THE PREPARATION OF CERTAIN SPECIAL MEDIA 39 



EXERCISE X 



THE PREPARATION OF CERTAIN DIFFERENTIAL AND 

 SPECIAL MEDIA 



52. In studying the properties of bacteria it is desirable to 

 cultivate them on a number of different media. Bouillon, agar, 

 and gelatin are most commonly used, but others are neces- 

 sary in determining the cultural peculiarities and important 

 biochemic properties of the organism in question. The culti- 

 vation of bacteria upon these media may be regarded in the 

 light of a test to determine the presence or absence of certain 

 properties or powers possessed by the bacterium in question : 

 thus, for example, whether the species in hand will coagulate 

 the casein in milk, produce gas in media containing saccha- 

 rose, grow on potato, etc. The number of these tests which 

 have been used and recognized as important is quite large, 

 but in a short course only those possessed of special differen- 

 tial value can be tried. In describing a new species or iden- 

 tifying any of the carefully described ones, it is important to 

 know at least some of these cultural peculiarities and biochemic 

 properties. For this reason it is necessary to learn the method 

 of preparation and the use of certain of these media. The 

 more important of such media are included in this exercise. 



In addition to the above, a few species of bacteria require 

 particular kinds of media for their diagnostic or most differ- 

 ential growth. Among these are the specific organisms of 

 glanders, diphtheria, and tuberculosis. The preparation of 

 these particular media will be considered in connection with 

 the study of the organisms requiring them. 



53. Work for this exercise. Prepare for culture media 

 5 tubes of potato, 5 tubes of milk, 5 tubes of litmus milk, 

 5 tubes of glucose agar, 5 tubes of glycerin agar, 3 fermenta- 

 tion and 5 small test tubes of bouillon containing glucose, the 



