432 BACTE&IOLOGY. 



gelatin after the agar is thoroughly melted, so as not 

 to alter this ingredient by prolonged exposure to high 

 temperature. The glucose is added after clearing. 

 The medium must contain 1.5 per cent, of normal 

 acid. 



Growth of the Colonies. The growth of the typhoid 

 bacilli in plates made from the medium as above de- 

 scribed gives rise to small colonies with irregular out- 

 growth and fringing threads (Figs. 54 and 55). The 



FIG. 55. 



Colony of typhoid bacilli more highly magnified. (Hiss.) 



colon colonies, on the other hand, are much larger, 

 and, as a rule, are darker in color and do not form 

 threads. The growth of the typhoid bacilli in tubes 

 produces uniform clouding at 37 C. within eighteen 

 hours. The colon cultures do not give the uniform 

 clouding, and present several appearances, probably 

 dependent upon differences in the degree of their 

 motility and gas-producing properties in media. Some 

 of the varieties of the colon bacillus grow only locally 



