190 THE MICROSCOPIST. 



digestion a mixture of albuminous and fatty matters, 

 which is known as chyle, and these vessels have obtained 

 the name of lacteals. The cells in this fluid are leucocytes, 

 identical with white cells in blood. They originate in the 

 lymphatic glands and " Peyer's patches " of the intestine, 

 and are the corpuscles of these organs which have been 

 carried off by the fluid stream. 



III. Mucus. 



Is a tenacious semifluid substance which covers the 

 surface of mucous membranes. It contains cast-off epi- 

 thelial and gland-cells, and the mucus corpuscle, which, as 

 we have before said, is identical with other leucocytes. 

 Synovial fluid is of similar nature. It is now regarded as 

 a transformation product of the epithelial cells, and not 

 to originate as a secretion from special glands (Plate 

 XVIII, Fig. 141). 



2. EPITHELIUM AND ITS APPENDAGES. 



Epithelium (from e/n, upon, and OaMta, to sprout) is so 

 called since it was formerly supposed to sprout from mem- 

 brane. It is a tissue formed of cells more or less closely 

 associated, which is found in layers upon external and 

 internal surfaces. The cells are generally transparent, 

 with vesicular, homogeneous, or granular nuclei, the lat- 

 ter being the remains of the original leucocyte or bio- 

 plast. In the older cells the nucleus is absent, the entire 

 mass having been transformed. 



The forms of epithelial cells vary according to situation 

 or function. The original form is spheroidal, but changes 

 by compression, etc. 



1. Tessellated or pavement epithelium (Plate XVIII, 

 a, Fig. 142). These are cells whose formed material is 

 flattened, and which are united at their edges. They are 

 sometimes hexagonal, and often polyhedral, in form. 



Examples : Serous and synovial membranes ; the pos- 



