256 DIGESTIVE SYSTEM. 



tissue, having a large number of embryonic or plasmatic cells. 



In this tissue are found two 

 vascular systems, the first being 

 a network of blood vessels 

 placed throughout the deeper 

 tissues, and especially near the 

 surface, so near that they almost 

 touch the epithelium. The sec- 

 ond is a central tube, the ex- 

 Fig. 68 Us. m tremity of a chyle-duct: it 



columnar epithelium * . J , y 



terminates at the summit or 

 the body of the villus, but in a manner at the present time 

 unknown (see lymphatic system, p. 201, above). Some main- 

 tain that it terminates in a cul-d&-sac, and others that it is 

 gradually blended with the substance of the body of the 

 villus or papilla. However this may be, the general appear- 

 ance would lead to the belief that this tube is only the 

 excretory tube of the network of blood-vessels, in the midst 

 of which it is placed. We see thus that the blood-vessels 

 are better fitted for absorption than the chyliferous vessels. 1 



When the stomach pours its contents into the small intes- 

 tine, the villi, both the epithelium and the body of the villus, 

 change their appearance as the fluid passes through. This 

 phenomenon may be artificially produced by taking the fluid 

 from a stomach in which digestion is going on, filtering it, 

 and bringing it into contact with the intestinal mucous, 

 recently taken from the body and still living. Any other 

 substance than the contents of the stomach, that is, any 

 element which has not been diluted with a large amount of 

 gastric juice, would produce no effect upon the intestinal 



1 According to some recent researches by Debove (" Compt. 

 rend, de 1' Academic des Sciences." Decembre, 1872), these deep 

 cells form an endothelial layer, that is to say, formed of cells iden- 

 tical with those which cover the serous membranes, flat cells 

 joined together by a very fine cement : they are made visible by 

 employing nitrate of silver. What His saw in the villi, and de- 

 scribed as the casing of a central chyliferous vessel, would be, 

 according to Debove, precisely the endothelial or sub-epithelial 

 layer belonging to the surface of the villus. 



* a, Four cells joined together, seen from the side ; the free surface (at 

 the top) shows a thick border, striped with tine striae, b, Similar cells, their 

 disengaged surface being inclined upwards and outwards : the hexagonal form 

 of the section and the thick edge should be remarked, c, Cells modified and 

 slightly distorted by imbibition, their upper edge appearing ravelled. ( Virchow.) 



