94 COCHINEAL AND OTHER ORGANIC STAINS. 



In general, freshly prepared solutions stain badly and dif- 

 fusely ; they ought to be allowed to " ripen " 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 precipitating, 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, but this is not favorable to 

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

 re-neutralise afterwards with ammonia. 



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. In aqueous media 

 it cannot be relied on to keep. 



Hgematoxylin 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. KEAUSE, Intern. 

 Zeit.f. Anai. u. Hist., i, 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. This effect is 

 more especially obtained with solutions in which the proportion of alum is 

 less than a third of the extract of logwood employed. 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. 



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 

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

 reaction is not obtained with glycerin mounts. 



Aqueous solutions. 



174. Delafeld's Hamiatoxylin. (Zeit. f. wiss. Mik., ii, 1885, p. 288. 

 The history of this formula is as follows : It had long been in use in the 

 Institute of Pathology at Heidelberg, when it was communicated by Pfitzner 

 to Flemming, who published it and particularly recommended it, in his 

 Zellstz., &c., p. 388, 1882). Flemming then attributed the formula to 

 Grenacher, and in consequence the stain went for years by the name of 

 "Grenacher's hcematoxylin." Later on, Flemming discovered that this 

 attribution was erroneous, and attributed the formula to Prudden ; and in 

 consequence it was thenceforth known for some time as " Prudden's haema- 



