STEATIFIED EPITHELIUM. 57 



cover- glass with a bristle their true form will be 

 apparent as they tarn over. 



In addition to such cells as these a certain number 

 of much smaller rounded cells may generally be seen 

 in the saliva, which somewhat resemble the white 

 corpuscles of the blood, and, like them, frequently 

 exhibit amoeboid movements. They are, in fact, to 

 be regarded as white blood-corpuscles which have 

 either migrated from the bloodvessels into the sali- 

 vary ducts and have been carried into the mouth 

 with the saliva, or have corne from the mucous 

 membrane covering the back of the tongue and the 

 tonsils, which is very rich in lymph-corpuscles. The 

 saliva being a watery fluid they are swollen out by 

 it, and with a good microscope it may be observed 

 that the granules in the interior of the corpuscles 

 exhibit the Brownian molecular movement, a phe- 

 nomenon which, it will be remembered, was exhi- 

 bited by the white corpuscles of the blood, as a first 

 result of the imbibition of water. 



Preparation 2. Deeper Layers. There are 

 several layers of the above-described large flattened 

 epithelial cells in the epithelium of the mouth. 

 Below them are other cells smaller and of a more 

 spheroidal or polyhedral shape, and many of them 

 having ridges and spines with intervening furrows 

 upon "their surface. To obtain these isolated it is 

 necessary to macerate a piece of any membrane 

 which is covered by a similar scaly stratified epithe- 

 lium in some fluid which, while it softens and dis- 

 solves the intermediate substance which cements 

 the cells together, may preserve their natural form, 

 and, at the same time, prevent putrefaction from 

 appearing in the tissue which is undergoing macer- 

 ation. The best liquid for this purpose is a weak 

 solution of bichromate of potash, 1 part to 800 of 

 water ( per cent,). The portion of tissue must be 

 small, and the quantity of liquid used comparatively 

 large. A piece of the mucous membrane of the 

 mouth, pharynx, or gullet of any mammal may be 



