272 MICROBES, FERMEN'TS, AND MOULDS, 
CHAPTER VIII 
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- 
