I7 6 THE VITAL PROCESSES 



by these it is emptied into the right auricle. This route 

 then includes the capillaries in the mucous membrane of the 

 stomach and intestines, the branches of the portal vein, 

 the portal vein proper, the liver, and the hepatic veins (Fig. 

 77). In passing through the liver, a large portion of the 

 food material is temporarily retained for a purpose and in a 

 manner to be described later (page 177). 



Absorption Changes. During digestion the insoluble 

 foods are converted into certain soluble materials, such as 

 peptones, maltose, and glycerine, the conversion being 

 necessary to their solution. A natural supposition is that 

 these materials enter and become a part of the blood, but 

 examination shows them to be absent from this liquid. 

 (See Composition of the Blood, page 30.) There are pres- 

 ent in the blood, however, substances closely related to the 

 peptones, maltose, glycerine, etc. ; substances which have 

 in fact been formed from them. During their transfer 

 from the food canal, the dissolved nutrients undergo 

 changes, giving rise to the materials in the blood. Thus are 

 the serum albumin and serum globulin of the blood derived 

 from the peptones and proteoses ; the dextrose, from the 

 maltose and other forms of sugar ; and the fat droplets, 

 from the glycerine, fatty acid, and soluble soap. 



While considerable doubt exists as to the cause of these 

 changes and as to the places also where some of them 

 occur, their purpose is quite apparent. The materials 

 forming the dissolved foods, although adapted to absorp- 

 tion, are not suited to the needs of the body, and if intro- 

 duced in this form are likely to interfere with its work. 1 

 They are changed, therefore, into the forms which the 

 body can use. 



1 Peptones and proteoses, when injected directly into the blood, are found to act 

 as poisons. 



