64 BACTERIOLOGY. 



which formed spores even when the water was 

 covered with ice. The majority of soil and 

 water bacteria, however, pass into a kind of 

 cold rigor when the temperature falls to a low 

 point and are no longer able to increase. They 

 grow and multiply only at a temperature above 

 5 C, and thrive best at about 20 C. ; the path- 

 ogenic germs find their optimum at the blood 

 temperature of about 37. Globig, 1 however, 

 discovered species in soil which have adapted 

 themselves to the high temperature of the 

 upper layers of the soil, a temperature which, 

 through direct action of the sun's rays, ranges 

 between 15 and 68 ; he has also observed 

 others which grow only between 54 and 64, at 

 a temperature, that is, at which proteid is usual- 

 ly altered. Van Tieghem observed one species 

 which grows and forms spores even at 74, 

 and refuses to multiply only when 77 is 

 reached. Not even those Cyanophycecz and 

 diatoms which grow upon the deposits in hot 

 springs are able to endure as high a tempera- 

 ture. 



The temperature necessary to produce death 

 varies also extraordinarily. Simple freezing 

 destroys many vegetative cells, but man}^ on 

 the other hand, withstand the shock. Ex- 

 posure to rapid alternation of freezing and 



1 Zeitschr. f. Hyg., III., 1888.- 



