618 GENERAL METABOLISM [CII. XLI. 



blood for transportation. There is no loss of energy in this process 

 of fat-hydrolysis, any more than there is in the formation of lactic 

 acid from sugar ; or, to use the technical phrase, the reaction is an 

 isothermic one. 



Some observers have failed to discover lipase in the cells of the 

 tissues which contain fat. It is probable that here as in the 

 pancreas, lipase consists of two parts, an inactive component and an 

 activator (see p. 520). The failure to discover lipase is therefore 

 probably due to the circumstance that only the inactive portion is 

 present. It has been found that blood or blood-serum has no power 

 to split fats; it, however, does contain the activator of pancreatic 

 lipase. These facts justify the conclusion that the co-enzyme or 

 activator is a hormone produced in the pancreas, and carried by the 

 blood to the fat depots of the body, enabling the tissue lipase to 

 hydrolyse the fat carried to them by the blood-stream after digestion. 



The fat of the body may also arise from carbohydrate food. 

 This is a physiological fact which was first firmly established by 

 Lawes and Gilbert in their classical experiments on the fattening 

 of pigs sixty years ago. The transformation is a monopoly of 

 the living body : chemists were at first inclined to regard the fact as 

 fiction, and they have never been able to repeat it in the laboratory. 

 How the long carbon chains of the fat are linked together from the 

 shorter carbohydrate chains of sugar is at present a riddle. Micro- 

 organisms can accomplish the change of lactic acid into such fatty acids 

 as acetic, butyric, and caproic ; boiling with alkali brings about a similar 

 reaction ; and the same sort of change must occur in the body with 

 the formation of higher fatty acids. The liver appears to be the 

 place where the change occurs. 



May fats also arise from proteins? This is a controversial 

 question. Yoit and Pettenkofer said yes, because they were able to 

 fatten dogs on lean meat, but as the amount of fat left in the meat, 

 and the glycogen also present, were not taken into account, their 

 proof can hardly be considered satisfactory. The majority of physio- 

 logists to-day either answer the question in the negative, or regard it 

 as unproven one way or the other. They adopt this attitude because 

 the main proof adduced by those who believed in the transformation 

 of protein into fat has been shown to be fallacious. It was stated 

 that in certain pathological conditions, for instance in phosphorus 

 poisoning, a fatty degeneration of cells of certain organs takes place, 

 and the fat which appeared was believed to originate from the pro- 

 tein constituents of the cell-protoplasm. This is now known to be 

 incorrect ; every case of so-called fatty degeneration has been shown 

 to be either due to an infiltration of fat transported from elsewhere, or 

 to a transformation of the fat previously present in the protoplasm, 

 although not in the form of droplets, and probably also not in the 



