886 PHYSIOLOGY 



that this substance may play a part in the normal transformations 

 which occur within the cell, and may represent, so to speak, the 

 currency into which fat is transformed in order to participate in the 

 vital processes, and that it is in this form that the energy of fat is 

 utilised for the needs of the cell. 



ORIGIN OF FAT IN THE BODY 



Fat formation is the result of an excess of income over expenditure. 

 As soon as the latter exceeds the former the fat store is drawn upon, 

 so that 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 food-stuffs in the formation of 

 fat. Can this substance be formed from all three classes of food- 

 stuffs ? 



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 Lebedeff. Two 

 dogs, after a preliminary period of starvation, were fed, one on a 

 diet containing a large amount 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 adminis- 

 tration 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 only involve 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 



