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pitate; in a well stained ganglion or nerve a cold, concentrated, 

 aqueous solution of corrosive sublimate converts the methylenblue 

 into a finely grained purplish precipitate. 



In order to bring such a preparation into paraffine , it must first 

 by dehydrated. The dehydration cannot be accomplished by the use 

 of alcohol, for this fluid dissolves the precipitated color. As a sub- 

 stitute 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 contain ing some corrosive 

 sublimate it remains unaffected. The tissue was therefore dehydrated 

 in a solution composed of I gramme of corrosive sublimate and 5 ccm 

 of methylal. 



The preparation, after being dehydrated, is of course permeated 

 with a strong solution of corrosive sublimate in methylal. To free it 

 from corrosive sublimate and to replace its methylal gradually 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 xylol. After remaining 

 in this mixture a short time the preparation is next placed in a con- 

 siderable quantity of xylol. Here it should remain till all the me- 

 thylal is replaced by xylol and the corrosive sublimate is completely 

 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 imbedded in paraffine and cut in 

 the usual manner. The sections should be fixed to the slide with 

 Schällibaum's collodion and not with Mayer's Albumen which 

 discharges the color. Whole preparations or sections made in this way 

 are serviceable for study for several weeks , but after an interval of a 

 month the finer details in them are likely to fade. 



The principal difficulties met with in employing this method are 

 three : a semicrystalline condition of the precipitate due apparently 

 to overaction of the corrosive sublimate ; incomplete dehydration and 

 imperfect removal of the corrosive sublimate. Remedies for these 

 troubles easily suggest themselves. 



The essential steps in the method can be recapitulated as follows, 

 the lengths of time given being those required for a satisfactory pre- 

 .paration of a ganglion in the ventral nerve chain of the crayfish. 



1) Cold, saturated, aqueous solution of corrosive sublimate for 

 Ì minutes. 



