EPITHELIUM AND ENDOTHELIUM. 



12' 



in the form of the cells towards the free surface of the epidermis 

 (tig. 86), where they become corneous and less granular. 



(c.) Note in the deeper layers of the epithelium prickle-cells. 

 Adjacent cells are connected by very fine processes or " intercellular 

 bridges." The fine spaces between the bridges 

 are called "intercellular channels." When 

 these are broken across and the cells isolated, the 

 cells present the appearance of being beset by 

 very fine processes, and hence they are called 

 " prickle-cells." 



(//.) The cells vary in their shape and characters 

 from below upwards. It will be easy to detect 

 the horny layer above, composed of many layers 

 of flattened, hardened cells. This forms a fairly 

 well-marked layer, the cells being clearer than 

 those situated more deeply ; the nuclei are less 

 conspicuous, and the cells generally stain yellowish 

 with picro-carmine. 



5. Non-Corneous Stratified Epithelium from F i "" 8 6.-v.s. MUCOUS 

 the (Esophagus (H). Macerate the mucous 



membrane of the oesophagus of a calf or other 

 animal for a week in y 1 ^ per cent, bichromate of 

 potash. This "dissociates" the epithelial cells, 

 so that when the surface is scraped, one obtains 

 isolated cells. Make a cover-glass preparation 

 (p. 114), and stain it in aniline- water-gentian- 

 violet, i.e., gentian-violet solution dropped into 

 aniline water (p. 73). Dry and mount in balsam. 



(a.) Observe the isolated squamous cells, each with a small ex- 

 centrically-placed nucleus stained of a violet tint. Numerous facets 

 are seen in the cells, and their shape both on the flat and on edge 

 can be carefully studied. 



(b.) If desired, stain some in picro-carmine. This is best done by 

 keeping them in the picro-carmine on a slide placed under a bell-jar, 

 with water to prevent evaporation, i.e., in a moist chamber. 



6. Horny Epidermis. Macerate a shred of epidermis in 35 per 

 cent, caustic potash. After a time it is softened and can be broken 

 u I ) with needles. The cells fall asunder and swell up in the fluid, 

 and appear as spheroidal cells with a membrane, but no nucleus is 

 visible. Examine them in the potash solution. No water must be 

 uddcd, else the cells are dissolved. 



7. Prickle Cells (H). Place for twenty-four hours in i per 

 cent, osmic acid a small piece of the palmar surface of the skin 

 less than one-eighth of an inch cube from a freshly-amputated 

 finger. Make vertical sections by freezing, or after embedding in 



Membrane of Hard 

 Palate of Cat. Epi- 

 dermis with cor- 

 neous and deeper 

 layers with prickle 

 cells. Below, con- 

 nective tissue of 

 the mucous mem- 

 brane with a papilla. 

 Chromic acid and 

 spirit, picro - car- 

 mine, Farrant's 

 solution. 



