154 BACTERIOLOGY. 
desired). Ora few drops of the dye may be held upon the cover glass 
itself, and if heat is necessary the solution of dye may be heated 
in this position by holding it just over a flame. After the dye has 
acted sufficiently the whole is rinsed in water, and if necessary may be 
decolorized in any solution desired. The specimen is then dried and 
mounted, specimen side down, in water, glycerine or Canada balsam, 
upon a glass slide. 
How are tissues prepared for bacteriological examination ? 
First, the tissue is cut into small cubes which are placed in absolute 
alcohol for a few days in order that it may become hard and firm 
enough to cut. It is then fixed upon a cork or block of wood, the best 
cementing agent being a fairly thick solution of celloidin in equal parts 
of alcohol and ether. After having been in alcohol a number of hours 
this cement becomes firm and the specimen is ready to cut. This may 
be done either with an ordinary razor or with a microtome. The 
microtome has a movable holder carrying the specimen, and a block 
moving upon a smooth track, which carries a razor-blade. With this 
apparatus (a full description of which is out of place here) thinner and 
more even sections can be cut than with an ordinary razor. With 
either method both the specimen and razor must be kept constantly 
wet with alcohol in order that the thin sections of tissue may hold 
together. 
What dyes may be used in staining bacteria in tissue ? 
The ordinary aniline dyes may be used, or gentian violet according 
to Gram’s method spoken of before, or Léffler's solution of methylin 
blue. The two latter give the best results. 
Give in their proper order the steps for staining bacteria in tissue. 
1. The sections which are kept in alcohol are put into distilled water 
1 minute. 
. Staining solution, 4 to 5 minutes. 
. Water, 2 to 3 minutes. 
0.01 per cent, watery solution of acetic acid, 4 minute. 
. Alcohol for an instant. 
. Absolute alcohol for an instant. 
. Xylol, 2 minutes. 
. Transfer to a slide with a lifter and remove excess of xylol with 
blotting paper. 
9. Mount in xylol balsam. 
Ost TP Ww DO 
