92 BACTERIA 



found that the optimum temperature is from 30 to 35 C., 

 but that the microbe will flourish between 5 and 40 C. 



Although fully-formed Bacteria, like other organisms, are 

 usually killed by exposure to heat several degrees below 

 boiling-point, yet the spores of some species will withstand, 

 at any rate for a limited time, a much higher temperature 

 even as high as i3oC. On the other hand, putrefactive 

 Bacteria retain their power of development after being exposed 

 to a temperature of mC., although during the time 

 of exposure all vital activity is of course suspended. 



Bacteria also resemble other organisms in being unable 

 to carry on active life without a due supply of water : no 

 perfectly dry substance ever putrefies. The preservation for 

 ages of the dried bodies of animals in such countries as 

 Egypt and Peru depends at least as much upon the moisture- 

 less air as upon the antiseptics used in embalming. 



For the most part Bacteria are unaffected by light, since 

 they grow equally well in darkness and in ordinary daylight. 

 Many of them, however, will not bear prolonged exposure to 

 direct sunlight, and it has been found possible to arrest the 

 putrefaction of an organic infusion by insolation, or exposure 

 to the direct action of the sun's rays. It has also been 

 proved that it is the light-rays and not the heat-rays which 

 are thus prejudicial to the life of micro-organisms. 



