Method VII 45 



nerve terminations, as the case may be, show a satisfactory blue 

 color not possessed by the other tissues. Care must be taken 

 to catch the stage at which the stain has reached its full 

 development, for the color is very apt to soon fade or become 

 diffuse, and thus result in inferior preparations. 



3. To fix.— As soon as the stain has satisfactorily developed, 

 plunge the pieces of tissue immediately into a vessel containing 

 20-30 volumes of the saturated aqueous solution of ammonium 

 picrate (C, i), and let remain for 6-24 hours. In this solution 

 the blue color is changed to a brownish purple hue. 



4. To preserve and mount. — Transfer from the aqueous picrate 

 solution to 4 or 5 volumes of the ammonium picrate-glycerine 

 mixture (D) for another 6-24 hours. The tissues, however, 

 may remain in this mixture for days, or even weeks, without 

 injury. 



To mount, transfer small pieces to the slide, tease as much 

 as examination under the microscope shows to be necessary, and 

 mount in a fresh drop of this same ammonium picrate-glycerine 

 mixture. 



If the preparation is good, and it is desired to keep it for 

 study or demonstration, it is safer to seal down the cover- 

 glass with zinc cement or gold size. It is sometimes suggested 

 to mount in glycerine jelly (IV, E, p. 32) which has been satu- 

 rated with ammonium picrate, but such preparations often prove 

 less permanent than those mounted in the above mixture. 



The jelly is warmed till well melted and the ammonium 

 picrate crystals added in such an amount that, after an hour, 

 undissolved crystals remain in the mixture, which has been kept 

 warm and shaken from time to time. 



Preparations are fixed and mounted in the ammonium picrate- 

 glycerine mixture as above, when it is desired only to study the 

 relations of the elements to each other in their coarser detail. 

 The general course of the axones, the general arrangement of 

 their terminal branches in end-organs, their arrangement in 

 nerve plexuses, or the relation of the efferent and afferent axones 

 to the cell bodies in ganglia may, indeed, be better studied in 



Digitized by Microsoft® 



