200 INTERMEDIATE METABOLISM 



depots. This is proved by the following experiment. Two 

 dogs are fed, one of them on an ordinary diet, the other 

 on hnseed oil. On poisoning them with phosphorus the 

 hver fat is fomid to be composed, in the former, of ordinary 

 dep^t fat of the dog; in the latter, of hnseed oil. The 

 origin of the hver fat is therefore from the intestine and 

 from the depots. Arrived at the liver, the fat undergoes 

 two changes : double linkages are introduced {desaturation), 

 whether the fatty acids were previously saturated or 

 unsaturated. Thus there are formed fatty acids still more 

 unsaturated than oleic acid. The other change consists 

 in the building wp of the fat into lecithin, indicated by the 

 fall in the proportion of fatty acid. 



In other words, the hver converts the fat from the 

 form in which it exists in the food and in the depots into 

 the form in which it exists in the living cell. From this 

 it would appear that the hver prepares the fat for use 

 in the tissues, fat being more easily burnt after being 

 desaturated. The process of desaturation also occurs in the 

 tissues in general, but to a less extent than in the liver. 



Formation of Fat from Carbohydrate 



Though the conversion of carbohydrate into fat in the 

 body must have been beheved in for centuries, it was not 

 until 1852 that it was actually proved. In that year 

 Laives and Gilbert took two pigs of similar size and weight 

 from the same htter. One they killed, and estimated the 

 fat, protein and carbohydrate content of its body. The 

 other they fed on a diet of known composition. After a 

 few months this pig was killed and analysed. The amount 

 of fat present in this animal over and above that which 

 was present in the animal killed earher was found to be 

 far in excess of the maximum which could theoretically 

 have been derived from the fat and protein of the food. 



A second proof of the conversion of carbohydrate into fat 

 is alleged from the study of the respiratory quotient. In 

 the early stage of hibernation the respiratory quotient 



