[ 179 ] 



Zbc flDicro0Copc anb Ibow) to '\ri6C it 



By V. A. Latham, F.M.S. 

 Part VII. 



Hardening Agents. — The most essential point in microscopic 

 investigation is the proper hardening of the material to be exa- 

 mined, 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 a correct idea of their nature. 

 It will be impossible to give more than the usual strengths of the 

 fluids, as it is only by constant practice and experience that the 

 strengths can be learnt ; each fluid differing slightly for the various 

 organs, and most histologists use various strengths. Hardening 

 solutions, as a rule, do not require filtering. The best plan is to 

 make a large quantity at a time — say, a Winchester quart,* which 

 holds about 2,400 cc. of water. This quantity should be mea- 

 sured into the bottle, and the height of the fluid marked on it with 

 a diamond. The amount of the chemical used should be written 

 on the label, so that when a new supply is wanted the bottle has 

 only to be held under the tap until the water reaches within a few 

 inches of the mark. The quantity of the hardening agent is then 

 weighed out and put in the funnel, and the bottle filled up to the 

 mark. This method answers with substances which dissolve 

 readily ; others have to be pounded in a mortar with warm water. 



A. — Hardening. 



Chromic Acid, i per cent, solution. — Weigh 10 grammes of 

 crystallised chromic acid, and dissolve in i litre of distilled water. 

 This can be diluted as required. I generally make a i — 6th per 

 cent. (15 grammes to the pint). 



Chromic Acid and Spirit.— The most useful hardening agent 

 is this mixture : — Make a i — 6th per cent, solution — i gramme to 

 600 cc, or 15 grains to the pint. Take of this 2 parts, and ordin- 

 ary methylated spirit i part. Stir and allow to cool before using. 

 To use the solution, the material must be cut into small pieces, 



* A Winchester quart is a'glass bottle holding about half-a-gallon, — Ed. 



