ON THE NATURE OF FERMENTATION. 181 



tendency to putrefaction. It further proves that the oxygen of 

 the air is not able to cause the blood to putrefy, as used to be 

 supposed. There was a time — the effect is still seen to a certain 

 extent — when the dark venous colour of this blood-clot gave 

 place to the crimson colour of arterial blood in a gradually 

 deepening band from above downwards. We still see some of 

 the red colour remaining, though now the converse effect has 

 begun to take place. That florid redness, gentlemen, showed 

 that the oxygen of the air was in reality acting upon the blood, 

 yet it did not putrefy. Now, if I were to take a little morsel of 

 already putrefied blood, say, upon the end of a needle, and touch 

 with it this clot of blood, putrefaction would, in the course of a 

 very short time, spread throughout the mass. Exactly as in the 

 case of alcohoHc fermentation under the influence of the yeast- 

 plant would the fermentation spread. 



Putrefaction, then, is a fermentation, a true fermentation, 

 characterised by the power of self-multiplication of the ferment. 

 Then, gentlemen, if we examine microscopically, we find in the 

 putrefying blood, as we found in the fermenting grape-juice, 

 microscopic organisms, termed bacteria from their rod-shape, 

 which we have represented in this diagram on the same scale as 

 we had the yeast-plant ; of different sizes, but all very much more 

 minute than the yeast-plant, and commonly endowed with a 

 remarkable power of locomotion. I say that, in the putrefying 

 blood, we find these organisms developing pari passu with the 

 fermentation. 



Now, the question is. Are these bacteria the cause of the 

 putrefactive fermentation, or are they merely accidental concomi- 

 tants? These are two views which are entertained at the present 

 day by men of high eminence. It may be said, " Wiiy should 

 there be any doubt that the bacteria are.the cause of the putre- 

 factive fermentation, any more than there is a doubt that the Torula 

 cerevisia is the cause of the alcoholic ?" Well, one reason I believe 

 to be that the bacteria are so exceedingly small. They are not so 

 easily defined as the yeast-plant. We cannot get them in a mass 

 as we can get a mass of yeast ; at least without a great deal of 

 trouble ; and, besides that, they occur very similar in appearance 

 in a great number of different fermentations. There is, there- 

 fore, so far some colour for doubting whether bacteria are the 

 cause of a special fermentation, like this putrefaction. Then 

 there is another ground justifying such a view; for certain it is 

 that organic substances are liable to extremely remarkable altera- 

 tions, decompositions, under the influence of agents which are 

 endowed with no life at all. As good an example of this as we 

 can take is what occurs in the bitter almond when it is bruised 

 with water. You all know what takes place under those circum^ 



