METABOLISM 35 



logical explanation of the remark of an old nurse, quoted 

 by Lauder Brunton, that ' some fats are hard and some 

 soft, but cod-liver-oil fat is soon wasted.' It is probable, 

 however, that after its storage in the tissues fat is gradu- 

 ally worked up into a chemical form peculiar to the 

 human body. 



The functions of stored fat are stated to be two : 



(1) to serve as a reserve of energy-forming material, and 



(2) to dimmish heat loss. Of the reality of the first of 

 these alleged functions there can be no question, but it 

 may be asked, How large a fat reserve is it advisable to 

 harbour in the body ? There can be no doubt that in 

 the conditions of civilized life, with its regular three 

 meals a day, there is little advantage in the possession 

 of a large reserve of energy-forming material, although 

 in the case of a prolonged wasting disease such a reserve 

 must tend to lengthen the period during which a patient 

 can hold out. On the other hand, the presence in the 

 body of a large amount of fat has the obvious dis- 

 advantage that it increases the weight of the mass which 

 the muscles have to transport in locomotion, and in this 

 way must increase metabolic expenditure and restrict 

 activity. What the optimum amount of fat in the body 

 is we have no means of determining precisely.* It 

 probably corresponds to what is popularly known as the 

 ' fighting- weight ' that is to say, the weight at which 

 an individual is at his highest point of bodily strength 

 and endurance, and this appears to vary very much in 

 different persons. 



* In a well-nourished man fat makes up about 18 per cent, of 

 the body-weight. 



32 



