6 METHODS. 



solution hardening goes on very slowly, or not at all. The 

 hardening may be accomplished by the solution of chromic acid 

 as described above, or by alcohol. The latter method is the best 

 for preservation of brain specimens, which, by the slightest 

 excess of chromic acid, become too brittle to be cut. Eyes are 

 placed fresh into Muller's liquid (two parts of bichromate of 

 potassa, one part of sulphate of soda, and 100 parts of water). 

 After a few weeks the eye may be cut open and transferred into 

 a one-half per cent, solution of chromic acid, or into strong alcohol, 

 in order to accomplish the hardening process. The advantage of 

 these re-agents is that they do not interfere with the structure 

 of the tissue, and render all constituent parts very distinct. 

 Chromate of ammonia or picric acid solutions are by no means 

 superior to the above- described liquids. Alcohol, for preser- 

 vation of specimens, is objectionable, as it makes the tissues 

 shrink, and leaves them too pale and indistinct for good observa- 

 tion. Specimens kept in alcohol for a while should be placed in 

 a one-half per cent, solution of chromic acid, in which they harden 

 very quickly, and become well adapted for microscopic purposes. 

 Bone and teeth, after a long-continued action of chromic acid, 

 on account of the reduction of the latter, assume a dark green 

 color, without change of their structure. 



Cutting. After the specimens have become sufficiently hard, 

 they are ready to be sliced into thin and transparent sections. 

 For this purpose a good razor, flattened on the side which slides 

 on the specimen, is the simplest and most convenient tool. The 

 specimen is rid from chromic acid by being placed in water it 

 is held in the left hand, flattened out by one stroke of the razor, 

 and the flat surface is kept in a horizontal position over a china 

 soup-plate filled with water. We take up a little water on the hol- 

 low surface of the razor, and, while the water runs over the level 

 of the specimen, the razor is drawn slowly and uniformly through 

 the tissue without producing ridges. The thinner the specimen 

 the better. With the assistance of a flat copper spoon and a 

 needle, the thin sections are transferred to a china saucer hold- 

 ing water, in which, if desired, staining re-agents are applied. 

 Common water answers all purposes, and neither alcohol nor 

 distilled water are required. Small or hollow specimens, which 

 cannot be held in the left hand, such as halved eyes, teeth, etc., 

 must be imbedded in the following way: The hardened specimen 

 is placed in strong alcohol for twelve to twenty-four hours, in 

 order to be rid of its water. A square paper box, according to 



