CHAPTER Vt. 
CULTURES OF BACTERIA. 
OWING to their small size and to their similarity 
of form, the different species of bacteria cannot be 
recognized by microscopic examination alone. Re- 
course must be had to a study of their biologic 
peculiarities. For this purpose it is necessary to 
grow them on artificial culture-media. If a single 
germ is planted on a suitable nutrient medium, 
and is protected from contamination, it multiplies 
rapidly and forms a colony. Such a colony is com- 
posed of but one species, since all its members are 
the descendants of a single germ. Cultures made 
from such a colony are known as ‘‘ pure cultures,”’ 
since they contain but one species. From a study 
of the behavior of these pure cultures, under differ- 
ent conditions, the diagnostic characters of the 
species are determined. 
I. BOUILLON CULTURES. 
1. Inoculate a tube of bouillon by touching the 
culture to be studied with a sterile platinum needle, 
and then dipping the needle in the bouillon. 
2. Place at the room-temperature or in the incu- 
bator, and examine from day to day, and note any 
changes as follows : 
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