360 LETHE E. MORRISON AND FRED W. TANNER 



bacteria, those that develop at room temperature, about 20°C., 

 and have their optimum temperature at about 50°C., and their 

 maximum temperature at about 60°C. 



It would seem to be indispensable to fix clearlj' the limits within 

 which the term thermophilic bacteria should apply. Some divi- 

 sion evidently must be made in this group of organisms that grow 

 at such widely differing ranges of temperature. The division 

 made by Bergey into true thermophiles and facultative ther- 

 mophiles seems to be the most tenable up to the present time. 

 Further work on temperature relations of these thermophiles is 

 being carried out in this laboratorj^ and perhaps when the data 

 from this investigation are available a better differentiation will 

 be possible. 



Of the 52 waters from which thermophiUc bacteria were isolated 

 44 (almost 85 per cent) were condemned for the presence of B. 

 coll of fecal origin. Tliis fact suggests a possible sanitarj^ signifi- 

 cance of thermophiHc bacteria in water analysis. The data are 

 insufficient to draw any definite conclusions on this subject but it 

 is a subject worthy of investigation. A similar suggestion was 

 made by Brazzola (1906) when he stated that he thought the 

 thermophiles were of very great importance in the study of 

 the potability of water. 



VI. CONCLUSIONS 



1. The aerobic thermopliilic bacteria studied in this investiga- 

 tion seemed to make up a closely related group when the salient 

 characters only are considered. 



2. All strains form spores and are strongly proteolytic which, 

 in connection with their temperature relations, makes them of 

 importance in food preservation. 



3. Thermophilic bacteria are widely distributed in nature (soil, 

 water, etc.) and thus may cause serious losses in those industries 

 where high temperatures are used for controlling bacterial 

 development. 



4. The abiUty of thermophilic bacteria to grow at high tem- 

 peratures may be due to a particular property of the protoplasm 

 (water content?). 



