CHAPTER X. 



PHYSICAL AND VITAL THEORIES OF FERMENTATION. 



Questions as to Cause of Fermentation and Origin of Life intimately 

 associated. Pasteur's researches undertaken to establish a ' vital 

 theory ' of Fermentation. Fermentable substances and Ferments. 

 Nature of latter. Doctrine of Liebig and others. Influence of the 

 discovery of the yeast-plant. Vital theories of Schwann, Pasteur, 

 and others. Upholders of Physical theory admit the facts of the 

 Vitalists. Interpretations of latter too narrow. Pasteur's experi- 

 ments inconclusive in themselves. His conclusions wider than 

 were legitimate. Vital theory opposed to known facts. Manu- 

 facture of Vinegar. Continuous series of chemical changes in dead 

 muscle. Transformation of starch into glucose. Communicability 

 of molecular movements No line of demarcation between fer- 

 mentative and non-fermentative chemical changes. Two degrees of 

 fermentability. Oxygen not always the primttm movens in Fermen- 

 tations. Action of diminished pressure in some cases. Preserva- 

 tion of Meats. Differences between these processes and my 

 experiments. Observations of Gruithuisen. Reconciliation of 

 results. Conclusions. 



THE lower organisms being so very frequently met 

 with in fermenting fluids, and being Invariably 

 present in some of them, it so happens that the problem 

 as to the cause of fermentation has come to be in- 

 separable from the question as to the possibility of the 

 de novo origin of living things. Thus it is that the 

 most important problem in biology is one towards the 



