ABSORPTION 351 



A. Storage of Surplus Food. 



1, Fat. — Since, bulk for bulk, fat has more than twice the 

 energy value of proteins or carbohydrates (p. 257), it is an 

 advantage to store surplus food as Fat. In fat oxen or sheep 

 the fat may constitute nearly 50 per cent, of the weight 

 of the carcase. This stored fat is not immediately available. 

 It may be regarded as invested capital which has to be 

 placed at current account before it can be used. 



This storage takes place chiefly in three situations : (1) 

 Fatty tissue ; (2) Muscle ; (3) Liver. 



(1) In Fatty Tissue. — In most mammals the chief storage 

 of surplus food is in the fatty tissues. 



(a) That the fat of the food can be stored in them is 

 shown by the fact that the administration of large amounts 

 of fats, different from those of the body, leads to their 

 appearance in those tissues. The administration of erucic 

 acid to dogs leads to its appearance in the fat, and cows fed 

 on maize oil yield butter of a low melting-point. Fats 

 stained with Sudan III. carry the stain into the fatty tissue in 

 which they are deposited. 



(b) That fat is formed from carbohydrates was proved by 

 Laws and Gilbert in the feeding of young pigs. Two of 

 a litter were taken and one was killed and analysed. The 

 other was fed for weeks upon maize, the amount eaten being 

 weighed, and the excretion of nitrogen by the pig being 

 determined. The animal was then killed and analysed, and 

 it was found that the fat gained was more than could be 

 accounted for by the fat and protein of the food eaten. 



In this process of fat formation the respiratory quotient 

 may rise above I'O. It is probably carried out as follows: — 



6 CsHiA + 13 Go = 20 CO2 + C16H3A + 20 H.O 



Glucose. Fatty Acid. 



The greater energy of the fatty acid molecule as compared 

 with that of the sugar is got by the oxidation of some of the 

 susrar alons? with a reduction of the rest. 



(c) The evidence that fats may be formed from the 

 proteins of the food is conflicting. (1) In the ripening of 



