all the adipose matter in the body 

 cannot be accounted for by what is taken in as food ; and it 

 is certain that fat may be produced de novo in the organism. 



Formation and Deposition of Fat. The question of the 

 generation of fat in the economy is one of great importance. 

 Whatever the exact nature of the changes accompanying 

 the destruction of non-nitrogenized matter may be, it is 

 certain that the fat stored up in the body is consumed, 

 when there is a deficiency in any of the elements of food, as 

 well as that which is taken into the alimentary canal. It is 



1 LITTRK ET ROBIN, Dictionnaire de medecine, Paris, 1865, p. 1444, Article, 

 Substitution graisseusc. 



