THE STORY OF DIGESTION 45 



small; if small, however, it must be regarded as 

 nevertheless of high importance. It is not denied 

 that a certain minor action on non-nitrogenous 

 starches and sugars may be exerted by the stomach, 

 but the all-important part of its work is the action 

 which it exerts on nitrogenous articles of diet. 



PEPTONES. The gastric juice thoroughly mixed 

 with the food, and leaving practically unaltered the 

 sugar contained in the food and any starch which 

 may have escaped the action of the saliva of the 

 mouth exerts its power, as we have seen, on nitro- 

 genous articles of diet. Coming in contact with 

 albumen or any other foods of this class it converts 

 them into bodies known as "peptones." One of the 

 chief differences between a peptone and the food it 

 previously represented is that, as a peptone, it can 

 easily pass through the walls of the stomach and 

 be absorbed by the bloodvessels. The peptone 

 possesses other characteristics, but this last is the 

 special feature to which attention may here be 

 directed. The result is that the peptones leave the 

 stomach and pass as described into the bloodvessels 

 of the organ. They then find themselves in the 

 veins of the stomach which join a very large vessel 

 known as the " portal vein," returning blood from 

 the whole of the digestive organs. In tracing 

 the course of the portal vein we find that it dis- 

 appears into the liver, so that the liver is the direct 

 destination of the peptones which it has been the 

 business of the stomach to separate out from the 

 rest of the food; these peptones, as we have seen, 

 representing the changed nitrogenous articles of 

 diet which have been consumed* What happens to 

 the peptones in the liver will hereafter be described, 

 but it should be noted that already from the stomach 



