ELEMENTARY HISTOLOGY. 35 
Chap, III—ELEMENTARY HISTOLOGY. 
When examined under the microscope all the different tissues 
and organs of the body are found to consist of elementary bodies 
called cells, and of an intercellular substance connecting the 
several cells together. These cells, of which a white blood 
corpuscle is a typical example, vary much in shape, size, and 
structure in different tissues, but are to be considered as 
fundamentally equivalent to one another. The intercellular 
Substance varies very much in quantity; it may be almost 
absent, so that the several cells are practically in contact with 
one another ; or may be so abundant as to separate them widely : 
it is to be viewed as formed by the cells, and therefore as 
secondary in importance to them. 
A. Epithelium. 
Epithelium consists of cells placed side by side so as to form 
layers, which cover the surface of the body (epidermis) and line 
the alimentary canal and the various internal cavities of the 
body. At the external apertures of the body the epidermis 
becomes directly continuous with the epithelial lining of the 
internal cavities. 
The layers may be one or more cells in thickness: in the 
former case the epithelium is said to be simple, in the latter 
stratified. 
Epithelium is of different kinds, according to the shape and 
structure of its component cells. 
I. Squamous Epithelium: the component cells are flattened 
parallel to the surface they cover : if the epithelium is stratified 
the flattening is most marked in the most superficial cells. 
a. Isolated cells. 
Scrape gently the imside of your cheek with the handle of a 
scalpel, and put the scrapings on a slide ; cover and examine with 
a high power: draw, showing :— 
i. Shape: large flattened scale-like cells, often slightly 
curled up at the edges. 
ii, The nucleus: oval and granular: near the middle 
of the cell: rendered more distinct by acetic acid 
or magenta. 
