CONCERNING HJ1MATEIN. 117 



preparations in balsam, and expose them for some time to the light. The 

 reaction is not obtained with glycerin mounts. 



In order to get a blue stain in preparations that have come 

 out red through the acidity of the staining bath, it is usual to 

 treat them with weak ammonia, in the belief that the blue 

 colour is restored by neutralisation of the acid that is the 

 cause of the redness. According to MAYEE, the ammonia 

 acts not by neutralising the acid, but by precipitating the 

 alumina, which carries down the hgematein with it (if 110 

 alumina were present the colour would be purple, not blue). 

 The same result can sometimes be obtained by merely washing 

 out with common tap-water, which is usually sufficiently 

 alkaline, and can be obtained with certainty by treatment, with 

 bicarbonate of soda or acetate of soda or potash. And this 

 is the preferable course, as ammonia is certainly a dangerous 

 thing to treat delicate tissues with. Of course this is a dif- 

 ferent question from that of neutralising with an alkali tissues 

 that have been treated with an acid to correct over-staining. 

 Here the neutralisation may be indicated in the interest of 

 the preservation of the stain, or of the tissues themselves. 



179. Concerning Hsematein. The following is taken from the 

 two papers of Mayer quoted above, 144, 174. Hsematein 

 occurs as a dark green metallic mass, red by transmitted light, 

 which may be rubbed up into a violet powder or small red 

 crystals. It is entirely, though with difficulty, soluble in 

 distilled water and in alcohol, giving a yellowish-brown 

 solution, which remains clear on addition of acetic acid. 

 Alkalies dissolve it with a blue-violet tint. 



It is now found in commerce ; but Mayer has hitherto only 

 been able to procure it in a pure state from G-EIGY AND Co., 

 in Bale. But there is also found in commerce an ammonia- 

 compound of haematein Hdematein-Ammoniak, also known 

 in commerce as Haematemum crystallisation; this may be 

 obtained in a sufficiently pure state from E. MERCK, of 

 Darmstadt. 



This is somewhat more easily soluble in both water and 

 alcohol than hsematein is, and does quite as well for staining 

 purposes. The histologist can easily prepare it for himself as 

 follows : 



Dissolve 1 grm. of haematoxylm with the aid of heat in 20 



