28 EVENINGS AT THE MIOEOSCOPE. 



must explain that the whole of the internal surface of 

 the body is lined with a delicate membrane (a continu- 

 ation of the external skin), which discharges 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 constantly in 

 process of being detached (in which state they consti- 

 tute the mucus), and of being replaced from the tissues 

 beneath. Now microscopial anatomists have learned 

 that these epithelial scales or cells, which are so minute 

 as to be undiscemible by the unaided eye, differ in ap- 

 pearance 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 pavement ; those that cover the root of the tongue 

 are arranged in cylinders or tall cones, and are known 

 as cohimnar ; while those that line some of the viscera 

 of the abdomen carry little waving hairs {cilia) at their 

 tips, and are known as ciliated epithelium. 



The result of the investigation left no doubt remain- 

 ing 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 not to be the blood of an ox, as the pris- 

 oner 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 



