CHAPTEE II. 



ON PEEPABING TISSUES FOE EXAMINATION. 



THE most essential point in microscopic investigation is 

 the proper hardening of the material to be examined, 

 and this must be done gradually, as if any tissue is 

 placed in a strong solution, the elements of which 

 it is composed at once shrink, and it is impossible to 

 form any correct idea of their nature. 



1. Chromic Acid Mixture. The most useful harden- 

 ing agent is a mixture of chromic acid and spirit. Make 

 a solution of chromic acid in water 15 grains to the 

 pint, this is about ^ per cent. Take of this 2 parts ; 

 methylated spirit 1 part. 



The material must be cut into small pieces about half 

 an inch square, and a large quantity of fluid used, a wide 

 mouthed stoppered bottle holding from 6 10 ozs., ac- 

 cording to the quantity of material, is best ; change the 

 fluid at the end of 24 hours, and again every third day, 

 and the material will be hardened in from 8 12 days, 

 this can be easily proved by taking out a piece and feel- 

 ing it. If allowed to remain too long it gets brittle. 

 When it is found to be moderately hard, usually after 

 about 9 10 days, pour off the chromic acid mixture, 

 and wash well, replace it by dilute spirit made thus : 



Take 



Methylated Spirit 2 parts, and 



Water 1 part. 



