^ VI.] Conditions of vegetation. Moisture. 53 



ioo°C. capable of germination; if they remained in it at the 

 same temperature for half an hour the majority still germinated, 

 if for one hour a smaller number; none retained their vital 

 power after a space of three hours. The spores were killed in 

 fifteen minutes at a temperature of 105° C, in ten minutes at 

 107° C, in five minutes at iio°C. 



Fitz (21) found that the spores of his Bacillus butylicus 

 (B. Amylobacter) bear a temperature of 100° C.for a time vary- 

 ing from three to twenty minutes, according to the fluid in 

 which they happen to be. But if the time of exposure is pro- 

 longed, temperatures under 100° C. are sufficient to kill them, 

 80° C. for example, when they are kept seven to eleven hours 

 in glycerine solution. 



Spores, at least, are proof against still higher degrees of dry 

 heat ; those of Bacillus Anthracis, B. subtilis, and others con- 

 tinued capable of development in Koch's experiments (14, p. 305) 

 in a chamber heated up to 123° C. 



Among the conditions connected with the nature of the en- 

 vironment, the requisite supply of water must be mentioned first 

 in this case as in that of all living cells. Withdrawal of water 

 to the point of air-dryness not only stops the process of vege- 

 tation but kills vegetative cells, at least in a number of cases, 

 in a very short time, those of Bacterium Terroo, Cohn, and B. 

 Zopfii, for example, in seven days. But here, too, the effect 

 varies in different cases ; Micrococcus prodigiosus, for instance, 

 continues alive and capable of development for months in a 

 state of desiccation. 



The resistance of spores to desiccation is greater than that of 

 vegetative cells. The spores of the arthrosporous Bacterium 

 Zopfii withstand it for seventeen to twenty-six days; those of 

 the endosporous Bacilli on the average certainly a year, those of 

 Bacillus subtilis, according to Brefeld, at least three years. 

 Here, too, hmits and modifications will arise according to other 

 internal and external causes, but air-dry cells can hardly be 

 expected to retain their vitality for centuries. 



