viously been well rinsed with boiling water. A number of glass bottles or tubes were also prepared, which, together with their stoppers or corks, had been boiled in ordinary tap water for a few minutes.* They were taken out full of the boiling fluid; and the stoppers or corks being at once inserted, the vessels and their contents were set aside to cool. When the filtered infusion of hay or turnip had been rapidly cooled down to about 110° F. (by letting the beaker containing it stand in a large basin of cold water), it was inoculated with some of a turbid infusion of hay swarming with active Bacteria and Vibriones-in the proportion of one drop of the turbid fluid to each fluid ounce of the now clear filtered infusion.† The beaker was then placed upon a sand-bath, and its contained fluid (in which a thermomefor was immersed) gradually raised to the required temperature. The fluid was maintained at the same temperature for five minutes by alternately raising the beaker from and replacing it upon the sand-bath. The bottles to be used were then one by one uncorked, emptied,

* The vessels employed have varied in capacity from two drachms to four ounces; some have been provided with glass stoppers and others with very tightly fitting corks; and the latter I find have answered quite as well as the former. On the whole I have found tightly corked oneounce phials to be about the most convenient vessels to employ in these inoculation experiments.

It was found desirable to filter the infusions after they had been boiled, because the boiling generally somewhat impaired their clearness.

and refilled to the brim with the heated inoculated fluid.* The corks or stoppers were at once very tightly pressed down so as to leave no air between them and the surface of the fluids. The beaker was then replaced upon the sand-bath and the gas turned on more fully, in order that the experimental fluid might be rapidly raised to a temperature 9° F. (5° C.) higher than it had been before. After five minutes' exposure to this temperature other bottles were filled in the same manner, and so on for the various temperatures the influence of which it was desired to test.

Thus prepared, the bottles and tubes have been exposed during the day to a temperature ranging from 65° F to 75° F. And generally one had not to wait long in order to ascertain what the results were to be. In some cases, if the contents of the vessels were to become turbid, this was more or less manifest after an interval of forty-eight hours; in other cases, however, the turbidity manifested itself three or more days later: the reason of this difference will be fully discussed in a subsequent communication.

For the sake of simplicity and brevity, the necessary particulars concerning the 102 experiments have been embodied in the following Table :

*

At this stage, of course, very great care is needed in order to avoid all chance of accidental contamination either with living organisms or with unheated fragments or particles of organic matter.

Inoculation Experiments made with the view of ascertaining the Temperatures at which Bacteria, Vibriones, and their supposed Germs are killed in Organic Infusions.

The experimental results above tabulated seem naturally divisible into three groups. Thus, when heated only to 131° F., all the infusions became turbid within two days, just as the inoculated saline solutions had done.* Heated to 158° F. all the inoculated organic infusions remained clear, as had been the case with the saline solutions in my previous experiments when heated to 140° F. There remains, therefore, an intermediate heat zone (ranging from a little below 140° to a little below 158° F.) after an exposure to which the inoculated organic infusions are apt to become more slowly turbid, although inoculated saline solutions raised to the same temperatures invariably remain unaltered. The full explanation of these apparent anomalies I propose to make the subject of a future communication to the Royal Society; meanwhile we may quite safely conclude that Bacteria, Vibriones, and their supposed germs are either actually killed or else completely deprived of their powers of multiplication after a brief exposure to the temperature of 158° F. (70° C).

This evidence now in our possession as to the limits of 'vital resistance' to heat displayed by Bacteria, Vibriones, and their supposed germs in neutral saline solutions, and in neutral or acid organic infusions, is * In the experiments already referred to, p. 85.

most pertinent and valuable when considered in relation to that supplied by other sets of experiments bearing upon the all-important problem of the Origin of Life. These latter experiments alone may possibly leave doubt in many minds; but the more thoroughly they are considered in relation to the evidence brought forward in this communication, the more fully, I venture to think, will every lingering doubt as to the proper conclusion to be arrived at be dispelled.

Thus we now know that boiled turnip or hay-infusions exposed to ordinary air, exposed to filtered air, to calcined air, or shut off altogether from contact with air, are more or less prone to swarm with Bacteria and Vibriones in the course of from two to six days; but, placed under slightly different conditions such as were employed in the inoculation experiments above quoted, although infusions of the same nature do not undergo 'spontaneous' putrefactive changes, yet when living Bacteria and Vibriones are added, and not subsequently heated, putrefaction invariably takes place and the fluids thus situated rapidly become turbid. There is therefore nothing in the conditions themselves tending to hinder the process of putrefaction, so long as living units are there to initiate it. Our experiments now show that as long as the added Bacteria, Vibriones, and their supposed germs are subjected to a heat not exceeding 131°F. (55° C.),