necessary to hill Bacteria,, Vibriones, fyc. 337 



What we have learned, therefore, concerning the invariable uniformity 

 of simple inoculation experiments should of itself teach us how difficult 

 it would be to account for cases of delayed putrefaction, or for cases in 

 which a mere smouldering fermentation is set up, by the old though now 

 well-nigh exploded notion of contamination by preexisting germs. Where 

 living ferments really exist, the course of events is definite and almost in- 

 variable in its rapidity ; but where fermentation takes place as a result of 

 chemical changes occurring in the fluid itself (either by its own unaided 

 powers, or under the stimulating influence of a less-heated organic fer- 

 ment) there is abundant room for all the irregularity and variation actually 

 encountered. These cases of irregularity and variation have always, on 

 other grounds, defied all legitimate attempts to bring them individually 

 within the pale of a narrow and exclusively " vital " theory of fermenta- 

 tion ; and now a wider experience with living ferments equally tends to 

 show the impossibility of legitimately explaining a great mass of irregular 

 phenomena by means of agents whose action is shown to be constant 

 and almost invariable. 



Thus it can now be proved, by evidence of a most unmistakable nature, 

 that the process of putrefaction which invariably occurs in previously 

 boiled putrescible infusions contained in flasks with narrow but open 

 necks is not commonly (is, perhaps, only very rarely) initiated by living 

 germs or organisms derived from the atmosphere ; it can also be proved 

 that putrefaction and the appearance of swarms of living organisms may 

 occur in some boiled fluids when they are simply exposed to air which 

 has been filtered through a firm plug of cotton-wool or through the nar- 

 row and bent neck of a flask, to air whose particles have been destroyed 

 by heat, or even in fluids hermetically sealed in flasks from which all 

 air has been expelled. The evidence in our possession is therefore most 

 complete on this part of the subject : it shows beyond all doubt, not only 

 that putrefaction may and does very frequently occur under conditions in 

 which the advent of atmospheric particles, whether living or dead, is no 

 longer possible, but also that living particles derived from the atmosphere 

 can only be very rare and altogether exceptional initiators of the putre- 

 faction which invariably occurs in previously boiled infusions exposed to 

 the air. 



Again, the evidence which we now possess with reference to the influence 

 of heat upon Bacteria, Yihriones, and their supposed germs is no less deci- 

 sive. It has been unmistakably proved that such organisms and their 

 imaginary germs are either actually or potentially killed by a brief expo- 

 sure to the temperature of 140° F. when in the moist state ; and it had 

 also been previously established that they are invariably killed by desic- 

 cation even at much lower temperatures *. 



* See the experiments and conclusions of Dr. Burdon Sanderson in Thirteenth 

 Report of Med. Officer of Privy Council, p. 61. This fact of the inability of these or- 



