200 THE MICROSCOPICAL NEWS. 
No one staining material, nor any single method of procedure 
can be made to answer well these requirements for all kinds of 
bacteria, and in spite of successful practice upon many kinds, the 
operator must ever be prepared for failure in some one or more of 
the specified particulars. Still, the failures after a little experience 
may be accounted the exceptions and success the rule. 
Except for a few special results, aniline dyes are by far the most 
serviceable in staining bacteria ; but these dyes are very different 
in their effects, and require different treatment. Probably an 
aqueous solution of methyl violet, so commonly used as ink, has 
been more generally used for the detection and examination of 
bacteria than any other agent, though in the hands of some of the 
most skillful workers gentian violet and methylene blue have each 
been pronounced most highly serviceable for general purposes. 
Ordinary violet is, when effective, usually quick and intense, and 
there is from the aqueous solution no sedimentary deposits conse- 
quent upon evaporation or subsequent washing with water, and most 
often the colour of the mass can be suitably reduced by causing a 
stream of water to play from a wash bottle upon the material. 
There are, however, two objections to this stain, aside from the in- 
stances in which it entirely fails to colour the objects. It is not 
suited for photography, and it is apt to be very fleeting, especially 
if exposed to the light. For the first there is no remedy, but for 
the second something can be done. ‘The stronger the dye or the 
longer its application, especially the former, the more permanent 
the colour, and sufficient washing may be practised to secure the 
required tint of the field. After, however, the use of the dye of 
any strength, the application of alcohol is sure to discharge the 
colour from everything ; hence mounting in balsam is considered 
impossible. ‘Treated with acetate of potash, the colour is more 
stable and holds good for some months, but gradually fades in most 
cases. I have recently used instead of the aqueous solution of this 
violet aniline a solution in glycerine, with, so far, very satisfactory 
results. This may not be new to others—probably is not—but 
was to myself when first tried, about two months ago. After my 
experience with the aqueous solution, I was surprised to witness 
the permanence of the stain under treatment with alcohol and of 
exposure to full sunshine for several days. The preparations are 
still in good condition, though nothing further can now be stated as 
to the length of time they will so remain. The aniline is soluble in 
glycerine to any extent, as is the case with most of the other aniline 
colours tried, and was used of a strength of about one to five in 
bulk. To this may be added a small quantity of pure carbolic 
acid without detriment, so far as observed, and with advantage in 
the way of effectiveness in some cases. There is no difficulty 
whatever in passing the stained material through alcohol and ben- 
