112 Biological Stains 



possibly hematoxylin; and for this reason was the first dye to be 

 given a thorough investigation by the Commission. It is used: 

 first, as a nuclear stain in histology, for which purpose its strongly 

 basic character as well as the ease with which it can be applied 

 without over-staining, make it quite valuable; second, as a bacte- 

 rial stain, notably in milk work and in the diagnosis of diphtheria, 

 where it is especially useful because it has an aflSnity for the bac- 

 terial protoplasm as great as that of the rosanilin dyes, but is less 

 intense, more selective in its action and more subject to differen- 

 tiation; third, in the vital staining of nervous tissue, where a non- 

 toxic, basic dye is needed; fourth, in combination with eosin in the 

 blood stains, thanks to the ease with which it can be partly con- 

 verted into lower homologs such as the azures, and thus acquire 

 polychrome properties; fifth, as an oxidation-reduction indicator, 

 particularly in milk; and lastly, as an indicator in the Levine 

 eosin-methylene-blue medium for differentiating the colon and 

 aerogenes organisms. 



It can be readily understood that an especially pure product is 

 needed when the dye is to be used for vital staining or in blood 

 work. For vital staining the U. S. P. zinc-free dye is always rec- 

 ommended, sometimes with even further purification ; although the 

 investigations carried on by the Commission indicate that the U. 

 S. P. product is sufficiently pure. For blood work some companies 

 sell a "methylene blue rectified for blood stains." This grade, 

 however, is generally less pure than the medicinal or U. S. P. 

 grade, and there seems no reason for specifying it. The same is 

 true of various other grades such as those denoted BX, BG, etc., 

 which are ordinarily purer than the textile dye, but less pure than 

 the medicinal grade. 



In former years, one or both of the German stain companies sold 

 a grade designated "methylene blue for bacilli". This was often 

 erroneously assumed to be specially adapted for staining bacteria. 

 As a matter of fact, it proved to be the zmc salt, quite impure, and 

 was probably labelled under the specified designation because it 

 was not considered good enough for any other purpose ! Even for 

 staining bacteria it did not prove especially satisfactory. (It is, 

 among other things, almost insoluble in alcohol, and cannot be 

 used in any formula — such as that of Loeffler — which is derived 

 from a stock alcoholic solution of the dye.) At present the Ameri- 

 can manufacturers, at least, have wisely discontinued the sale of 

 the zinc salt under this designation. One American concern, 

 however, still sells a "methylene blue for bacilli", but it is entirely 

 different from the former imported product of that name. It is 

 apparently methylene blue chloride, less pure than the medicinal 

 grade but entirely satisfactory for staining bacteria and for many 

 other staining purposes. The Commission has been unable, how- 

 ever, to find that it has any special advantages over the medicinal 



