GENERAL BACTERIOLOGY 93 



CHAPTER IV 



SYSTEMATIC STUDY OF REPRESENTATIVE 

 NON-PATHOGENIC BACTERIA 



In making a systematic study of a bacterium it is necessary to 

 determine as many as possible of the points indicated in the previous 

 chapter (III.) ; and in the laboratory this becomes a regular rou- 

 tine procedure in the study of each germ. The organism is first 

 inoculated into a number of the standard media. These cultures are 

 frequently spoken of as a "set of cultures" and are usually com- 

 posed of the following : Gelatin and agar plates, a gelatin stab, agar 

 and potato streaks, a bouillon culture (or Dunham's sol.), a milk 

 culture and a dextrose gelatin or agar stab (or shake culture). 

 These cultures are then incubated at the proper temperature for 24 

 hours. They are then examined, described and sketched. At the 

 same time three cover-glass preparations are made, one each from 

 the agar, bouillon and gelatin cultures and stained with the follow- 

 ing dyes: agar with an aqueous solution, bouillon with Loeffler's 

 methylen blue, and the gelatin by Gram's method. The bouillon 

 culture is also examined in a hanging-drop for motility and the milk 

 culture for capsules. From these microscopical preparations the 

 morphological characters can usually be determined. The cultures 

 are again placed in the incubator and 24 hours later (48 hours after 

 inoculation) are again examined and any changes are noted and 

 sketched. The cultures are now usually kept at the temperature 

 of the room for about one week and then examined for the last 

 time. 



If the organism produces gas in dextrose media, fermentation 

 tubes should be inoculated and the rate, amount and formula of the 

 gas determined. 



The descriptions and sketches are conveniently made on the 

 charts provided on the following pages. 



