56 



BACTERIOLOGY. 



few minutes by exposure to moist heat of about 70°, but the 

 spore form may resist for hours. Steam heat, which, as a 

 rule, instantly kills the vegetating- form will require 5 to 10 

 minutes, and in some instances as many hours, to destroy 

 the spore. A similar difference between the vegetating 

 and spore form will be observed in the action of various 

 chemical substances. 



Spores will resist the action of dry heat more readily 

 than that of steam heat. A dry heat of 140° may require 

 an hour or more to destroy spores which would be killed in 

 a few minutes by exposure to steam. Heat and moisture are 

 therefore more destructive than heat alone. This is equally 

 true for the higher forms of life. Thus, in a very dry cli- 

 mate man can endure without discomfort a temperature of 

 130-140° F. whereas a much lower temperature in the pres- 

 ence of moisture is prostrating. 



Steam heat under pressure will destroy spores more 

 readily than will ordinary steam heat. The spores of a 

 •certain potato bacillus, which resist steam for 5-6 hours, 

 are destroyed in 10 minutes by an exposure to steam under 

 pressure at a temperature of 120°. 



The spores of different species possess different degrees 

 of resistance. Thus, the anthrax spores are more easily 

 destroyed than those of the hay bacillus. Again, the seve- 

 ral varieties of a given species may produce spores which 

 will show extreme variation in resistance. There are an- 

 thrax spores which are readily destroyed by 5 per cent, car- 

 bolic acid within 24 hours, whereas other anthrax spores 

 may not be affected by an exposure of 40 or 50 days to this 

 solution. 



The extreme resistance of some spores, as briefly indi- 

 cated above, accounts for the theory of spontaneous 

 generation which at one time was quite universally accept- 

 ed. According to this theory it was supposed that the 

 lower forms of animal and plant life could develop without 



