INTESTINAL ABSORPTION. 157 



fluid parts of the corpuscle are entangled acts as a membrane 

 would, and while a certain amount of fluid passes out, a 

 larger amount of water passes in and gorges the corpuscle. 

 So also nucleated cells, when water is added to them, become 

 rapidly swollen, till they burst and are destroyed. 



Now, there seems no reason to doubt that the absorption into 

 the capillary blood-vessels is an instance of endosmosis with- 

 out intervention of any vital force. All sorts of salts and 

 other diffusible substances, whether simply useless or posi- 

 tively injurious, find their way into them; while it is proved 

 by experiment that such substances do not pass into the lac- 

 teals, at least so rapidly. And this is not altogether inexplic- 

 able; for we have seen that the capillaries are near the surface 

 of the villus, while the lacteal is in the centre, and receives 

 its supplies through the action of nucleated corpuscles. In 

 fact, a little reflection will show that the action of the 

 epithelium in lacteal absorption differs from that of secreting 

 cells in separating substances from the blood in nothing, 

 save that in secretion the current is from vessels to a free sur- 

 face, while in lacteal absorption the current is from a free 

 surface to the interior of a vessel. 



119. The difference in the absorbing power of the lacteals 

 and the blood-vessels has probably a considerable importance, 

 dependent on the different courses taken by the two sets of 

 vessels. The lacteals, which are deeply placed in the villi, 

 and fed by other means than mere endosmosis, send their 

 contents, by the thoracic duct, into the circulation at a point 

 where the blood is returning to the heart and has only to 

 be subjected to the influence of respiration before being 

 diffused throughout the body. The blood-vessels, on the 

 other hand, take up everything according to its diffusibility; 

 but they carry their stream into the portal vein, whence it 

 is conveyed through the capillaries of the liver; and not 

 until it has been subjected to the influence of that organ 

 which has, besides other functions, an arrestive power is it 

 allowed to reach the heart. 



As in the case of intestinal absorption, so also throughout 

 the body, fluids appear to pass into the blood-vessels easily 

 by endosmosis; and the circumstances are not well known 

 which call for the necessity of lymphatics as well as blood- 



