§ VI.] Conditions of vegetation. Temperature. 51 



sitic life in warm-blooded animals have a higher maximum and 

 optimum is probable beforehand, and has been proved by Koch 

 (60) in the case of the Bacillus of tubercle, in which the limits 

 of temperature were found to be from 28° to 42° C, and its 

 optimum 37-38° C. 



The optimum temperature for the formation of spores in 

 endosporous Bacilli, as far as can be ascertained, approaches 

 that of growth. The temperatures for the germination of the 

 endogenetic spores are higher, at least in the case of the op- 

 timum, being 30-34° C, for instance, in Bacillus subtilis, which 

 however also germinates in the temperature of a room which 

 is somewhere about 20° C. B. Anthracis does not germinate, 

 as far as our experience goes, at 20° C. ; the minimum given 

 for this species is 35-37° C, the optimum can scarcely be much 

 higher. Other species, as B. Megaterium, grow and germinate 

 quite well at a temperature of about 20° C. 



Transgression of the limits of temperature of vegetation in 

 the downward direction without destruction to life is possible in 

 the case at least of a large number of Bacteria, and to such an 

 extent that in view of the phenomena which are known to occur 

 we may even say that there are no limits. Frisch (22) found 

 the power of development in the forms which he examined, and 

 in their vegetative cells, unaffected when they were frozen in a 

 fluid at a temperature of — iio°C. and afterwards thawed 

 again. Bacillus Anthracis is one of the forms which behave in 

 this manner; in the case of other species the point remains 

 undecided, but it is probable that in some of them the lower 

 death-temperature is higher than this. 



The upper death-temperature, so far as is at present known, 

 is about the same for the vegetative cells of the majority of 

 forms, as for most other vegetable cells, 50-60° C. Similar 

 figures are true also for the spores of arthrosporous forms, 

 though this point requires further investigation. Exceptional 

 cases will be mentioned further on. On the other hand, the 

 endogenetic spores of the Bacilli are capable of enduring 



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