86 MICRO-ORGANISMS AND FERMENTATION. 



Many bacteria are very resistant to low temperatures. 

 J. Forster, B. Fischer, Miquel, and others have shown that 

 bacteria exist which multiply rapidly at the freezing point. 

 Certain species are not killed by exposure to a temperature of 



- 70 C., 110 C., or even to the extreme temperatures of 



- 213 C. and - 252 C. (Frisch, Pictet and Young, Macfadyen, 

 and Rowland). In contrast to these, a number of thermophilous 

 bacteria have been discovered. Miquel has described Bacillus 

 thermophilus, which multiplies readily at 70 C., whilst its 

 development is arrested at 42 C. Other species will only 

 germinate above 60 C. In the excrement of animals many 

 species of frequent occurrence continue to grow at 25 C., 

 whilst their growth is inhibited at about 39 C. (L. Bahino- 

 witsch). The lactic-acid bacteria and certain organisms 

 occurring in molasses, in the fermentation of tobacco, and in 

 the spontaneous heating of hay, belong to the thermophilous 

 species. The bacteria occurring in hay have been examined 

 in detail by Miehe. F. Cohn has also proved that the cause 

 of the spontaneous heating of moist cotton waste is the presence 

 of a micrococcus belonging to this group. It has already been 

 stated that spores will stand a considerably higher temperature 

 than vegetative cells. It is, therefore, obvious that only high 

 temperatures can be used for disinfection. 



With regard to the germicidal action of light, Downes and 

 Blunt found, as early as 1877-1878, that direct sunshine 

 powerfully restricts their growth, and that the most active 

 rays of light are the strongly refractive blue and violet rays, 

 well known to possess powerful photo-chemical properties. 

 On the other hand, red and orange rays are less active, and 

 heat rays which accompany the light rays possess no activity. 



H. Buchner and S. Bang, amongst recent workers, have 

 studied the action of light upon bacteria. Buchner records 

 that sunlight plays a part in the spontaneous purification of 

 rivers by bacteria. It is assumed that the effect of direct 

 sunlight on bacteria is not entirely due to the action on the 

 cells, but also to the alteration brought about in the sub- 

 stratum, whereby it becomes less suited for nutrition. For 

 example, the formation of hydrogen peroxide in nutritive agar 

 by exposure to sunlight has been demonstrated. A few quite 



