PLASMA STAINS 167 



through the alcohol into xylol as quickly as possible in order 

 to avoid any extraction of the methyl green, which easily comes 

 away in the alcohol. Druner [Jena Zeit., xxix, 1894, p. 276) 

 stains for ten minutes in the concentrated solution, treats for one 

 minute with alcohol containing 0-1 per cent, of hydrochloric acid, 

 and then with neutral alcohol. 



The best results are obtained with sublimate material ; chrome- 

 osmium material, and the like, give a much inferior stain. Pre- 

 parations made with the usual mixture, as given above, are liable 

 to fade ; by acidifying the mixture a stronger and more sharply 

 selective stain is obtained, which does not fade. IJut too much 

 acid nmst not be added. According to the Enzyk. mik. Technik, 

 you may add 15 to 24 drops of 0-2 per cent, acetic acid to 100 

 c.c. of the diluted solution. 



Another process of acidification is given by M. Heidenhain (Ueber 

 Kern und Protoplasma, p. 116) ; for this see fourth edition. See also 

 Israel (Prakticum Path. Hist., 2 Aufl., Berlin, 1893, p. 69) ; Trambusti 

 (Ricerche Lab. Anat. Roma, v, 1896, p. 82 ; Zeit. wiss. Mik., xiii, 1896, 

 p. 357) ; and Thome (op. cit. supra). Eisen (Proc. Calif. Acad. (3), i, 

 1897, p. 8) acidifies with oxalic acid. 



After acidification the solution must not be filtered, and if it has been 

 kept for some time a little more acid must be added. 



Before staining (M. Heidenhain, toe. cit.), sections should be treated 

 for a couple of hours with 1 per cent, acetic acid, then for ten to 

 fifteen minutes with ofiieinal tincture of iodine, and be rinsed with 

 alcohol before bringing into the stain. The treatment with acid is 

 necessary in order to ensure having the sections acid on mounting in 

 balsam. The primary object of the iodine is to remove any sublimate 

 from the preparations, but it also is said to enhance the power of stain- 

 ing of the chromatin with methyl green, and to produce a more selective 

 staining of protoplasmic elements. 



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

 capricious. The correct result should be a precise chromatin stain 

 combined with a precise stain of the 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. It is difficult to dehydrate the sections without 

 losing the methyl green. 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 [i. in thickness, and if they are over 5 the desired 

 results are almost hopeless. The stain keeps very badly. Lee stated 

 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 ground cytoplasm for which Martin Heidenhain employed 

 the mixture ; for the study of gland cells ; and for similar objects. But 

 to recommend it, as has been done, as a general stain for ordinarj^ work, 

 is nothing but mischievous exaggeration. For it is far from having the 

 qualities that should be possessed by a normal section stain. Workers 

 have at length found this out, and it is now but little used except for 

 the special purposes above indicated. 



323. Ehrlich's " Triacid " Mixture. This name would seem 

 to indicate that the mixture contains three " acid " colours, 



