12 On Preparing Tissues for Examination. 



Let the material remain in this for from 24 36 hours, 

 never longer than three days, and then replace it by 

 pure methylated spirit, it may remain in this for an in- 

 definite time, but it will often be found that the spirit 

 becomes cloudy and full of deposits in a few days ; in 

 this case it is only necessary to change the spirit until 

 it remains clear. 



A large quantity of i per cent, solution of chromic 

 acid should be kept on hand, and it should be mixed 

 with the spirit as required, it will be found the most 

 useful of all the hardening agents, if it is changed at 

 the proper times, and it should not be used stronger 

 than is given above, it will even be found beneficial to 

 use it weaker in some cases. 



2. Muller's Fluid is a good hardening mixture, but 

 requires a much longer time, taking weeks to do what 

 the chromic acid mixture will do in days. It is made 

 thus : 



Take 



Potass. Bichrom. 2 parts. 



Sodse Sulph. 1 part. 

 Water 100 parts. 



The advantage of this mixture is that larger pieces 

 can be hardened in it, and it does not require 

 changing after the first week or two, but it will take 

 from 5 7 weeks to harden anything according to 

 its size. The material, when sufficiently hardened, 

 should be well washed and then placed in dilute spirit 

 in the same manner as recommended after hardening 

 in the chromic acid mixture. 



