116 HJBMATBIN AND OTHER ORGANIC STAINS. 



It has been explained above that when freshly prepared 

 they stain badly and diffusely ; they ought either to be 

 "ripened" by Unna's method( 175) or to be allowed to 

 " ripen" spontaneously before use. This takes, according to 

 the nature of the solution, a few hours, or days, or months. 

 On the other hand, kept solutions easily go bad by precipi- 

 tating, or becoming acid, or becoming mouldy. 



Most of the solutions, when in good staining order, have a 

 great tendency to over-stain. Over-stains may be corrected 

 by washing out with weak acids (e. g. (H to O2 or even 0*5 

 per cent, of hydrochloric acid), but this is not favorable to 

 the permanence of the stain. If acids be used, it is well to 

 re-neutralise afterwards with ammonia or bicarbonate of 

 soda (O'l per cent.). 



A better plan is, perhaps, to wash out with alum solution ; 

 but this frequently requires great patience. 



The stain is fairly permanent in balsam, but is sure 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 solutions : 

 Mayer finds that his haematein preparations have kept well 

 both in aqueous media and, with certain precautions, in 

 balsam). 



178. HaBmatoxyliii stains in different tones of blue or of red, 

 according to the composition of the staining solution. 



According to WATNEY (see Phil Trans., 1882, p. 1075 ; KBATJSE, Intern. 

 Zeit. f. Anat. u. Hist., 5, p. 154 ; and M. FLESCH, Zeit.f. wiss. Mik., 1885, 

 p. 358, from whom I quote) the colour is an intense blue if the solution has 

 been made with freshly prepared alum, whilst a red tone is obtained if the 

 solution has been made with old alum. The reason of this is that alum 

 that has been long kept almost always contains free acid. The red solutions 

 exhibit a great affinity for connective tissue, and for the granules of "plasma- 

 cells ; " whilst the blue solutions show a special affinity for mucin and 

 chromatin. MAYER (Mitth. Zool Stat. Neapel, 10, i, 1891, p. 177) has a 

 different explanation of this reaction. He finds that solutions containing 

 only hsematein and aluminium chloride stain mucin with special energy ; 

 whilst solutions which also contain from 10 to 20 per cent, of magnesium 

 chloride, nitrate of ammonia, chloride of lithium or of calcium, of sodium, 

 or of ammonium, do not do so, but are pure nuclear stains. 



It has been discovered by LANGHANS (see MAX FLESCH, loc. cit.) that it is 

 possible to obtain these two elective reactions with one and the same solution. 

 All that is necessary is to stain with the solution of Delafield, mount the 



