DIGESTION. 91 



and is separated from the underlying tissues by a thin basal mem- 

 brane. Each cell consists of a granular protoplasm containing an 

 oval, well-defined nucleus lying in its lower half, in which a distinct 

 nucleolus appears. The epithelial cells are joined together in 

 bridges of a protoplasmic nature, with spaces between the bridges 

 filled with cement substance. In cholera and in poisoning by arsenic 

 these cells are shed. Between the epithelial cells roundish structures, 

 either single or in small groups, and of a diameter greater than the 

 epithelial cells, appear. They are quite transparent, have no true 



Fig. 21. Blood-vessels of an Intestinal Villus. (LANDOIS.) 



Cn, Capillaries. A, Artery. Cl, Cylindrical epithelium. O, Surface of the 

 epithelium. V, Vein. 



cell-membrane, and only a thickened ectoplasm, which undergoes no 

 mucoid change. These cells are goblet-shaped, full of protoplasm, 

 containing a compressed nucleus. It is generally considered that 

 these two kinds of cells, the cylindrical and the goblet, are separate 

 in origin ; that is, a young epithelial cell cannot become changed into 

 a goblet cell. The goblet cells discharge mucin, which goes to form 

 the mucus. Fasting, active digestion, and excessive doses of pilo- 

 carpin increase their number. 



Going inward from these cells we meet in the villus a base- 

 ment membrane, immediately beneath it the blood-vessels, then the 



