376 SOME HARDENING AGENTS. 



keeping well covered and air-tight. Hardening in Miiller can be 

 hastened by raising the temperature to 30 or 4o^C. (8o-ioo°F). It 

 should be changed the first, second, and fourth days, and as often 

 afterwards as it is discoloured, and then left alone except for an 

 occasional stir. A large quantity of fluid should always be used. 

 The spinal cord of a dog or cat requires about a litre of the agent. 

 Harden in a dark, cool place. If a quicker solution is required, 

 use Miiller's fluid and spirit, three parts to one. 



If a Brain is being hardened, inject it daily with the fluid, keep 

 it for four or five days in a jar of the same fluid, change daily, and 

 then it can be cut up as desired. To hasten the hardening of a 

 brain or spinal cord that has been in Miiller's fluid for three or 

 four weeks, a two per cent, solution of bichromate of ammonia 

 will do it very nicely in about fourteen days if the fluid is changed 

 daily. These agents are particularly good for nerve-tissues, brain, 

 spinal cord, retina, intestinal muscle, and glands. 



Erlicki's Fluid is another good agent, and is very similar to 

 Miiller, but contains half per cent, of sulphate of copper, instead 

 of one per cent, of sulphate of soda ; it is quicker in its action, 

 and this can be hastened if the tissues are kept for a day or two in 

 it at a temperature of 4o°C. Two days or so are sufficient under 

 these conditions. 



Chromic Acid. —This is best when used as a one-sixth per cent, 

 chromic acid. Take of it two parts, and spirit one part, and stir. 

 Cut the tissue in pieces not larger than one-fourth of an in. square, 

 and put them in a quantity of the fluid. First day, put the tissue 

 in the fluid. On the second, fifth, and eighth days, change the 

 fluid. On the ninth day, put the tissue in a weak spirit mixture 

 (two parts alcohol and one water ; stir). Tenth day, remove to 

 pure spirit. On the fourteenth day, [mt it in plain water. On the 

 fifteenth, remove to a fairly thick solution of mucilage. On the 

 sixteenth day, put sections into hot distilled water to soak out the 

 gum, then change to alcohol. Stain and mount. The weak spirit 

 mixture is made of two parts spirit and one part water. On the 

 fourteenth day the hardening process is complete, and the speci- 

 men may be left in the pure spirit for any length of time, but if it 

 is desired to cut sections the rest of the directions should be 

 followed. 



