DEVELOPMENT OF THE BACTERIA. 119 



The degree of resistance to extreme tempera- 

 tures is very variable, according to the species. 

 Thus, according to Frisch, a temperature of 45 to 

 50 (113 to 122 Fah.) is sufficient to kill B. termo, 

 whilst 80 (176 Fah.) does not kill the " Bacteri- 

 dies " (Bacillus). 



The permanent spores are especially remarkable 

 by the tolerance which they possess for high tem- 

 peratures. They have been subjected to 100 

 (212 Fah.) (Schwann), 110 (Pasteur) and even 

 130 (Schrader) without losing their power of 

 germinating. 



We must, however, recognize that the results 

 of the experimenters offer the greatest diversity, 

 the result, according to Cohn, of the difficulty of 

 obtaining an equable distribution of the heat in 

 the media, which are generally bad conductors. 



Cohn has arrived at the following conclusions as 

 the result of numerous experiments made upon 

 the Bacillus of hay infusions : 



1. At a temperature of 45 to 50 (113 to 122 

 Fah.) the Bacillus still multiplies rapidly, and 

 forms as usual membranes and spores, while the 

 other schizophytes existing in the infusion of 

 hay are at this temperature incapable of multi- 

 plication. 



2. At a temperature of 50 to 55 (122 to 131 

 Fah.) all reproduction and development of Bacillus 

 ceases. It neither forms pellicles or spores; the 

 filaments are killed, the spores, on the contrary, 

 preserve, for a longer time (for at least seventeen 

 hours) the property of germinating. 



