GENERAL BACTERIOLOGY 
91 
By this method the tubercle bacilli are stained red, 
while everything else (including other bacteria) is stained 
blue. 
The principle of this stain is as follows: the tubercle 
bacilli do not stain with ordinary dyes—for this reason, 
hot carbol-fuchsin is used; but other bacteria which may 
be present (in the sputum, urine, etc.) are also stained 
(red). When strong decolorizing acid is applied, how¬ 
ever, all other bacteria lose the carbol-fuchsin stain, and 
take the methylene blue, while the tubercle bacillus does 
not give up the carbol fuchsin in spite of the action of 
the strong acid solutions (for this reason it is called an 
“acid-fast” organism), and remains red. Other acid- 
fast bacteria are the smegma and the leprosy bacilli. 
Pappenheim’s Method 
This is used in order to differentiate between the 
tubercle and the smegma bacilli, which are stained 
alike; this is especially important in the examination of 
urine, as smegma bacilli, derived from the genitals, may 
be the source of confusion. 
Preparations are made in the usual way: Stain with 
hot carbol fuchsin for two minutes. Pour off the stain 
without washing, and pour on the following mixture: 
Rosolic Acid .1 gram. 
Absolute Alsohol .100 c.c. 
Methylene-blue .to saturation. 
Glycerine .20 c.c. 
This is poured on and drained off slowly, four or five 
times, then washed in water. 
In this way the smegma bacilli are decolorized, while 
the tubercle bacilli are stained bright red. 
F. Stain for Malaria and Blood Films. —The best one 
is Wright’s stain; which is prepared as follows (avoid 
using the commercial stain, as the various specimens vary 
