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 (i) 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 



