[Illustration:  Figure 14.]

On June 28th, fermentation was quite finished; there was no longer any trace of gas, nor any lactate in solution.  All the infusoria were lying motionless at the bottom of the flask.  The liquid clarified by degrees, and in the course of a few days became quite bright.  Here we may inquire, were these motionless infusoria, which from complete exhaustion of the lactate, the source of the carbonaceous part of their food, were now lying inert at the bottom of the fermenting vessel—­were they dead beyond the power of revival? [Footnote:  The carbonaceous supply, as we remarked, had failed them, and to this failure the absence of vital action, nutrition, and multiplication was attributable.  The liquid, however, contained butyrate of lime, a salt possessing properties similar to those of the lactate.  Why could not this salt equally well support the life of the vibrios?  The explanation of the difficulty seems to us to lie simply in the fact that lactic acid produces heat by its decomposition, whilst butyric acid does not, and the vibrios seem to require heat during the chemical process of their nutrition.] The following experiment leads us to believe that they were not perfectly lifeless, and that they might behave in the same manner as the yeast of beer, which, after it has decomposed all the sugar in a fermentable liquid, is ready to revive and multiply in a fresh saccharine medium.  On April 22nd, 1875, we left in the oven at a temperature of 25 degrees C. (77 degrees F.) a fermentation of lactate of lime that had been completed.  The delivery tube of the flask A, (Fig. 15), in which it had taken place, had never been withdrawn from under the mercury.  We kept the liquid under observation daily, and saw it gradually become brighter; this went on for fifteen days.  We then filled a similar flask, B, with the solution of lactate, which we boiled, not only to kill the germs of vibrios which the liquid might contain, but also to expel the air that it held in solution.  When the flask, B, had cooled, we connected the two flasks, avoiding the introduction of air, [Footnote:  To do this it is sufficient, first, to fill the curved ends of the stop-cocked tubes of the flasks, as well as the india-rubber tube C C which connects them, with boiling water that contains no air.] after having slightly shaken the flask, A, to stir up the deposit at the bottom.  There was then a pressure due to carbonic acid at the end of the delivery tube of this latter flask, at the point A, so that on opening the taps R and S, the deposit at the bottom of flask A was driven over into flask B, which in consequence was impregnated with the deposit of a fermentation that had been completed fifteen days before.  Two days after impregnation the flask B began to show signs of fermentation.  It follows that the deposit of vibrios of a completed butyric fermentation may be kept, at least for a certain time, without losing the power of causing fementation.  It furnishes a butyric ferment, capable of revival and action in a suitable fresh fermentable medium.