ALCOHOLIC HYDROCHLORIC ACID-CARMINE. 89 



staining in the mass, and there can be little doubt that it is 

 deservedly so. 



Baumgarten makes a " Borax-picro-carmine " by adding 

 crystals of picric acid to Grenadier's solution until it assumes 

 a blood-red colour (Journ. Roy. Mic. Soc., 1888, p. 676; 

 1889, p. 149). 



164. Alcoholic Hydrochloric Acid-Carmine. This reagent is 

 important on account of its allowing a very powerful stain to 

 be obtained by means of very highly alcoholic solutions. That 

 is evidently a very precious quality for work with impermeable 

 objects, such as, for instance, the Arthropoda frequently 

 present. 



GRENACHER'S formula (Arch.f. mik. Anat.jX.vi, 1879, p. 468). 

 To 50 cubic centimetres of alcohol (60 to 80 per cent.) add 

 3 to 4 drops of hydrochloric acid and a knife-pointful of 

 powdered carmine. Boil for ten minutes. When cool, filter. 



The solution may or may not be now ready for use ; this 

 depends on the proportions of acid and carmine used, and 

 these proportions cannot be exactly prescribed on account of 

 the variability of commercial carmine. If the solution is found 

 to give in five or ten minutes a diffuse stain (like a borax-car- 

 mine stain, see No. 163), more hydrochloric acid must be 

 cautiously added drop by drop, and the solution tested with 

 fresh sections until the desired effect is produced. If after 

 some days (or at once) the solution gets a yellow hue, it is a 

 sign that too much HC1 has been used, and the excess must 

 be neutralised by cautious addition of ammonia, which will 

 restore the purple tint of the solution. 



This is, generally speaking, a nuclear stain. Over-staining 

 and diffusion, should either happen, may be corrected by wash- 

 ing out with alcohol very slightly acidulated with HC1. Sections 

 must always be washed in alcohol, not water ; and alcohol, not 

 water, must be used for diluting it. Dilute solutions often 

 give results different from those given by concentrated solu- 

 tions. 



The foregoing method of preparation will be found trouble- 

 some by those who are not expert at neutralising. The follow- 

 ing method, due to PAUL MAYER (quoted from GARBINI'S Manuale 

 per la Technica moderna del Microscopic, first ed., p. 46), is easy 

 and gives excellent results. Take 100 gr, of alcohol (either 



