CONDITIOIirS FATOUEING FERMENTATION. 47 



suitable experimental conditions, cause this fluid to ferment 

 and swarm with organisms *, though when it is simply boiled in 

 its acid state it may remain barren. The explanation which ap- 

 plies to one will doubtless apply to the other set of results. We 

 have, in fact, to deal with only one question : — Why does a certain 

 quantity of potash added to an acid infusion endow it with a 

 higher fermentability than it previously possessed ? 



Of the two explanations of this fact which were said to be pos- 

 sible on p. 14, the lirst has been fully disproved, as I have above 

 shown. The second now remains for our consideration, 



2. The I'otash must exercise some Chemical or Physical In- 

 fluence in initiating Fermentative Changes. — In regard to this 

 mode of action two possibilities present themselves, and two 

 only. It must act either {a) by leading to the de novo forma- 

 tion of germs ; or else (h) by reviving germs hitherto presumed to 

 have been killed in boiled acid infusions. 



(«) It is perfectly clear that, if M. Pasteur and others are right 

 in supposing that all ferment-organisms and their germs are killed 

 in boiled acid fluids, no other conclusion is now to be drawn ex- 

 cept that fermentation may he initiated in the absence of living or- 

 ganisms, and that in the course of the process specks of living matter 

 appear de novo as insoluble products of the changing liquid. 



(fi) But if he and others have not been right in supposing that 

 ferment-organisms and their germs are killed in boiled acid liquids, 

 no such conclusion can be drawn from these experiments, and 

 another interpretation would present itself, viz. that the fertilizing 

 agent acts by reviving andfavouring the vital manifestations of germs 

 hitherto presumed to have been hilled in the boiled acidfiuid'\. 



* The greater difEculty and delicacy of the treatment necessary when we seek 

 to induce fermentation by adding the liquor potasste afterwards is doubtless 

 due to the fact that in this case the iiuid has been boiled in its acid state. In 

 this condition, as I have already pointed out (p. 35), the temperature of 

 ebullition is higher ; and therefore the destructive influence of boiling such a 

 fluid would, even on this account alone, be greater than if the alkali had been 

 added beforehand. 



t M. Pasteur's present interpretation of my experiments practically amounts 

 to an adoption of this position (Compt. Eend. July 23, 1877), though apparently 

 he has not yet recognized that, if it proves to be true, it must be equally 

 applicable to his own previous experiments with milk and neutralized yeast- 

 water — in which the alkali was added before boiling. If any germs or chemical 

 ferments can survive on the walls of the experimental vessel, they must be in a 

 state in which they are not actually killed in acid fluids, since in my experi- 

 ments the reversal of half-full flasks or retorts during the two methods of heat- 



