2 NORMAL HISTOLOGY. 



structural feature is to be brought into prominence. 

 All of these indications in the histological technique 

 are to be met in such a way as to leave the struc- 

 tures under investigation in as natural a form as 

 possible. Finally, specimens suitably prepared for 

 examination are, in many cases, to be rendered per- 

 manent for future reference and study. 



We will now consider briefly some of the methods 

 by which these indications may be fulfilled. Most 

 histological specimens are laid in some enclosing 

 fluid medium, on a glass plate and covered with a 

 thin slip of glass, before being brought upon the 

 microscope. One of the simplest methods of study- 

 ing tissues is to place them, when quite fresh and 

 after they are reduced to a condition of suitable 

 tenuity, on a slide with some fluid which alters their 

 physical condition but little or not at all, or at least 

 very slowly, and examine them at once. Such a 

 fluid is called an indifferent fluid, and for most pur- 

 poses a dilute solution of common salt, one half to 

 three quarters per cent., answers very well. 



The examination of fresh tissues is very important, 

 not only because it enables us to study the vital 

 phenomena in certain elements, but because we are 

 thus enabled by comparison to determine the 

 amount of change which tissues undergo when pre- 

 pared by more elaborate methods. Still it is in 

 many respects unsatisfactory. In the first place, it 

 is not always easy to procure fresh tissues for every 



