892 PHYSIOLOGY 



owing to its low melting-point. In one experiment, when a cow 

 was fed on linseed oil, the iodine number of the milk fat C 

 30 its normal figure, to 704. After the introduction of iodine Z 

 subcutaneous* iodine fats are found m the milk. In anothe 

 experiment a bitch winch had been fed with mutton suet and 

 had Deposited in its tissues a fat of high melting point product 

 a milk the iodine number of which was the same as that of 

 the mutton suet. In this case the fat of the milk had evidently 

 been derived from the tissues, since during the lactation the anTnS 

 was being fed on meat which was poor in fat. The same dependent 



POS tin ofTh I ^ ha % been f Und m ^ eS6 ' Where ^ com- 

 tion of the oil secretion of the feather glands has been altered 



by giving abnormal fats, such as sesame oil, with the food 



to fal'i T C T U r ^ Pr tein f the f d cannot g> rise 



at m the body. A nearer consideration of the composition of the 



3 ms, taken m connection with our discussion as to the mechanism 

 ^ UP m ^ b0 ^' ^ to ~" 



Th 



re ch t'h 1 , rme y disinte ^tion of proteins 



chiefly the lower acids of the series, such as acetic and propionic 

 which would undergo rapid oxidation in the body. Butyric acid 

 has not yet been found among the products of Lnteg^t on o f 

 proteins, and the 6-carbon acid, derived from leucin, is not 

 the normal acid but is a branched chain, viz. isobutyl-aceiic acid 



chain of the 



fattv . e 



fatty acids might be built up, zxamely, butyric acid, is conspicuous 



by its absence and there is thus no starting-point among the 

 products o disintegration of the protein molecule which might serve 

 lor the synthesis of the fats of the body. 



THE UTILISATION OF FATS IN THE BODY 

 The constant presence of fat, and bodies allied to fat, in proto- 

 from whatever source obtained, suggests that these substances 

 can enter directly into the chemical changes on which the life of the 

 cell depends and that they play an essential part in vital phenomena. 

 The direct utilisation of fat for the needs of the body is also 

 indicated by the results of experiments on man and the lower animals. 

 After a few days starvation the body may be regarded as practically 

 free from stored carbohydrate. The sole source of the energy which 

 evolved under these circumstances must be fats and p;oteins 

 s- possible to determine by an estimation of the nitrogen 

 output the exact fraction of the total energy evolved which is to be 

 ascribed to protein metabolism. Thus in the case of Cetti the 

 professional faster, it was found that the nitrogenous metabolism 

 body weight remained fairly constant between the fifth 



