disposal, it will absorb much, and the weight of yeast formed will be still greater.  The ratio between the weight of ferment formed and that of sugar decomposed may pass through all stages within certain very wide limits, the variations depending on the greater or less absorption of free oxygen.  And in this fact, we believe, lies one of the most essential supports of the theory which we advocate.  In denouncing the impossibility, as he considered it, of a ferment living without air or oxygen, and so acting in defiance of that law which governs all living beings, animal or vegetable, Dr. Brefeld ought also to have borne in mind the fact which we have pointed out, that alcoholic yeast is not the only organized ferment which lives in an anaerobian state.  It is really a small matter that one more ferment should be placed in a list of exceptions to the generality of living beings, for whom there is a rigid law in their vital economy which requires for continued life a continuous respiration, a continuous supply of free oxygen.  Why, for instance, has Dr. Brefeld omitted the facts bearing on the life of the vibrios of butyric fermentation?  Doubtless he thought we were equally mistaken in these:  a few actual experiments would have put him right.

These remarks on the criticisms of Dr. Brefeld are also applicable to certain observations of M. Moritz Traube’s, although, as regards the principal object of Dr. Brefeld’s attack, we are indebted to M. Traube for our defence.  This gentleman maintained the exactness of our results before the Chemical Society of Berlin, proving by fresh experiments that yeast is able to live and multiply without the intervention of oxygen.  “My researches,” he said, “confirm in an indisputable manner M. Pasteur’s assertion that the multiplication of yeast can take place in media which contain no trace of free oxygen. ...  M. Brefeld’s assertion to the contrary is erroneous.”  But immediately afterwards M. Traube adds:  “Have we here a confirmation of Pasteur’s theory?  By no means.  The results of my experiments demonstrate on the contrary that this theory has no true foundation.”  What were these results?  Whilst proving that yeast could live without air, M. Traube, as we ourselves did, found that it had great difficulty in living under these conditions; indeed he never succeeded in obtaining more than the first stages of true fermentation.  This was doubtless for the two following reasons:  first, in consequence of the accidental production of secondary and diseased fermentations which frequently prevent the propagation of alcoholic ferment; and, secondly, in consequence of the original exhausted condition of the yeast employed.  As long ago as 1861, we pointed out the slowness and difficulty of the vital action of yeast when deprived of air; and a little way back, in the preceding section, we have called attention to certain fermentations that cannot be completed under such conditions without going into the causes of these peculiarities.