312 PHYSIOLOGY OF BACTERIA 



cause of death. Cells without food live longer when 

 dried; dry cells live longest at the lowest temperatures; 

 dry and cold cells live longest in the absence of oxygen; 

 but they do not live indefinitely, and the cause of death 

 under these circumstances, though unknown, is of 

 general biological interest. 



The laws of the death of dry bacteria apply also to 

 bacteria in non-aqueous liquids. Bartlett and Kinne 

 (1913) compared the resistance of spores heated in water, 

 glycerol, olive oil, cottonseed oil and paraffine, and 

 found the bacteria in non-aqueous liquids much more 

 resistant. Staphylococci were killed quickly at 100°C. 

 in all media, lower temperatures not being tried. Spores 

 of B. anthracis or B. suhtilis at lOC'C. died in water in 

 a few minutes, but were still alive in glycerol after 

 seventy-five minutes, in oil after fifty minutes. Spores 

 of B. vitalis survived 120°C. (15 pounds pressure) in 

 water ten minutes, in glycerol 90 minutes, and in oil 

 two hours, but not longer. This again indicates that 

 the death process by dry heat is entirely different in its 

 nature from that by moist heat. 



(d) SUMMARY OF FACTS 



Dry bacteria die slowly, and there is a fairly definite 

 order of death. The rate of dying varies greatly, even 

 with the same culture dried on different days. 



Dry bacteria die more rapidly in air than in a vacuum, 

 or in an inert gas; they die more rapidly in an oxygen 

 atmosphere than in air. Oxygen is the most essential 

 cause of death of dry bacteria. 



Dry bacteria die more rapidly at higher temperatures. 



Dry bacteria probably die more rapidly when their 

 moisture content is high. 



