BACTERIA AND THEIR RELATION TO DAIRYING. 7 



not too unfavorable, the spores, on the other hand, may 

 often continue to live for years after the nutritive solution 

 has died out. It must be noted, however, that there are 

 exceptions to the rule in both cases. The spores are far 

 less susceptible to changes in temperature than the bac- 

 teria themselves. While, e. g., sporeless bacteria generally 

 are killed under favorable conditions within about ten 

 minutes, when exposed to a moist heat of 158-176 F. 

 (70-80 C.), the spores of several species survive after hav- 

 ing been exposed even to live steam for hours. The spores 

 of a certain potato bacillus can stand this treatment for 

 almost six hours without succumbing. A large number 

 of spores are not killed except by dry heat at 266-284 F. 

 (130-140 C.). We thus find among the spores of bacteria 

 some of the most tenacious organisms in the vegetable or 

 the animal world. 



Some bacteria (above all a large number of bacilli) are 

 supplied with fine cilia (Fig. 12), and have under favorable 

 external conditions a lively power of locomotion. 



Pathogenic and Non-pathogenic Bacteria. Some bac- 

 teria have become known and feared from their power of 

 producing infectious diseases in the animal body. Owing 

 to this fact, everything known by the name of bacteria 

 has been the object of fear and suspicion to most peo- 

 ple. This is, however, without any foundation. By far 

 the larger number of bacteria are not disease-producing 

 and are not injurious to the animal organism. Some of 

 the harmless majority distinguish themselves by the fact 

 that they call forth fermentation in all kinds of fermenta- 

 ble fluids, while others, as far as known to modern science, 

 are entirely indifferent. 



In these studies and investigations we shall first of all 



