218 CHAPTER XVI. 



The stain is a very fine one when successful. But it is 

 very capricious, it seldom gives the same result twice running. 

 The correct result should be a precise chromatin stain com- 

 bined with a precise stain of the plastin element or reticuluni 

 of cytoplasm by the Saurefuchsin. Now the least defect or 

 excess of acidity causes the plasma stain of the Saurefuchsin 

 to become a diffuse one, instead of being sharply limited to 

 the plastin element. And the methyl green, being very 

 little resistent to alcohol, goes out of the chromatin Avith 

 such rapidity during the dehydration, that there is always 

 danger of the chromatin stain being lost altogether. For 

 this reason the stain will only work with very thin sections : 

 to be quite sure of good results, the sections should be of 

 not more than 3 /n in thickness, and if they are over five the 

 desired results are almost hopeless. The preparations keep 

 very badly ; the majority of mine, at any rate, have become 

 spoilt sooner or later, sometimes after only a few days. I 

 admit that the method has its raison d'etre for the very 

 special objects for which it was imagined, for the researches 

 on cell-granulations for which EHRLICH employed the three 

 colours, or for the researches on the plastin reticuluni of 

 cytoplasm for which MARTIN HEIDENHAIN employed the 

 mixture ; for the study of gland cells ; and for similar 

 objects. But to recommend it and to use it, as has been 

 done by many workers, as a general stain for sections, 

 applicable to ordinary work, is nothing but mischievous 

 exaggeration. Far from having the qualities that should be 

 possessed by a normal section-stain, the Ehrlich-Biondi 

 mixture is highly unfitted for ordinary work. Workers 

 have at length found this out, and, after a period of well- 

 nigh unparalleled popularity, this stain is now but little used 

 except for the special purposes above indicated. 



291. EHRLICH'S Triacid Mixture. According to a custom 

 whicji, I believe, originated with Ehrlich himself, and which 

 would, perhaps, be " better honoured in the breach than the 

 observance/' the name of Triacid (" Triacidlosung "} has 

 been given to a mixture of the same three dyes as in the 

 EHRLICH-BIONDI mixture, but in such proportions that the 

 " acid " colours therein have a larger share assigned to them. 

 The denomination is improper, for the mixture contains only 



