PRACTICAL HISTOLOGY. 



EPITHELIUM. 



EPITHELIUM consists of corpuscles or cells with or without envelopes, of various shapes, 

 sizes, and consistence, united by an intercellular substance or cement. The corpuscles are 

 always disposed on surfaces, and usually contain a nucleus and sometimes a nucleolus ; they 

 may be colourless, though they sometimes contain pigment. They may be arranged in a single 

 layer or in several layers. Each cell regulates its own nutrition and never contains a blood- 

 vessel. The following is a convenient classification of the varieties of epithelium met with 

 in the human body : (i) Squamous, (2) Columnar, (3) Ciliated, (4) Transitional, (5) Secretory. 



i. SQUAMOUS EPITHELIUM. 



PREPARATION. With the finger-nail or a blunt knife scrape off a little of the epithelium 

 lining the inside of the cheek or covering the tongue. Diffuse the scraping in water on a 

 slide, cover and examine. 



EXAMINATION (H). In this preparation only the superficial squames are seen. They 

 are irregular polygonal cells when seen on the flat, and are several times the breadth of a 

 coloured blood-corpuscle. Each cell contains a relatively small nucleus, and not unfrequently 

 fine granules. Occasionally several cells are found adhering to each other by their margins, 

 and sometimes micrococci are seen attached to them. If the edge of a cell be directed 

 towards the observer, it will appear more or less spindle-shaped according to the angle which it 

 forms with the plane of the slide. (Indicate these characters in PI. II., Fig. I.) In addition, 

 small round and finely granular cells, about the size of a colourless blood-corpuscle and con- 

 taining one or two nuclei, may be found here and there in the field. These are the salivary 

 corpuscles. The included granules exhibit Brownian movement a phenomenon which occurs 

 when fine particles are suspended in a watery fluid, and which is probably due to differences 

 of temperature in the several strata of the liquid. Brownian movement is easily shown by 

 rubbing down a little gamboge in water. 



EFFECT OF REAGENTS. Irrigate with a drop of magenta solution (p. xliv). The 

 nucleus stains of a deep red colour, while the peri-nuclear part is but slightly affected. The 

 alcohol in this solution precipitates the mucin of the saliva in the form of fine red threads or 

 red membranous flakes (PI. II., Fig. i). 



Squamous epithelium in exposed situations, as in the superficial layers of the skin, becomes 

 hardened, and forms what is known as the horny layer of the epidermis. 



PREPARATION. With a knife shave off a few of the surface scales of the skin, diffuse the 

 scraping in water, cover and examine. 



