32 LABORATORY BACTERIOLOGY 
EXERCISE IX 
THE EXAMINATION OF PLATE CULTURES AND THE 
MAKING OF SUBCULTURES FROM COLONIES 
46. In practical bacteriologic work plate cultures are made 
use of in determining (1) the number of bacteria there is in 
a given substance, (2) the different. species of bacteria pres- 
ent, and (3) the character of the growth in a colony of 
the organism in question. Other important facts, such, for 
example, as the relative number of each species of bacteria 
or the difference in the appearance of the surface and deep 
colonies, are learned through this process. The plate cul- 
ture, therefore, is one of the most important single methods 
employed in isolating and studying bacteria. 
47. Work for this exercise. Examine carefully and describe 
the plate cultures made in Exercise VIII. If the agar plates 
do not have colonies, or if the colonies are so numerous that 
they cannot be counted on any of the plates, make the cultures 
over again, and give an explanation in the notes of this exer- 
cise for the failure to obtain good results. 
Make a hanging-drop preparation from a colony from an 
agar plate and one from a colony from a gelatin plate, and 
examine them microscopically. Describe the appearance of 
the bacteria in each. 
Make a cover-glass preparation from each of the same 
colonies and stain each with carbol fuchsin. Examine each 
preparation carefully and make a drawing of a few of the 
isolated bacteria. Describe (§ 35) the appearance of the bac- 
teria in these preparations. 
Inoculate a tube of bouillon and one of agar from a well- 
isolated colony on one of the agar plates. 
48. Suggestions for the examination of the plate and roll 
cultures. Observe the general appearance of the plates; note 
