82 CARMINE STAINS. 



great merit of being as innocuous as possible to most tissues. 

 It is a single or a double-stain according to the manner of 

 using it. If the preparations be washed, after staining, with 

 water, it is a single stain, the colour of the carmine alone 

 appearing ; if they be washed quickly in alcohol it is a double- 

 stain, the yellow colouration of the picric acid not being dis- 

 solved by the alcohol as it is by water. Of course the washing 

 with alcohol must not be overdone, or the yellow colouration 

 may be entirely removed. 



For slow staining, dilute solutions may advantageously have 

 1 or 2 per cent, of chloral hydrate added to them. 



Over-stains may be washed out with hydrochloric acid, say 

 0*5 per cent., in water, alcohol, or glycerin. 



Preparations should be mounted in balsam, or if in glycerin 

 this should be acidulated with 1 per cent, of acetic or, better, 

 formic acid. 



The good qualities (especially that of precision and delicacy 

 of stain), above attributed to picro-carmine, apply in their en- 

 tirety only to Ranvier's picro-carmine or picro-carminate of 

 ammonia. The other pseudo-picro-carmines are in general so 

 inferior as not to take rank as good stains at all. The reader 

 is in consequence warned against an over-confident faith in 

 them, and is especially warned against the so-called picro- 

 carmine sold by the opticians. The true Ranvier's picro-carmi- 

 nate of ammonia can only be prepared with certainty by one 

 process as yet known. This I proceed to give, and amongst 

 the other formulae set out one or two that may by chance give 

 rise to the formation of a picro-carminate, and should at all 

 events afford a useful staining solution (which the majority of 

 these formulae only do by chance) . 



145. Ranvier's Picro-Carmine or Picro-carminate of Ammonia. 

 The method of preparation employed in the Laboratory of 

 Histology of the College de France, kindly communicated to 

 myself and Henneguy for our Traite des Meth. Techn. (q. v., 

 p. 451) by M. VIGNAL, one of the assistants there, is as follows : 

 Take 



Water 1000 parts. 



Picric acid . . . . 20 

 Carmine . . . . 10 

 Ammonia . . . . 50 



