26 EVENINGS AT THE MICROSCOPE. 



charges mucus, and is hence termed mucus membrane. 

 Now this is composed of loose cells, which very easily 

 separate, called epithelial cells ; they are in fact constantly 

 in process of being detached (in which state they con- 

 stitute 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 un discernible by the unaided eye, differ in appear- 

 ance 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 deter- 

 mined it to be blood ? And, particularly, how was it 

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

 averred ? 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. 



