ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
269 
The process is similar to that used in dying cloth, and consists of 
two operations, (1) the mordanting, and (2) the staining. The bacteria 
are placed in a drop of water large onough to nearly cover the cover- 
glass, when they are allowed to dry spontaneously in the air. Do not 
use heat to dry the drop, as this deforms the bacteria and often destroys 
the flagella. The drying process should be watched, and as the last 
portions of water disappear the cover should be immersed in the 
mordant and allowed to soak for from two to five hours or more ; it may, 
for instance, be left in the mordant overnight. When culture ovens are 
available they may be used for drying the drop containing the bacteria, 
but they are not at all necessary to the success of the operation. After 
soaking in the mordant for the required time, the cover is transferred to 
a vessel containing water for about five minutes, to remove excess of the 
mordant, then it is taken out, drained, and then flooded with the stain. 
Steam the cover (held in the forceps) for two or three minutes over a 
lamp, but do not allow it to boil ; wash thoroughly in a stream of water, 
as the jet from a bottle, drain, and set aside to dry spontaneously. Then 
mount in balsam, preferably that for use with heat, but if using dissolved 
balsam, put a small drop of oil of cloves, turpentine or xylol in the 
centre of the cover before lowering the soft balsam. Do not attempt to 
decolorize in any way, nor to pass through alcohol and oil of cloves to 
balsam, or the flagella will not remain stained. 
The mordant is composed as follows : — tannin 30 grains, anilin oil 
12 drops, alcohol 1 fluid oz. This is the normal mordant, but some- 
tiiues I find it well to add a little sodic hydrate or hydrochloric acid, 
one or two drops to the dram, to make it alkaline or acid. A slightly 
alkaline mordant is best for the large forms Spirillum undula and Bacillus 
ulna , which are very common in putrefying water. The alcohol and 
tannin in the mordant are both fixing agents, and hence the bacteria are 
fixed without heat, and preserve their shape better than by any other 
method I have used. 
For a stain, any anilin colour, as fuchsin, methyl-violet, dahlia, 
methyl-green, &c., may be used dissolved in neutral anilin water made 
by shaking up a few drops of anilin oil in water, adding the stain and 
then caustic soda until it just begins to precipitate. Then filter and 
keep well corked. This stain only keeps for a few weeks, so that I 
recommend the following ; — Make a hot saturated solution of fuchsin in 
water, then add caustic soda until no more red precipitate is formed ; 
filter and save the red precipitate, which is the base rosanilin. A little 
of this, one or two grains, dissolved in a drop of anilin oil, will make 
about three or four drams of stain of the proper strength if shaken up 
with the water. It is often necessary to filter the stain before using. 
My best preparations are stained with fuchsin ; a large series of other 
mordants, many containing metallic salts, were tried, but after a year 
and a half’s use I still consider this the best. 
I would add as a caution to those who may use this method, do not 
expect perfect results on the first trial ; different bacteria require longer 
or shorter mordanting, and the proper conditions must bo determined 
by experiment in every case.” 
