132 BACTERIOLOGY. 



twenty-four to thirty-six hours will be a pure culture 

 of the organisms of which the colony was composed. 



Cultures of this form are not only useful as a means 

 of preserving the different organisms with which we may 

 be working, but serve also to bring out certain charac- 

 teristics of different organisms when grown in this way. 



If gelatin be employed and the organism which has 

 been introduced into it possesses the power of bringing 

 about liquefaction, it will soon be discovered that this 

 result is by no means of the same appearance for all 

 organisms. Some organisms cause a liquefaction which 

 spreads across the whole upper surface of the gelatin and 

 continues gradually downward ; again it occurs in a 

 funnel shape, the broad end of the funnel being upper- 

 most and the point downward, corresponding to the 

 track of the needle. At times a stocking- or sac- formed 

 liquefaction may be noticed. 



NOTE. Obtain a number of organisms from different 

 sources in pure cultures by the method given. Plant 

 them as pure cultures, all at the same time, in gelatin 

 preferably gelatin of the same making retain them 

 under the same conditions of temperature, and sketch 

 the finer differences in the way in which liquefaction 

 occurs. 



