THE VITAL PHENOMENA OF BACTERIA. 143 



cannot exert its peculiar activity, it generally 

 adapts itself to the new conditions so com- 

 pletely that it entirely unlearns its original 

 mode of action. In our laboratories many 

 disease and ferment germs have become harm- 

 less saprophytes though long-continued culti- 

 vation in nutrient broth or gelatin. It is possi- 

 ble also, if the attempt be not too long delayed, 

 to accustom these bacteria again to their origi- 

 nal mode of activity by supplying their original 

 conditions of life. 



The form of bacteria, as well as their func- 

 tion, changes in response to changed condi- 

 tions of life. The ray-fungus (Actinomyces) 

 develops its characteristic form only in the 

 animal organism. The so-called tubercle bac- 

 illus is not a bacillus at all from the point of 

 view of bacterial classification, but a parasitic 

 growth-form of a pleomorphic mould. It is 

 now well established that there are species of 

 bacteria that pass through only a small cycle 

 of forms, while other species show many forms 

 in the course of their development, a point 

 that has been elucidated chiefly by the inves- 

 tigations of Zopf and Winogradsky. At one 

 time pleomorphism was generally confounded 

 with the variability of individual forms accord- 

 ing to the substratum, an error to which an 

 end was put some years ago by the demonstra- 



