86 
PRINCIPLES OF BACTERIOLOGY 
for it is my conviction that no directions will ever do any 
good; the pupil must be individually taught just how 
to handle the microscope and care for it. 
Special Staining Methods 
A. Gram’s Method. —This is an extremely important 
method which permits differentiation of bacteria into two 
classes: the so-called Gram-positive and Gram-negative 
bacteria; this will be made clear immediately after the 
Fig. 16.—Microscope (A) and artificial illumination (B). 
description of the method of staining which is as fol¬ 
lows : 
1. Prepare the bacterial smear in the usual manner on 
a glass slide or a cover-glass, as described in the section 
on the Study of Bacteria in Living State. 
2. Cover the preparation for five minutes with the 
anilin gentian violet stain, which is prepared as follows: 
5 c.c. of anilin is shaken thoroughly with 125 c.c. of dis- 
