ABSORPTION BY LACTEAL AND LYMPHATIC VESSELS. 273 



In the passage of the food along the intestinal canal, as the digestion of 

 the albuminoids is completed, these matters are absorbed, and their passage 

 into the mass of blood is indicated by an increase in its proportion of albu- 

 minoid constituents. The greatest part of the food is absorbed by the intes- 

 tinal mucous membrane, and with the alimentary substances proper, a large 

 quantity of secreted fluid is reabsorbed. This fact is particularly marked as 

 regards the bile. The biliary salts disappear as the alimentary mass passes 

 down the intestine, and undoubtedly are absorbed, although they are so 

 changed that they can not be detected in the blood by the ordinary tests. 

 In this portion of the alimentary canal, it will be remembered, an immense 

 absorbing surface is provided by the arrangement of the mucous membrane 

 in folds, forming the valvulae conniventes, and by the presence of villi, which 

 are found throughout the small intestine. A certain portion of the gaseous 

 contents of the intestines is also taken up, although it is not easily ascer- 

 tained what particular gases are thus absorbed. 



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 six- 

 teenth century, by Eustachius, and finally to the discovery of the lacteals by 

 Asellius, in 1622, is more interesting in an anatomical than in a physiologi- 

 cal point of view. The history of the anatomy of the absorbent system dates 

 from the discovery of the thoracic duct ; but from the discovery of the lac- 

 teals, by Asellius, dates the history of these vessels as the carriers of nutritive 

 matters from the intestinal canal to the general system. 



In 1649, Pecquet discovered the receptaculum chyli and demonstrated 

 that the lacteals did not pass to the liver, but emptied the chyle into the 

 thoracic duct, by which it is finally conveyed into the venous system. In 

 1650-'51, the anatomical history of the absorbent vessels was completed by 

 the discovery, by Rudbeck, of vessels carrying a colorless fluid, in the liver 

 and finally in almost all parts of the body. Eudbeck demonstrated the ana- 

 tomical identity of these vessels with the lacteals. They were afterward 

 studied by Bartholinus, who gave them the name of lymphatics. 



The idea, which dates from the discoveries of Asellius and Pecquet, that 

 the lacteals absorb all the products of digestion, was disproven by the exper- 

 iments of Magendie and of those who experimented after him upon vascu- 

 lar absorption. It is now known that fats in the form of a very fine emul- 

 sion are absorbed by the lacteals, and that these are the only constituents of 

 food taken up in great quantity by this system of vessels. It becomes an 

 important question to determine, however, whether the lacteals be not con- 

 cerned, to some extent, in the absorption of drinks, the albuminoids, saline 

 and saccharine matters, etc, This question will be taken up after a consid- 

 eration of certain points in the anatomy of the lymphatic system. 



Physiological Anatomy of the Lacteal and Lymphatic Vessels. The 

 lacteals are the intestinal lymphatics ; and during the intervals of intestinal 



