METHODS. f 9 



the rim of varnish, and the specimen becomes spoiled. As an 

 inclosing varnish, asphalt dissolved in turpentine is generally 

 used, though any other varnish answers the purpose if put on 

 in sufficient quantity. The mounting and varnishing of glycer- 

 ine specimens is easier with square than with circular covering- 

 glasses. 



Staining. The ammoniacal carmine solution (Gerlach) is the 

 most satisfactory for staining specimens obtained after hardening 

 in chromic acid solution. To the best cochineal powder we add 

 distilled water and a few drops of aqua ammoniae fortis, until 

 the cochineal is completely dissolved. The amount of the car- 

 mine solution to be poured into the saucer holding the sections 

 depends on the concentration of the solution. The best way is 

 to take but little carmine, and let it act on the specimen for 

 twenty-four hours. The various compounds of carmine in use 

 may be dispensed with, as all carmine staining is very unreliable, 

 and, except for the handsome appearance it gives . to the speci- 

 men, of no material value. 



Haematoxylon (logwood) and eosine are re-agents used for 

 alcohol specimens exclusively, but not suitable for chromic acid 

 preparations. The action of the picric acid is kindred to that of 

 chromic acid. Aniline colors as a rule are not fast, neither are- 

 solutions of picro-indigo. 



Osmic acid (M. Schultze) in a one per cent, solution stains fat 

 black in both the fresh and the preserved condition of the speci- 

 men ; it renders the contours of the tissue, especially nervous tissue, 

 more distinct, but otherwise has a very limited value. 



Important re-agents are the nitrate of silver (Von Eeckling- 

 hausen) and the chloride of gold (Cohnheim) ; though specimens 

 treated with either of these re-agents become indistinct after five 

 or six years. Nitrate of silver is brought into contact, in a one 

 per cent, or two per cent, solution (kept in black bottles), exclu- 

 sively with fresh specimens, for only a few minutes, or used for 

 injections into blood and lymph vessels.' Distilled water is needed 

 for washing off the re-agent. The solid nitrate of silver may be 

 applied directly on dense tissues, such as cornea or cartilage, 

 though the layers which come in direct contact with the stick 

 are destroyed. Silver-stained specimens are suitable for glycer- 

 ine mounting. 



Chloride of gold is invariably used in a one-half per cent, 

 solution, and is fit for fresh and frozen specimens, as well as for 

 those preserved in chromic acid ; in the latter case, after careful 



