viii PREFACE. 



M. Pasteur had fallen, and also how his con- 

 clusions were capable of being reversed by the 

 employment of different experimental materials, 

 and different experimental methods. Then, having 

 presented, in a connected form, evidence which 

 might suffice to shake the faith of all who 

 preserved a right of independent judgment, one 

 might hope to have paved the way for the recep- 

 tion of new views even though they were adverse 

 to those of M. Pasteur. The present volume con- 

 tains, indeed, only a fragment of the evidence 

 which will be embodied in a much larger work 

 now almost completed relating to the nature 

 and origin of living matter, and in favour of 

 what is termed the physical doctrine of Life. 



The question of the mode of origin of Living 

 Matter, is inextricably mixed up with another pro- 

 blem as to the cause of fermentation and putrefaction. 

 M. Pasteur's labours were, at first, undertaken in 

 order to solve the latter difficulty to decide, 

 in fact, between two rival hypotheses. It was 

 held, on the one hand, that many ferments 

 were mere dead nitrogenous substances, and that 

 fermentation was a purely chemical process, for 

 the initiation of which the action of living organ- 

 isms was not necessary ; whilst, on the other hand, 



