MICROSCOPICAL TECHNIQUE. 81 



fibres in the peripheral as well as the central nervous organs were 

 stained intensely blue. 



" Preparations made in this way, after being removed from the 

 animal, retain their colour only about an hour, but, as is well 

 known, they can be made more nearly permanent by treating them 

 with reagents, which precipitate the methylen-blue, such as picric 

 acid, ammonium picrate, potassic iodide, potassic ferro-cyanide, 

 chromic acid, or corrosive sublimate. Of these reagents, the one 

 last named, in addition to being an excellent fixing reagent, yielded 

 the most satisfactory precipitate. In a well-stained ganglion or 

 nerve, a cold, concentrated, aqueous solution of corrosive subli- 

 mate converts the methylen-blue into a finely-grained purplish 

 precipitate. 



" In order to bring such a preparation into paraffin, it must 

 first be dehydrated. The dehydration cannot be accomplished by 

 the use of alcohol, for this fluid dissolves the precipitated colour. 

 As a substitute for alcohol, two fluids — aceton and methylal — were 

 tried. In aceton the precipitate is as soluble as in alcohol, and in 

 pure methylal it is also slightly soluble ; but in methylal containing 

 some corrosive sublimate it remains unaffected. The tissue was, 

 therefore, dehydrated in a solution composed of i gramme of cor- 

 rosive sublimate and 5 ccm. of methylal. 



"The preparation, after being dehydrated, is, of course, per- 

 meated with a strong solution of corrosive sublimate in methylal. 

 To free it from corrosive sublimate and replace its methylal gra- 

 dually with xylol is the next step. This is in part accomplished by 

 putting it next into a mixture composed of two parts xylol, one 

 part pure methylal, and one part of the dehydrating mixture of 

 methylal and corrosive sublimate. In this mixture some of the 

 corrosive sublimate is washed out and a part of the methylal is 

 replaced by the xylol. After remaining in this mixture a short 

 time, the preparation is next placed in a considerable quantity of 

 xylol. Here it should remain till all the methylal is replaced by 

 xylol and the corrosive sublimate is washed out. As the last- 

 named substance is only slightly soluble in xylol, the preparation 

 should stay in this fluid some four or five days. At the end of 

 this time it may be either mounted in xylol balsam and studied as 

 a transparent object, or embedded in paraffin and cut in the usual 



International Journal of Microscopy and Natural Science. 

 Third Series. Vol. III. g 



