132 American Quarterly Microscopical Journal. 



as to be able to study their histological elements, and in order 

 to make a thin section they must be hardened ; that is, the 

 water must be extracted from them. The best agent, accord- 

 ing to my experience, is alcohol, properly used. Its advant- 

 ages over other hardening agents, such as Miiller's fluid, 

 chromic acid, osmic acid, etc., are, that the tissues become 

 hard more quickly, the histological elements suffer less distor- 

 tion, and the sections take the staining more readily and 

 brilliantly. 



In hardening tissues in alcohol, they should be cut into pieces 

 not larger than a cubic-inch, and immersed in a sufficient 

 quantity of proof spirits (45^) to fully cover them. After three 

 or four days the proof spirits should be replaced by alcohol of 

 80^ in which the pieces of tissue should also remain 

 three days. After the expiration of this time, they should 

 be placed in 95^ alcohol, which will harden most tissues suffi- 

 ciently in three or four days. Some tissues, however, such as 

 lung, and some pathological new growths, require still further 

 dehydration in Squibb's absolute alcohol, which is in reality 

 99^^. If this plan is pursued, the water is so gradually ex- 

 tracted from the tissue and replaced by the alcohol, that hardly 

 any shrinking takes place, as may easily be verified by compar- 

 ing a section made from a tissue hardened in this way with a 

 section from one that has been frozen while fresh. Of course, the 

 tissue should be as fresh as when put into the first alcohol, for 

 if any post-mortem change has taken place, it cannot be hard- 

 ened by any reagent. Nerve tissue, such as brain and spinal 

 cord, is better hardened for a few days in Miiller's fluid, and 

 then finished with 95^^?^, or absolute alcohol, if necessary. 

 Treated in this way, nerve tissue becomes sufficiently hard for 

 cutting without becoming brittle, as is the case when either 

 Miiller's fluid or alcohol alone is used. If the tissue contains 

 bone and it is desirable to carry the section through it, the 

 earthy salts must be removed, which is best done by immersing 

 the piece in a solution composed of : 



Chromic acid, gr. xv. 



Nitric acid (C. P.), fl. 3 i. 



Water - - - fi. 5 '^'ii- 

 After several days a few drops of nitric acid should be added, 

 and the bone tested for softness by piercing it with a fine needle. 

 After the bone has been sufficiently softened, which will be 



