$ vi.] Conditions of vegetation. Moisture. 5 3 



iooC. 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 noC. 



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 iooC. 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 Termo, 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, limits 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. 



