Philosophy of Ificrobes. 25 



V. Generation, multiplication. 



1. Spontaneity. — Formerly it was supposed that mi- 

 crobes originated by spontaneous generation in putre- 

 factive media; this origin, indeed, was accepted for 

 all beings the mode of reproduction of which was un- 

 known. The progress of the natural sciences first 

 considerably restricted the scope of this theory, which 

 the experiments of Pasteur triumphantly and abso- 

 lutely combatted. Although it can not be denied that 

 at a period in the remote past organized matter must 

 have been formed spontaneously at the expense of 

 mineral matters, it seems well established now that 

 the molecular association which tends to the constitu- 

 tion of protoplasm is no more produced, at least 

 within the conditions of observation accessible to man, 

 except at the expense of a pre-existent being. We 

 therefore have to consider here, from a practical 

 point of view, only the reproduction of germs by mul- 

 tiplication. 



2. Fission. — Microbes multiply principally by fission. 

 The cells of which they are composed become elon- 

 gated, then divided into two by a transverse groove ; 

 the two segments which result from this division may 

 separate and live independently or may remain united 

 so as to form agglomerations of various kinds ; for 

 example : the chains or chaplets of micrococci 

 which adhere end to end ; the zoogloea to which the 

 same micrococci give rise when united in mass by a 

 gelatinous substance, the jointed filaments of the an- 

 thrax bacillus, etc. 



Fission usually takes place in one direction only, 

 3 



