Q2 METHODS USED IN THE STUDY OF BACTERIA 



tures are of the greatest value since minute differences in 

 culture characters are revealed. Agar, potato, blood serum, 

 and, occasionally, gelatin are prepared with a sloped surface, 

 and cultures are made on the surface of these known as streak 

 cultures, in which the bacteria are sown on a streak made by 

 the platinum needle by drawing it the full length of the sloped 

 (see Fig. 30) surface. Fluid cultures in bouillon, Dunham's 

 solution, milk, etc., are frequently used. Bacteria are some- 

 times grown in mass cultures for special purposes, particularly 

 in bouillon for the production of the toxins. A great many 

 attempts have been made to make permanent preparations 

 of bacterial cultures. The attempts, however, have been 

 largely unsuccessful since the cultures fade in color and 

 otherwise change in a relatively short time. 



