1560 Journal of Applied Microscopy 



The oil of cajeput will clear the sections within a few seconds in perfectly 

 dry air ; but under the usual conditions of the laboratory, it is desirable to 

 hasten the action by warming the slide gently. Mount in a thick solution of 

 colophonium dissolved in xylol. 



A word concerning colophonium may not be out of place here. Colophonium 

 is the ordinary •' rosin '' of commerce. It is best to secure the privilege from 

 the dealer of selecting those lumps which have the least possible color. When 

 held up to the light, a suitable lump should not show crystals on the inside. 

 The powdered rosin of dealers should be avoided, since its character cannot be 

 determined. 



When the several steps of the method as outlined are followed faithfully, the 

 staining wnll be so precise that the nerve-cells will appear bright blue on a per- 

 fectly colorless field. Moreover, the tigroid bodies should not appear blurred in 

 any part of the ner\-e-cell. As to the permanence of the stain, slides stained by 

 me several years ago have shown no tendency to fade. 



3. Methylcn-Blue and Eryth rosin. 



Staining with methylen-blue alone, as just noted, simply outlines the bodies 

 of nerve-cells. As an accessory demonstration, it is often quite desirable that 

 the remaining structures present be given a light stain. This may be accom- 

 plished through the use of the following double-staining method. 



The tissues should be treated, and the sections should be cut and affixed to the 

 slide as in the piocedure given for the method of Xissl. But, instead of staining 

 with methylen-blue at once, this is preceded by the erjthrosin mixture of Held : 



Erythrosin (^Griibler) . . . . l gram. 



Distilled water ----- 150 c. c. 



Glacial acetic acid ----- 2 drops. 



The acetic acid tends to precipitate the erj'throsin, and so the stain should be 

 made shortly before using. Warm the mixture, pour it over the slide, and allow 

 it to act for some ten seconds, only. Rinse with distilled water for about thirty 

 seconds ; the red color should be made distinctly lighter. 



Now dilute some of the regular stain of Xissl with an equal volume of a five 

 per cent, aqueous solution of acetone. Heat the mixture rather strongly, flood 

 the slide with it, and allow staining to proceed for five minutes. Then difier- 

 entiate the stain with : 



Distilled water ----- 100.0 c. c. 



Common alum ------ .1 gram. 



The solution of alum extracts the blue color gradually, so that the effect is readily 

 controlled. From one to two minutes will usually sufiice to bring the red of the 

 erythrosin distinctly into view. Follow with a brief rinsing in water. Dehydrate 

 rapidly with absolute alcohol, clear in xylol, and mount in xylol-colophonium. 



A successful preparation should have the nerve-cells outlined in bright blue 

 on a pale red field. Too deep a stain with erythrosin must be avoided. 



4. Chro7)U'Silver Impregnation. 



The principle of this remarkable method involves the formation of a deposit 

 of chrome-silver in the elements of the nervous system. This is accomplished 



