On the Heat necessary to kill Bacteria &c. 457 



Nearly two years ago, in my ' Modes of Origiu of Lowest 

 Organisms,' I brought forward evidence to show that Bacteria, 

 Vibriones, and their supposed germs are killed at a temperature of 

 140° F. (60° C.) in neutral or very faintly acid solutions containing 

 ammonic tartrate and sodic phosphate, and also evidence tending 

 to show that these Kviug units were killed in neutral infusions 

 of hay and in acid infusions of turnip at the same temperature. 



The crucial evidence adduced concerning the degree of heat 

 destructive to Bacteria, Vibriones, and their germs, in the saUne 

 solution, was of this nature. The solution had been shown to be 

 incapable of engendering Bacteria and Vibriones (under all ordi- 

 nary conditions) after it had been boiled, although it still continued 

 capable of supporting the life and encouraging the rapid multi- 

 plication of any of these organisms which -were purposely added to 

 it. Some of this boiled solution, therefore, was introduced into 

 flasks previously washed with boiling water ; and when the fluids 

 had suflficiently cooled, that of each flask was inoculated A^ith 

 living Bacteria and Vibriones — in the proportion of one drop of 

 a fluid quite turbid with these organisms to one fluid ounce of the 

 clear saline solution*. These mixtures containing an abundance 

 of living organisms were then heated to various temperatures, 

 ranging from 122° P. (50° C.) to lG7°r. (75° C); and it was in- 

 variably found that those which had been heated to 122° or 131° P. 

 became quite turbid in about two days, whilst those which had 

 been raised to 140° P. or upwards as invariably remained clear 

 and unaltered. The turbidity in the first series having been ascer- 

 tained to be due to the enormous multiplication of Bacteria and 

 Vibriones, and it being a well-established fact that such organisms 

 when undoubtedly living always rapidly multiply in these fluids, 

 the conclusion seemed almost inevitable that the organisms and 

 their germs must have been killed ia the flasks which were briefly 

 subjected to the temperature of 140° P. How else are we to 

 account for the fact that these fluids remained quite unaltered 

 although"' li\ing organisms were added to them in the same pro- 

 portion as they had been to those less-heated fluids which had 

 so rapidly become turbid ? Even if there does remain the mere 

 possibility that the organisms and their supposed germs had not 

 actually been killed, they were certainly so far damaged as to 

 be unable to manifest any vital characteristics. The heat had, at 

 all events, deprived them of their powers of growth and multipli- 

 cation ; and these gone, so little of what we are accustomed to call 

 " life " could remain, that practically they might well be con- 

 sidered dead. And, as I shall subsequently show, the production 

 of this potential death by the temperature of 1 40° P. enables us to 

 draw just the same conclusions from other experiments, as if 

 such a temperature had produced a demonstrably actual deathf. 



* Fuller details concerning these experiments may be found in the little 

 work already mentioned at pp. 51-56, and also in ' The Beginnings of Life, ' 

 vol. i. pp. 325-332. 



t See p. 462. 



