STAINS FOR PLASMA AND ACHROMATIC STRUCTURES. 335 



Renewed attention is called to OHLMACHER'S observations 

 on the employment of iodine or picric acid with safranin 



( ioi). 



M. HEIDENHAIN'S iron haematoxylin stain has been described, 

 197. It should be noted that the description of the results 

 given by Heidenhain applies to preparations fixed in subli- 

 mate, and will presumably not apply to chromic sections. 



639. Stains for Plasma and Achromatic Structures. Foremost 

 amongst these is the EHRLICH-BIONDI mixture, described in 

 259. To the account there given there remain to be added 

 some minutiae regarding the application of the stain to 

 cytological objects, particularly as regards the study of 

 attraction-spheres and other achromatic elements. M. 

 HEIDENHAIN (Cfber Kern und Protoplasma, Engelmann, 1892, 

 p. 116; see also Zeit.f. wiss. Mik., ix, 2, 1892, p. 202, a very 

 full report) gives the following instructions. Preparations 

 made with the usual mixture are liable to fade ; by acidifying 

 the mixture a stronger and more sharply selective stain is 

 obtained, which does not fade. But too much acid must not 

 be added, as this would cause a staining of the interfilar 

 substances. Heidenhain' s directions are as follows : 



Take some of the "commercial stock solution" (by which 

 appears to be meant the mixture as given in 259), and dilute 

 it with distilled water in the proportion of about 6 parts of 

 the mixture to 400 of water. Fill two beakers with distilled 

 water, and add to each a few drops of the diluted solution. The 

 coloured liquid thus obtained will show, at the same time, a 

 red tint owing to the rubin, a yellow tone owing to the 

 orange, and a greyish tone derived from the methyl green. 

 Now add to one of the beakers, with continual agitation, drop 

 by drop, a 1 : 500 solution of acetic acid until the colour of the 

 liquid turns to a strong crimson, the former yellow tone dis- 

 appearing, and the grey of the methyl green becoming less 

 marked. The two beakers serve as standards for the degree 

 of acidity that should be given to the staining bath. The 

 dilute solution that you made by diluting the original stock 

 solution* is now acidified with the dilute acetic acid, added 

 drop by drop with continual agitation, and from time to time 



* " Das aus der Stammlosung durch Verdiiimung gewonnene Quantum." 

 The passage is somewhat misty. 



