98 



INFLUENCE OF TEMPERATURE ON BACTERIA 



range of temperature at which saprophytic bacteria, including soil 

 organisms, may develop is usually a far wider one. These points 

 are well illustrated by the following table taken from Fischer: 



The fatal temperature may be even somewhat higher than this. 

 It will vary with a number of factors, the condition of the organism 

 playing a great part. For instance, Duclaux found that certain 

 bacilli (Tyrothrix) found in cheese are killed in one minute at a 

 temperature of from 80 to 90 C., whereas for the spores of the same 

 bacillus a temperature of from 105 C. to 120 C. was required. 



Duclaux considers it erroneus to speak of a definite temperature 

 as a fatal one; instead he considers it better to speak of it as deadly. 

 This is due to the fact that the length of time an organism is exposed 

 to a high temperature is important. This is illustrated by the experi- 

 ments of Christen on the spores of the bacilli of the soil and of hay. 

 The spores were exposed to a stream of steam and the time noted 

 which was necessary to kill the spores at the various temperatures. 



Temperature. 



100 

 105-110 



115 

 125-130 



135 



140 



Time reqired to kill spores. 

 over 16 hours. 

 2 to 4 hours. 

 30 to 60 minutes. 

 5 minutes or more. 

 1 to 5 minutes. 

 1 minute. 



Moist heat is much more effective as a germicide than is dry 

 heat. The probable explanation of this is that where dry heat is 

 applied it must be high enough to decompose the organic constit- 

 uents of the cell, the proteinaceous substance being in the form of 

 the anhydride which can, in the presence of moisture, take up water 

 according to the following equation: 



HN R COH N RCO + H 2 O = H 2 N RCOH N R COOH 



Two or more molecules of this hydrated protein would then con- 

 dense with the formation of the non-reversible gel. 



2H 2 NRCOHNRCOOH = H 2 N R COH N R COH N R COH NR 



COHNR COOH + H 2 O 



