308 W. A. WALL AND A. H. EOBERTSON 



dissolve the milk preparations, may render them satisfactory for 

 use. 



Methylene blue for bacterial stains comes on the market both 

 as a zinc double salt and as a zinc-free hj'^drochloride. Methyl- 

 ene blue "for bacilU" is generally the zinc salt but may contain 

 various quantities of the free hydrochloride. The pure hj'^dro- 

 chloride is a dark greenish-blue crystal and is handled under the 

 trade names of "Medicinal" or "U. S. P. " A solution of the 

 pure hydrochloride usually gives a dark blue stain to dried films 

 of milk which becomes deeper the longer the preparation is left 

 in the solution. The deep blue of the casein can be taken out 

 by decolorizing with alcohol. The bacteria do not lose their 

 stain as rapidly as the casein, thus making it possible to prepare 

 a good preparation \\'ith this form of methylene blue. Methy- 

 lene blue "for bacilli," which may be the pure zinc salt but may 

 contain certain amounts of the free hydrochloride, may be any 

 color from a greyish-red to a reddish-blue. An aqueous solution 

 of the zinc salt will stain satisfactorily; but it is insoluble in 

 alcohol and cannot be used in the Loeffler formula. Usually 

 decolorization with alcohol is unnecessary with zinc salt solutions. 

 An aqueous solution of the zinc salt which contains very Uttle 

 or none of the pure hj^drochloride may possibly cause the washed 

 out appearance mentioned in the Committee report. 



Aqueous staining solutions frequently become grossly contam- 

 inated with bacteria and molds, so much so that organisms 

 from this source may be found on the smears stained in these 

 solutions. To avoid this difficulty Loeffler's alkaUne methylene 

 blue has been tried with uniformly good results. Later it was 

 found that any solution of methylene blue prepared in 30 per 

 cent alcohol was as satisfactory as the Loeffler's formula, and 

 also prevented the growth of organisms in the staining solution. 

 These results indicate that stains prepared m alcohoUc solutions 

 are to be preferred to the aqueous solutions recommended in the 

 Standard Methods Report; but on account of the insolubiUty 

 of the zinc salt in alcohol, either the medicinal methylene blue 

 or some methylene blue "for bacilli" wliich is not largely made 

 up of the zinc salt must be used. 



