106 MICROBES AND TOXINS 



for example the B. coli in pure culture, the culture is said 

 to be " pure-mixed." The prey may consist of a dead 

 bacterium. 



In the absence of cultures experiment is difficult ; the study 

 of protozoa is still necessarily attached to the study of their 

 forms, and physiological study takes of necessity the second 

 place to morphological. The method par excellence consists 

 in following the life-cycle of protozoa in their natural 

 surroundings or in their hosts. The study of bacteria has 

 been capable of greater advances, thanks to pure cultures in 

 well-defined media which permit of chemical analysis. The 

 application of similar methods to protozoa is infinitely 

 desirable, not only for the sake of medicine, but also to extend 

 our knowledge of the phenomena of life in general. 



