422 ABSORPTION. 



floor, was white, like milk. We have since frequently at- 

 tempted to demonstrate this excessively chylous condition 

 of the blood during the absorption of fats, but have found 

 that it is not generally so well marked. 



The greatest part of the food is absorbed by the intesti- 

 nal mucous membrane, and, with the alimentary substances 

 proper, a large quantity of secreted fluid is reabsorbed. This 

 fact is particularly striking as regards the bile. The biliary 

 salts disappear as the alimentary mass passes down the intes- 

 tine and are undoubtedly absorbed, though they are so 

 changed that they cannot be detected in the blood by the 

 ordinary tests. In this portion of the alimentary canal, it 

 will be remembered that an immense absorbing surface is 



O 



provided, by the arrangement of the mucous membrane in 

 folds, forming the valvulso conniventes, and the presence of 

 the innumerable villi which are found throughout the small 

 intestine. A certain portion of the gaseous contents of the 

 intestines is also absorbed, though it is not easily ascertained 

 what particular gases are thus taken up. 1 



Absorption by Lacteal and Lymphatic Vessels. 



The history of the discovery of what is ordinarily termed 

 the absorbent system of vessels, from the vague allusions of 

 Hippocrates, Galen, Aristotle, and others, to the description 

 of the thoracic duct in the middle of the sixteenth century 

 by Eustachius, 2 and finally to the discovery of the lacteals 

 by Asellius, in 1622, is more interesting in an anatomical, 



1 In treating of digestion, we have necessarily considered the complete prepara- 

 tion of alimentary principles for absorption, and have frequently alluded to the 

 fact that these principles are taken up as fast as they are thus modified. In con- 

 nection with the subject of absorption, therefore, it will be only necessary to point 

 out the vessels which are concerned in this function, and the mechanism of the 

 passage of liquids through their walls. 



2 BARTHOLOMEWS EUSTACHIUS, De Vena quce Azygos Greeds dicilur, etc. ( Opus- 

 <wla Anatomica, Yenetiis, 1564, p. 301). Eustachius discovered in the horse a ves- 

 sel beginning at the left jugular vein and descending toward the pillars of the 

 diaphragm, which he described as " always white, and filled with watery humor." 

 This was the thoracic duct. 



