Such experiments would seem to be most important and crucial in their nature. They may be considered to settle the question as to the vital resistance of these particular _Bacteria_, whilst other evidence points conclusively in the direction that all _Bacteria_, whencesoever they have been derived, possess essentially similar vital endowments[42]. Seeing also that the solutions have been inoculated with a drop of a fluid in which _Bacteria_, _Vibriones_, and _Torulæ_ are multiplying rapidly, we must suppose that they are multiplying in their accustomed manner, as much by the known method of fission, as by any unknown and assumed method of reproduction. In such a fluid, at all events, there would be all the kinds of reproductive elements common to _Bacteria_, whether visible or invisible, and these would have been alike subjected to the influence of the same temperature. These experiments seem to show, therefore, that even if _Bacteria_ do multiply by means of invisible gemmules as well as by the known process of fission, such invisible particles possess no higher power of resisting the destructive influence of heat than the parent _Bacteria_ themselves possess. This result is, moreover, as I venture to think, in accordance with what might have been anticipated _à priori_. _Bacteria_ seem to be composed of homogeneous living matter, and any gemmule, however minute, could only be a portion of such living matter, endowed with similar properties. [42] The _Bacteria_ and _Vibriones_ with which Professor Wyman experimented were derived from different sources; and so far as I also have been able to ascertain, the _Bacteria_ of different fluids are similarly affected by exposure to similar degrees of heat. Thus, if on the same slip, though under different covering glasses, specimens of a hay infusion, turbid with _Bacteria_, are mounted, (_a_) without being heated, (_b_) after the fluid has been raised to 122° F. for ten minutes, and (_c_) after the fluid has been heated to 140° F. for ten minutes, it will be found that, in the course of a few days, the _Bacteria_ under _a_ and _b_ have notably increased in quantity, whilst those under _c_ do not become more numerous, however long the slide is kept. Facts of the same kind are observable if a turnip infusion, containing living _Bacteria_, is experimented with; and the phenomena are in no way different if a solution of ammonic tartrate and sodic phosphate (containing _Bacteria_) be employed instead of one of these vegetable infusions. The multiplication of the _Bacteria_ beneath the covering-glass, when it occurs, is soon rendered obvious, even to the naked eye, by the increasing cloudiness of the film. _Extent to which boiled Fermentable Fluids may be preserved in Vessels with Bent Necks, or in those whose Necks are guarded by a Plug of Cotton-Wool._