EPITHELIUM. 43 



of the cell protoplasm, and, by special methods of staining, it is 

 sometimes possible to follow them from one cell through another 

 into a third (Fig. 25). Between the intercellular bridges there 

 are spaces filled with intercellular substance. These spaces can 

 be injected from the lymph-vfessels, and are therefore supposed 



FIG. 25. 



From a section through the stratified pavement epithelium of the human epidermis. X 700. 

 Some cells of the stratum spinosum are bound together by protoplasmic bridges. 



to have the functions of lymph spaces. This would supply the 

 nourishing fluids which the lack of other vessels in the epider- 

 mis makes necessary. 



Epithelium possesses, as a rule, neither blood- nor lymph- 

 vessels. Only in a few places have capillary branches in the 

 epithelium been described definitely (auditory organ "Retzius, 

 mucous membrane of the gums in amphibia Maurer, etc.). 

 Nerves, on the other hand, are abundant. 



The flat epithelium of blood-vessels and lymph- vessels, as 

 well as the epithelium covering the serous membranes, shows in 

 certain places holes, the so-called stomata or stigmata. These 

 are fine openings in the cement substance sufficiently large to 

 admit white blood-corpuscles. According to some authors 

 (Arnold) these structures are not preformed, but are the 

 result of stretching. 



Changes may take place in the protoplasm of the cell due 

 to pathological processes, and give rise to appearances not at 

 all characteristic of the normal cell. The more common of these 

 are, the formation of vacuoles, the fattv degeneration in which 



