METHODS OF ABSORPTION. 205 



some unstriated muscle cells which embrace the villus and are 

 able to squeeze it and empty the vessel it contains. 



The lacteal radicles which lie in the villi are sometimes double, 

 and have a communication with the lymph spaces of the connec- 

 tive tissue. They frequently branch as they pass down from the 

 villi to reach the dense network of lacteal vessels which lies be- 

 neath the mucous membrane. At irregular intervals throughout 

 the submucous tissue are found masses of lymphoid tissue similar 

 to that seen in packets within a lymph gland or in other lymph 

 follicles. These are either isolated (solitary glands) or collected 

 into groups (agrainated or Peyer's glands). Though called glands 

 by anatomists, it should be borne in mind that they are in no 

 way connected with the secretion of any of the intestinal juices, 

 but belong to the absorbing arrangements of the intestine. 

 Around these solitary and grouped lymph follicles are spaces 

 and networks from which the lacteal vessels arise (Fig. 93). 



MECHANISM OF ABSORPTION. 



Formerly, absorption was supposed to take place by means of 

 the blood vessels alone, but after the discovery of lymph and 

 chyle vessels by Caspar Asellius the belief in the direct absorp- 

 tion by the blood vessels was completely abandoned, and all the 

 work of absorption was attributed to the lymphatics. However, 

 ample evidence exists to show that substances capable of absorp- 

 tion can make their way into the blood vessels of any part not 

 protected by an impermeable covering like the horny layer of 

 the skin, and thus be carried directly to the general circulation. 

 The share taken by the blood vessels in interstitial absorption in 

 the tissues is not defined, and when no empediment to the lymph 

 flow exists is probably very small. 



In the absorption from the alimentary tract, however, the 

 blood vessels appear to take a considerable part. 



How far the tissue interspaces and the local lymph channels, 

 many of which surround the blood vessels, aid in the passage of 

 substances into the blood currents, is not known ; but most likely 

 they have some such effect, for the experiments showing direct 

 absorption by the blood vessels leave the local lymph channels in 



