126 THE EVOLUTION OF LIFE 

employed were inoculated with a drop of a fluid in 
which myriads of Bacteria were multiplying rapidly, it 
must be supposed that they were multiplying in their 
accustomed manner, as much by the known method 
of fission as by any unknown and assumed mode of 
reproduction—that is by “germs,” whether visible 
or invisible. 
What has already been said would have con- 
stituted a complete answer to Pasteur at the time 
of the publication of his memoir, and for more than 
ten years later; because at that time the actual 
spores of Bacilli were unknown, and what Pasteur 
spoke of as “germs” of Bacteria and Vibriones 
were mere hypothetical bodies which neither he nor 
any one else had ever seen. At that period 
Bacteria and Vibriones were actually known to 
multiply only by processes of fission. 
Later, in 1875, the glistening and refractive 
spores of Bacilli were discovered, and much has been 
said concerning the powers possessed by these 
bodies of resisting heat, especially after a previous 
thorough desiccation, The extent of their powers 
in this direction has been since most carefully tested 
by me, as I have shown in Chapter x. But, for 
very valid reasons, the nourishing fluid in which 
their powers of resistance were tested had an acid 
reaction, so that the results then arrived at cannot be 
quoted here in reference to the question dealt with 
in this chapter. Seeing, however, that Bacteria and 
Vibriones, which have not undergone a previous 
desiccation, have been shown to be killed (or at least 
