328 PHYSIOLOGY CHAP. 



on two young pigs of ten weeks, born in the same litter and of 

 equal weight. One was killed to determine the amount of fat 

 and nitrogenous substances contained in its whole body. The 

 second was kept alive four months, and constantly fed on barley, 

 which was chemically analysed. The total amount of fat and 

 nitrogenous substances were then estimated in this pig also, and 

 it was found that in four months, at most, 1560 grms. protein and 

 8560 grms. fat had been formed. Taking into account the whole 

 amount of protein and carbohydrate absorbed from the gastro- 

 intestinal canal, it was found that the animal had consumed 

 5930 grms. protein and had formed 7900 grms. new fat. Since 

 only the least part of this large amount of fat could derive from 

 the alimentary proteins consumed, it followed that the greater 

 part of it came from the carbohydrates. 



Another definite proof of the direct formation of fats from 

 carbohydrates was furnished by Meissl and Strohiner (1883), who 

 experimented on a pig one year old, which they fed for a week 

 on rice, with simultaneous estimations of the intake and output 

 of nitrogen and carbon. Other similar proofs were given by 

 Eubner (1886), who experimented on a dog fed after two days' 

 fast on cane sugar and starch. Thus not only herbivora but 

 carnivora also are able to form fat directly out of carbohydrates. 



From the chemical point of view as was remarked by Bunge 

 the formation of fat from carbohydrates is an enigma. The 

 fact is, however, well established experimentally, and is one of 

 the clearest examples that the cells of animal tissues are capable, 

 no less than those of plant tissues, of very complex synthetic 

 processes. 



XIII. We have seen that the synthetic reconstitution and 

 polymerisation of the principal digestive products of protein, the 

 proteases and peptones, is the function of the columnar epithelium 

 which lines the gastro-intestinal canal. These substances, therefore 

 (which are the true compensation products for the losses suffered by 

 the living protoplasm in the performance of its functions), penetrate 

 into the circulating fluids of the tissues in the same form as that 

 in which they are found in the plasma of the blood and lymph. 

 Although not experimentally demonstrated, it is highly probable 

 that the greater part, if not the whole, of the proteins introduced 

 with the food reach the circulation in the form of serum albumin. 



Owing to the marked tendency of the body to maintain the 

 constitution of the circulating fluids almost constant, the sum of 

 the protein absorbed after each meal does not accumulate in the 

 blood, but is at once stored up in the various tissues, where it 

 undergoes further transformations, either by forming more com- 

 plex syntheses and entering into the living protoplasm, or by 

 undergoing a series of retrograde changes in which the whole of 

 its potential energy is utilised under different forms by the body. 



