ON THE NATURE OF FERMENTATION. 193 



shown that, if a saccharine solution be put in a very thin layer 

 in an open vessel with yeast, the yeast-plant developes 

 very rapidly, but very little fermentation occurs ; on the 

 contrary, if it be put into a deep vessel, the development of 

 the yeast-plant does not go on so rapidly, but more fermentation 

 results. He explains the fact in this way : that the yeast-plant 

 requires oxygen for its nutrition ; if it get it easily, as it does in 

 a shallow vessel in the air, it produces comparatively little effect 

 in breaking up the sugar into its constituents, and vice versa. So 

 here, in the test-tubes the carbonic acid accumulated, supposing 

 any to exist, as in a well, and the Bacteriiim lactis had but little 

 opportunity for getting oxygen. Accordingly here, just as in 

 M. Pasteur's experiments with a sugary solution with yeast in a 

 deep vessel, the Bacterium lactis produced more rapidly its fer- 

 mentative effect. 



But this, you say, is assuming that Bacterium lactis is the 

 ferment. Now we are coming to that point. But first I have 

 to mention an additional fact. For the satisfaction of others 

 rather than for my own, I went through the laborious process of 

 investigating portions of the contents of all these vessels ; and 

 I found that, in every one in which the lactic acid fermentation 

 had taken place, where there was curdlmg and souring, the 

 Bacterium lactis was present ; and in no instance in which there 

 was no lactic fermentation was any bacterium of any sort to be 

 discovered. I believe that fact demonstrates that the Bacterium 

 lactis is the cause of this very special lactic fermentation. Let 

 us assume for a moment that there did exist some other material 

 besides the Bacterium lactis in the milk capable of causing the 

 fermentation ; that the lactic ferment was not the bacterium at 

 all, but some chemical ferment. First of all, you will please to 

 observe that we have from this experiment absolute evidence 

 that the ferment, of whatever nature, is not in solution, but in 

 the form of suspended insoluble particles. If the ferment had 

 been in solution, every equal sized drop of the water of inocula- 

 tion would have produced the same effect. The fact that some 

 drops were destitute of the ferment proves that that ferment 

 was not in a state of solution. That is absolutely demonstrated. 

 Now, suppose we admit, for the sake of argument, that the lactic 

 acid ferment consisted of particles of some non-living substance, 

 capable of self-multiplication as rapidly as the bacterium, but 

 not living; a strange hypothesis, no doubt — but suppose we 

 assume it. Suppose we admit that the true lactic ferment and 

 the Bacterium lactis were merely accidental concomitants of 

 each other, it would be absolutely inconceivable that these two 

 accidentally associated things should be present in exactly the 

 same numbers. And yet, according to the hypothesis, such 

 would be only another mode of stating our observed fact, which 



