'26 EVENINGS AT THE MICROSCOPE. 



•charges mucus, and is hence termed mucous membrane. 

 Now this is composed of loose cells, which very easily 

 separate, called epithelial cells ; they are in fact con- 

 stantly in process of being detached (in which state they 

 constitute the mucus), and of being replaced from the 

 tissues beneath. Now microscopical anatomists have 

 learned that these epithelial scales or cells, which are so 

 minute as to be undiscernible by the unaided eye, differ in 

 appearance and arrangement in different parts of the body. 

 Thus, those which line the gullet and the lower part of 

 the throat are tesselated, or resemble the stones of a pave- 

 ment ; those that cover the root of the tongue are 

 arranged in cylinders or tall cones, and are known as 

 columnar; while those that line some of the entrails 

 carry little waving hairs {cilia) at their tips, and are 

 known as ciliated epithelium. 



The result of the investigation left no doubt remaining: 

 that with that knife the throat of a living human being, 

 which throat had been protected by some cotton fabric, 

 had been cut. The accumulation of evidence was fatal 

 to the prisoner, who without the microscopic testimony 

 might have escaped. 



But what was there in the dried brown stain that 

 determined it to be blood % And, particularly, how was 

 it proved to be not the blood of an ox, as the prisoner 

 averred 1 To these points we will now give a moment's 

 attention. 



With this fine needle I make a minute prick through 

 the skin of my hand. A drop of blood oozes out, with 

 which I smear this slip of glass. The slip is now on the 

 stage of the instrument, under a power of 600 diameters. 

 You see an infinite number of small roundish bodies, of 

 a clear yellowish colour, floating in a colourless fluid, but 

 so numerous, that it is only here and there, as near the 

 edges of the smear, that you can detect any interval in 

 their continuity. 



