828 PHYSIOLOGY 



adipose tissue is the one which presents the greatest loss during starvation. 

 As much as 97 per cent, of the total fat of the body may disappear during 

 this process. We have therefore to consider what part is played by each 

 class of foodstuffs in the formation of fat. Can this substance be formed 

 from all three classes of foodstuffs? 



FORMATION FROM THE FAT OF THE FOOD. Experiment has 

 shown that the composition of the fat of any animal is by no means constant 

 and can be varied within wide limits by alterations in the nature of the 

 fat presented in the food. This dependence of the composition of the fat 

 on the fats of the food is shown strikingly in an experiment performed by 

 LebedefL Two dogs, after a preliminary period of starvation, were fed, 

 one on a diet containing a large proportion of linseed oil, and the other on 

 a diet containing much mutton suet. After some weeks, when the animals 

 had put on a large amount of fat, they were killed, and it was found that 

 whereas- the fat of the dog which had been fed on mutton suet was solid 

 at 50 C., that of the dog fed on oil was still fluid at C. It has been 

 shown moreover that, by feeding animals with fatty acids not usually found 

 in the body, these are laid down in the adipose tissue. Thus colza oil 

 contains a glyceride of erucic acid, and an animal, as Munk has shown, 

 fed on colza oil lays on fat in which erucic acid is present. The same 

 physiologist has observed that, after the administration of various fatty 

 acids to a man with a chylous fistula, the glycerides of the corresponding 

 fatty acids made their appearance in the chyle, whether these fatty acids 

 were those normal to man or consisted of substances, such as erucic acid, 

 not generally found in human fat. One must conclude therefore that the 

 fats taken with the food, if not immediately required for the energy needs 

 of the body, are laid down without change in the adipose tissues, as well 

 as in the cells of the body. The mechanisms involved in the translation of 

 fat from the alimentary canal to the tissues are of the simplest possible 

 description and involve only changes of hydrolysis and dehydrolysis. The 

 fats are hydrolysed in the gut and are resynthetised to a certain extent 

 in their passage into the epithelium. In the chyle and blood they probably 

 wander chiefly as neutral fats, to be rehydrolysed for their passage into 

 the cells of the body, which they may enter either in the form of soaps or 

 possibly as fatty acids dissolved in some of the constituents of protoplasm. 

 FORMATION OF FAT FROM CARBOHYDRATES. It has long been 

 the experience of farmers that animals might be fattened on a diet in which 

 carbohydrates predominate. The chemical difficulty involved in the trans- 

 formation of carbohydrates into fats has often led to a doubting attitude 

 on the part of chemists towards this transformation. Voit put forward 

 the view that, when fats are formed in the body as a result of an excessive 

 carbohydrate diet, they are formed, not directly by a transformation of 

 carbohydrate, but from the proteins of the food, the role of the carbohydrates 

 of the food being simply to protect the proteins from disintegration and 

 oxidation, so that the whole of their carbon can be utilised for the 

 formation of fat. 



