ON THE NATURE OF FERMENTATION. 179 



Pasteur for the very purpose of affording nourishment to the 

 yeast-plant and other minute organisms. This was prepared on 

 August 7th in a flask purified by heat, covered over with a cap of 

 pure cotton wool/ which permits the entrance of air, but does not 

 permit the access either of the yeast-plant or of any other form of 

 dust. The Pasteur's solution, containing, besides sugar, ammo- 

 niacal and earthy salts for the nutrition of the fungus, was heated 

 to about the temperature of boiling water, so as to destroy any 

 organisms that might exist in the water. The result is, that it 

 continues perfectly unchanged, just as it was on August 7th; 

 but, if we were to add to it a little of the yeast-plant from fer- 

 menting grape-juice, we should find that, at the temperature of 

 summer weather, it would very soon be in a state of free fermen- 

 tation at the same time that the yeast-plant would multiply. 

 This, then, is a typical instance of fermentation. We have an 

 active agent termed the ferment, which ferment is capable of 

 self-multiplication. That I believe to be the essential property 

 of a true fermentation. Now, in this particular case, I have 

 already said it is admitted on all hands that the yeast-plant is 

 the cause of fermentation. Persons may differ as to how the 

 development of the yeast-plant gives rise to the resolution of the 

 sugar into the alcohol and carbonic acid gas ; but all now agree , 

 that, somehow or other, the organism causes the fermentation. 

 Now, is it the case that all true fermentations are caused by the 

 development of organisms ? That, gentlemen, is the question 

 which it is desirable that we should be able to answer. 



Take, for example, the case of the putrefactive fermentation of 

 blood. We all know that, if blood be shed from the body into 

 any vessel without special precautions, in a few days it putrefies. 

 The bland nutrient liquid, soon after leaving its natural recep- 

 tacle, becomes foul, acrid, and poisonous; a change fully as 

 striking as that which grape-juice undergoes in the alcoholic 

 fermentation. Here, on the other hand, we have a vessel (a 

 liqueur-glass) into which blood was received with special pre- 

 cautions. In the first place, the glass, covered, as you see, with 

 a glass cap and a glass shade, with a view of preventing the 

 access of dust, and standing upon a piece of plate-glass, had 

 been heated to about the temperature of 300° Fahr., and cooled 

 with an arrangement which ensured that the air which entered 

 during cooling was filtered of its dust ; so that we were per- 

 fectly sure that the glass contained at the outset no living 

 organisms. 



' The cotton -wool was rendered free from living organisms by soaking 

 it with a solution of carbolic acid iu one hundred parts of anhydrous ether 

 and allowing the ether to evaporate, leaving tiie carbolic acid behind in the 

 cotton. 



