50 FORMATION AND GERMINATION OF SPORES. 



importance, and of this the following examples may be 

 cited : 



1. Some bacteria thrive much better together with others 

 than when alone. Some anaerobes thrive even with the 

 admission of oxygen, if only certain aerobic varieties are 

 present. (Compare B. tetani.) 



2. Certain chemical transformations — for example, the 

 breaking up of nitrite with liberation of free nitrogen — are 

 not accomplished by many bacteria alone, while two 

 varieties jointly may do so. This fact is well worth 

 considering when searching for the cause of certain decom- 

 positions. Always when the isolated varieties , acting singly, 

 operate partially or not at all, the effects of combinations must 

 be investigated. 



3. In a similar manner it is observed that, for example, 

 the single individuals of a series of soil bacteria are not 

 pathogenic, while certain combinations, inoculated into 

 animals, make them sick. 1 (Liermann, C. B. vm, 364.) 

 This experience also demands that especial care be taken 

 in searching for the cause of a new or puzzling disease-pic- 

 ture. Many authors believe that cholera has its origin in 

 two germs, " diblastic theory " (Nageli, Buchner). 



4. Attenuated pathogenic varieties — for example, atten- 

 uated tetanus bacilli — may increase in virulence when cul- 

 tivated together with other bacteria; for example, Bact. 

 vulgare. 



E. The Conditions of Spore-formation 

 and Spore-germination. 



The extent of the formation of endogenous spores appears 

 hitherto to have been very insufficiently understood. Ex- 

 cept in a large group of important varieties of bacilli, re- 

 lated to the B. anthracis and the B. tetani, undoubted 



1 Not quite appropriate here is the experience that the metabolic 

 products of one variety of bacterium, under some circumstances, may 

 enhance the action of another variety; for example, the metabolic prod- 

 ucts of the Bact. vulgare the action of the tetanus bacillus. 



