272 MICROBES, FEUMENTS, AND MOULDS. 



CHAPTER VIIL 



POLYMORPHISM OF MICROBES. 



MICROBES (bacteria, ferments, and moulds) display, 

 like all the lower types of the animal and vegetable 

 kingdoms, considerable polymorphism. It is necessary, 

 therefore, that we should be on our guard, lest this 

 phenomenon should be the source of errors and con- 

 fusions very prejudicial to science, either by describing 

 as distinct species different forms of the same species, 

 or by being, on the other hand, led to regard as one 

 and the same species several which are really distinct, 

 and which for want of proper precautions, have been 

 brought together in the same preparation, without the 

 observer being aware of the fact. 



We have indicated in the foregoing chapter the 

 scrupulous care which is indispensable in laboratories 

 in order to guard against surprises of this kind. 

 These precautions are not always sufficient, and ex- 

 perience shows that a single act of forgetfulness or 

 distraction on the part of the observer is enough to 

 spoil the result of a long series of researches. More- 



