THE BEGINNINGS OF LIFE. 377 



have suggested themselves to M. Pasteur ; but yet we 

 have no mention of them, or any evidence that they had 

 been considered l . He explains the discrepancy between 

 his earlier and his later experiments by reference to a 

 completely different supposition, and, as on other occa- 

 sions, he does not even suggest to the reader that any 

 different explanation is possible from that which he 

 adduces. He at once assumes that the Bacteria and 

 Vibr'tones which were ultimately found in the milk used 

 in these experiments had been derived from ' germs ' of 

 such organisms which either preexisted in, or had ob- 

 tained access to this fluid before it had been heated, 

 and also (contrary to the general rule which had been 

 previously admitted) he assumed that such supposed 

 preexisting germs were capable of resisting the influ- 

 ence of the heat which causes milk to boil. No direct 

 proof of the latter assumption was ever attempted, 

 though M. Pasteur did afterwards endeavour to bring 

 the cases in which organisms were to be met with 

 under a general law : he supposed that the results ob- 

 tained were due to the absence of acidity in the fluids 

 employed. Neutral or slightly alkaline fluids might 

 yield positive results in repeating Schwann's experi- 

 ments, because, as he alleged, the c germs' of Bacteria 

 and Vibriones were not destroyed by the temperature of 

 2i2F in such fluids. 



1 The experiments and reasonings to which I now allude are 

 detailed in pp. 58-66 of M. Pasteur's Memoir (' Ann. de Chim. et de 

 Phys.' 1862). 



