PRINCIPLES CONSUMED BY THE OPvGANISM. 501 



has been impossible thus far to determine. We must be content to say that the exact 

 changes which the sugars undergo in nutrition are unknown. They seem to be very 

 important in development, being abundant in the food and formed largely in the system 

 in early life. They certainly do not enter into the composition of the tissues; and it 

 would seem that they must be important in the two remaining phenomena of nutrition, 

 namely, the formation of fat and the development of animal heat. The relations of sugar 

 to these two processes will be taken up under their appropriate heads. 



The fats taken as food are either consumed in the organism or are deposited in the 

 form of adipose tissue. That the fats are consumed, there can be no doubt; for, in the 

 normal alimentation of man, fat is a constant article, and it is never discharged from the 

 body. We are forced to admit, however, that the changes which fat undergoes in its 

 process of destruction are not thoroughly understood. All that we positively know is, 

 that the fatty principles of the food are formed into a fine emulsion in the small intestine, 

 and are taken up, chiefly by the lacteals, and discharged into the venous system. For a 

 time, during absorption, fat may exist in certain quantity in the blood ; but it soon disap- 

 pears and is either destroyed directly in the circulatory system or is deposited in the 

 form of adipose tissue to supply a certain amount of this substance consumed. That it 

 may be destroyed directly is proven by the consumption of fat in instances where the 

 amount of adipose matter is insignificant ; and that the adipose tissue of the organism 

 may be consumed is shown by its rapid disappearance in starvation. 



The question of the relations of fat to nutrition is important but somewhat obscure. 

 It does not take part in the nutrition of the parts that are endowed to an eminent 

 degree with the so-called vital functions ; and, when these tissues are brought to their 

 highest point of development, the fat is entirely removed from their substance. If 

 fat be not a plastic material, it would seem to have no function remaining but that of 

 keeping up, by its oxidation, the animal temperature. But it is not proven that the fats, or 

 fats and sugar, are the sole principles concerned in the production of carbonic acid and 

 the generation of heat; for both of these phenomena occur in the carnivora, and in man, 

 when fat and sugar are eliminated from the food and the fat in the body has been 

 reduced to the minimum. Fat is undoubtedly destroyed in the organism, and probably 

 it assists in the formation of the carbonic acid eliminated ; it is also taken in much larger 

 proportion in cold than in temperate or warm climates; but we cannot, with our present 

 information, say without reserve that fats and sugar are oxidized directly, by a process 

 with which we are familiar under the name of combustion, and that their exclusive func- 

 tion is the production of animal heat. 



It is a curious fact that fat is generally deposited in tissues during their retrograde 

 processes. The muscular fibres of the uterus, during the involution of this organ after 

 parturition, become the seat of a deposit of fatty granulations. Long disuse of any part 

 will produce such changes in its power of appropriating nitrogenized matter for its regen- 

 eration, 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 it takes the place of the substance that gives to the part its char- 

 acteristic functions. These phenomena are strikingly apparent in muscles that have been 

 long disused or paralyzed and 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, with appropriate exercise ; but frequently the alteration has 

 proceeded so far as to be irremediable and permanent. 



Accurate observations have shown that, in young animals 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 econo- 

 my is one of great importance. Whatever the exact nature of the changes accompanying 



