182 CHAPTER XIII. 



tion to the chromatin stain, which is not the case with 

 sublimate material. 



The stain is fairly permanent in balsam, but is very liable 

 to fade a little, and may fade a great deal. If acids have 

 been used after staining, great care should be taken to wash 

 them out thoroughly before mounting. In aqueous media the 

 stain cannot be relied on to keep (this refers to the old solu- 

 tions : MAYER finds that his haematein preparations have kept 

 well for at least some months in glycerin, if not acid, and, 

 with certain precautions, in balsam). Turpentine-balsam 

 should not be used (Mayer, in litt.}. 



237. General Remarks. We have the coal-tar colours for 

 staining sections, and we have carmine and cochineal for 

 staining in bulk. What, then, do we want haematein for ? 

 The answer is that we sometimes want it for staining, either 

 sections or in the mass, on account of the faculty it has of 

 staining tissues that have been treated with chromic and 

 osmic mixtures. This it does in general better than any 

 carmine or cochineal, and sometimes better than any of the 

 coal-tar colours. It is also a more powerful stain than car- 

 mine ; and according to the mode of employment affords 

 either a chromatin stain or a sometimes valuable plasma- 

 stain. The chief haematein or haematoxylin plasma-stains 

 are found not amongst the alum-haematein lakes, but amongst 

 the other compounds, iron or chrome compounds, etc. 



A. Alumina-hsematein Lakes. 



238. MAYER'S Haemalum (MAYEK, Mittli. Zool. Stat. Neapel, 

 x, 1, 1891, p. 172). One grm. of the colouring matter 

 (either haematein or the ammonia salt, 234, 235) dissolved 

 with heat in 50 c.c. of 90 per cent, alcohol, and added to a 

 solution of 50 gr. of alum in a litre of distilled water. Allow 

 the mixture to cool and settle, and filter if necessary. Or 

 more recently (Grundziige, p. 152), instead of dissolving the 

 haematein or salt in alcohol, Mayer rubs it up in a mortar 

 with a very little glycerin. 



It is not necessary to conform exactly to the proportions given, and a 

 rough and ready hsemalum solution may be at any time extemporised by 

 adding a few drops of alcoholic solution of hjematein to an alum solution of 

 any desired strength. 



