42 NORMAL HISTOLOGY. 



men and allowed to remain for from two to three 

 minutes. The staining fluid is then washed off by im- 

 mersing the slide in water, or by allowing a gentle stream 

 of water to flow over it. The slide is then allowed to 

 remain exposed to the air until the film of tissue is 

 perfectly dry ; then a drop of Canada balsam is placed 

 on the specimen and a cover-glass put on. The cells in 

 this tissue are, for the most part, extremely thin, and of 

 various, often quite irregular forms, sometimes sending 

 off narrow branching processes, by which they join 

 neighboring cells, and sometimes furnished with wing- 

 like projections. In addition to these cells, and the 

 intercellular fibres, nerves and capillary blood-vessels 

 are sometimes seen in the specimens, and, occasionally, 

 in the vicinity of the vessels are found the above- 

 mentioned plasma cells. 



Pigmented Connective- Tissue Cells of the Choroid. These 

 may be taken from the eye of any mammal (except 

 albinos) which has been hardened in Miiller's fluid and 

 alcohol. A shred of the outer layers of the choroid 

 should be torn off, stained with haematoxylin, and 

 mounted in glycerin. Irregular-shaped, often branched 

 and flattened cells are seen lying embedded in a mem- 

 branous nucleated basement substance, containing deli- 

 cate elastic fibrils, the cells being more or less crowded, 

 except in the part occupied by the nucleus, with a multi- 

 tude of minute brown or black granules. 



Transverse Sections of the Cornea Cells Seen from the 

 Edge. We shall employ for our study here the cornea 

 of the frog, because of the ease with which it can be 

 obtained, and because, on account of its thinness, it is 



