58 PRACTICAL HISTOLOGY. 



used ; it will require at least two or three weeks' 

 maceration (for in this kind of epithelium the cells 

 are very closely united), and the bichromate solution 

 should be changed every third day. At the expira- 

 tion of the time stated a small portion of the epi- 

 thelium is scraped oft' with the point of a knife and 

 placed in a drop of water upon a slide. It is then 

 broken up as finely as possible with a pair of mount- 

 ed needles, a piece of a hair is cut off and placed in 

 the drop, and the cover-glass is superposed. By far 

 the majority of the cells seen are the superficial ones 

 already described ; but others may be found which 

 are less flattened and smaller in diameter, and have 

 many of them an irregular toothed margin, their 

 surface also, as may be seen by altering the fine 

 adjustment of the microscope, having on it linear 

 or punctated markings. These are the cells with 

 ridges and spines above . mentioned ; they will be 

 again studied in sections of the skin, as well as in 

 sections of these and other mucous membranes which 

 are covered with similar epithelium. 



Preparation 3. Horny Layer of Epidermis. 

 If a very small shred of the superficial part of the 

 epidermis is taken from any part, the palm of the 

 hand, for instance, and examined in water under 

 the microscope, no indications of cellular structure 

 are visible nothing but a hard horny confused mass 

 is to be seen. Remove the cover-glass and place the 

 shred of epidermis in a drop of liquor potassse. It 

 will soon swell up and become soft. When this is 

 the case return it to the water, and, after breaking 

 it up as finely as possible with needles, cover and 

 examine. Numerous spheroidal cells are now seen 

 loose in the preparation, with a distinct contour, as 

 if inclosed by a membrane, but without a nucleus. 

 They are, in fact, the scaly cells, which have become 

 swollen out by imbibition of water, and at the same 

 time, in consequence of this swelling of their sur- 

 faces, correspondingly diminished in width. 



The same result may be obtained with the cells 



