SECTION III. 



THE CHEMISTRY OF THE BLOOD, THE 



TISSUES AND SECRETIONS 



OF THE BODY. 



CHAPTER XL 



THE BLOOD. 



How Supplied. The conversion of food-stuffs into ab- 

 sorbable products has been discussed in the chapters of the last 

 section. It must be shown now how these products are util- 

 ized. Sooner or later, by absorption from the stomach or the 

 intestines, mainly from the latter organs, they enter the blood 

 stream through two principal channels, the portal vein and the 

 lacteal lymph vessels leading to the thoracic duct. Ordinarily 

 the amount of absorption from the walls of the stomach is not 

 great ; only when a very large quantity of easily digested food 

 is present in this organ or under the influence of special stim- 

 uli is the passage of digested substances into the circulation 

 here appreciable. The small intestine with its very consider- 

 able surface gives up the bulk of the absorbable products to 

 the blood or lymph stream. 



The digested fats pass essentially into the minute lymphatic 

 vessels known as the lacteals. At the time of digestion the 

 contents of these vessels is filled with a milky fluid termed 

 chyle, but at other times the lymph flowing here is nearly clear. 

 Minute capillary vessels leading to the portal vein take up the 

 larger portions of the carbohydrates and protein bodies from 

 the small intestine and thus convey them to the liver, where 

 a number of important changes take place, the most pro- 

 nounced being the conversion of the sugar more or less per- 

 fectly into glycogen. These reactions will receive attention 



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