THE VITAL PHENOMENA OF BACTERIA. 65 



thawing is more injurious than a long exposure 

 to a temperature below o. Spores endure 

 a still lower temperature than the vegetative 

 forms and, indeed, according to Pictet and 

 Young, they may survive for 20 hours at a 

 temperature of -120. According to recent 

 experiments by Pictet, 1 they survive and are 

 able to multiply after being embedded for a 

 short time in frozen oxygen at -213. 



Although, according to Duclaux, the vege- 

 tative cells of some species are able to with- 

 stand a temperature of from 9O-ioo, most 

 species enter into a kind of heat rigor at 42- 

 45 and like other organisms are killed by 

 temperatures of over 55. The spores of the 

 more resistant species are destroyed by boiling 

 water and steam only after 6 hours exposure, 

 and by steam under pressure, at no-i2o, 

 after half an hour. (In contrast to this, the 

 digestive and bacterial enzymes when in the 

 moist condition are destroyed by temperatures 

 of above 70 and of about -i 00. In the dry 

 condition, however, these enzymes withstand 

 the action of high temperatures up to -170.) 

 The dense membrane of the endospores and the 

 relatively small amount of water contained in 

 their protoplasm protects them effectively 

 against temperature oscillations. 



1 Arch, des sci. phys et nat. XXX., 1893, P- 2 93- 



