2o2 THE MICROSCOPE AND 



Thoroughly wash in water, not in alcohol, which precipitates the 

 ferro-cyanide solution. Then dehydrate with absolute alcohol, 

 clear by means of xylol or origanum oil. These re-agents do not 

 affect the celloidin. Mount in Canada balsam or dammar. 



A slight modification is as follows : — Harden the material in 

 bichromate of potash, follow by alcohol, embed in celloidin, cut 

 sections, and immerse them in a half-saturated acetate of copper 

 solution for twenty-four hours, and then in alcohol for a few 

 minutes. After this put the sections into a solution of hsematoxy- 

 lin for twenty-four hours, and wash in water for a few minutes. 

 Then transfer them to a solution of ferro-cyanide of potash till 

 the colour is washed out, except from the medullated fibres. I 

 find this very good for cord of Tabe's dorsalis and brain sections. 

 Some regard the acetate of copper as a hardening agent, which it 

 is not, and if used as such the tissue will be spoilt. 



The only drawback to Weigert's method is that sections must 

 be cut and stained immediately after hardening and before trans- 

 ferring to alcohol. If pieces after hardening have been in alcohol 

 so long as to become green (a change which takes place in all 

 chromic acid specimens after being kept in alcohol), the staining 

 will fail. To obviate this, the tissue is subjected to the celloidin 

 process, and fixed on a piece of cork in the usual way. Then 

 place in a beaker, with the saturated acetate of copper solution (as 

 above), diluted with an equal quantity of water, and the whole 

 placed in a hot-air bath, and kept at between 35'' to 45*^ C. for 

 two days ; after which cut sections and stain as before. By this 

 method, heating hsematoxylin is unnecessary while staining, and 

 the differentiating fluid should be diluted with an equal volume of 

 water. 



Chloral Hydrate Method.— Harden in Miiller, bichromate of 

 potash, or if a faster reaction is required, ammonium bichromate 

 may be used, or a 10 per cent, solution of chloral hydrate. 

 Change after twenty-four hours and again at the end of the third 

 day, and at the end of the first, second, and fourth weeks ; after 

 which the cord may be left in the fluid until it is transferred to the 

 gum and syrup solution before the sections are made. Stain and 

 mount as required. 



