18/3.] 



necessary to kill Bacteria, Vibriones, fyc. 



231 



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 multiplica- 

 tion after a brief exposure to the temperature of 158° F. (70° 0.). 



This evidence now in our possession as to the limits of "vital 

 resistance 99 to heat displayed by Bacteria, Vibriones, and their supposed 

 germs in neutral saline solutions, and in neutral or acid organic infusions, 

 is 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 communi- 

 cation, 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 " spon- 

 taneous" putrefactive changes, yet when liviug 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), putrefaction invariably 

 occurs within two days ; whilst, on the contrary, whenever they are 

 subjected to a temperature of 158° F. (70° C.) putrefaction does not occur. 

 To what can this difference be due, except to the fact that the previously 

 living organisms, which, when living, always excite putrefaction, have been 

 * In the experiments already referred to. 



