Having made many experiments with solutions of ammonic tartrate and sodic phosphate, I have almost invariably observed that such solutions--when exposed to the air without having been boiled--become turbid in the course of a few days owing to the presence of myriads of _Bacteria_ and _Vibriones_, with some _Torulæ_. These organisms seem to appear and multiply in such a solution almost as readily as they do in an organic infusion. On the other hand, having frequently boiled such solutions, and closed the flasks during ebullition, I have invariably found, on subsequent examination of these fluids, that whatever else may have been met with, _Bacteria_ and _Vibriones_ were always absent. The difference was most notable, and it seemed only intelligible on the supposition that any living _Bacteria_ or dead ferments which may have pre-existed in the solution, were deprived of their virtues by the preliminary boiling. These experiments also seemed to show that such solutions, after having been boiled, and shut up in hermetically-sealed flasks, from which all air had been expelled, were quite incapable of giving birth to _Bacteria_. The unboiled fluid, exposed to the air, might have become turbid, because it was able to nourish any living _Bacteria_ which it may have contained, or because it was capable of evolving these _de novo_, under the influence of dead ferments whose activity had not been destroyed by heat. Hence we have a fluid which is eminently suitable for testing the vital resistance of _Bacteria_,--one which, although quite capable of nourishing and favouring their reproduction, does not appear capable of evolving them, when, after previous ebullition, it is enclosed in a hermetically sealed flask from which all air has been expelled. Three flasks were half-filled with this solution.[32] The neck of the first (_a_) was allowed to remain open, and no addition was made to the fluid. To the second (_b_), after it had been boiled and had become cool, was added half a minim of a similar saline solution, which had been previously exposed to the air, and which was quite turbid with _Bacteria_, _Vibriones_ and _Torulæ_. From this flask--after its inoculation with the living organisms--the air was exhausted by means of an air-pump, and its neck was hermetically sealed during the ebullition of the fluid, without the flask and its contents having been exposed to a heat of more than 90° F. The third flask (_c_) was similarly inoculated with living _Bacteria_, although its contents were boiled for ten minutes (at 212° F.), and its neck was hermetically sealed during ebullition. The results were as follows:--the solution in the first flask (_a_), became turbid in four or five days; the solution in the second (_b_), became turbid after thirty-six hours; whilst that in the third flask (_c_), remained perfectly clear. This latter flask was opened on the twelfth day, whilst its contents were still clear, and on microscopical