98 



MICRO-ORGANISMS AND FERMENTATION. 



that often very considerably. Thus an endless variety of 

 polymorphous swollen forms are produced (Fig. 21). It is not 

 till then that the threads are divided into small links, giving 

 rise to typical chains. Only the thickest parts of the swollen 

 threads remain undivided, and are at last dissolved. Thus the 



Fig. 20. Bacterium Pewtewriant/iw. The thread form after cultivation for 24 hours on 

 "double beer" at 40-40'5 C. (after Hausen). 



swollen forms play a regular part in the cycle of changes. 

 This cycle furnishes a striking example of the effect of tem- 

 perature in determining the form assumed by bacteria. 



The species Bacterium aceti and Bacterium Pasteurianum 

 differ, according to Lafar, both chemically and chemico- 



