STUDIES ON THERMOPHILIC BACTERIA. I 345 



IV. EXPERIMENTAL 



Sources of ciiUures. The present investigation has been hmited 

 to a study of some of the characteristies of 52 cultures of aerobic 

 thermophilic bacteria from water; a more detailed study of forms 

 from other sources is now being made. The cultures of ther- 

 mophilic bacteria used in this investigation were isolated from 

 samples of water furnished by the Illinois State Water Survey. 

 Permission to use the samples was obtained from Professor E. 

 Bartow, while director of the Water Survey. These samples 

 came from different places in the state of IlUnois and had been 

 collected and shipped to the Water Survey according to directions 

 furnished by them. 



^lany types of waters from different sources including deep 

 wells, shallow wells, drilled wells, dug wells, springs, raw and 

 treated municipal supplies and springs were used. In this manner 

 it was possible to carry on a more representative study than if 

 the samples had been taken from a restricted area. Out of 224 

 samples of water, 60 were found to contain thermophilic bacteria 

 according to the method adopted for their isolation. This is to 

 be regarded as a minimum for it is believed that thermophiles are 

 quite abundant in nature and many samples wliich were negar 

 tive when 1-cc. portions were examined would probably have 

 been positive had a larger amount been used. 



Method of isolation. Agar plates were poured in the usual way 

 using 1-cc. and 0.1-cc. portions of the samples; the plates were 

 incubated at 55°C. for twenty-four hours. Most of the ther- 

 mophiles grow very rapidly at 55°C. and a longer incubation 

 period was unnecessary. Any colonies that had developed in 

 that length of time were transferred to agar slants; later it was 

 found that it was easier to keep the cultures in broth since agar 

 dried so quickly at 55°C. Control plates and agar plates that 

 had been exposed to the air of the laboratory were incubated 

 under the same conditions, but in no case was there any growth of 

 thermophiles shown, either from the agar itself or from the air 

 of the laboratory. 



