458 Royal Society : — 



Seeing also that these saline solutions were inoculated with a 

 fluid in which B(Ccteria and Vihrioms were multiplying rapidly, 

 we had a right to infer that they were multiplying iu their 

 accustomed manner, " as much by the knowa method of fission, 

 as by any unknown and assumed method of reproduction." So 

 that, as I at the time said*, " These experiments seem to show, 

 therefore, that even if Bactena do multiply by means of invisible 

 gemmules, as well as by the known process of fission, such in- 

 visible particles possess no higher power of resisting the de- 

 structive influence of heat than the parent Bacteria themselves 

 possess." 



This is, in fact, by far the most satisfactory kind of evidence 

 that can be produced concerning the powers of resisting heat en- 

 joyed by Bacteria and Vihriones, because it also fully meets the 

 hypothesis as to their possible multiplication by invisible gemmules 

 possessed of a greater power of resisting heat, and because no 

 mere inspection by the microscope of dead Bacteria can entitle 

 us positively to afiirm that they are dead, even though all cha- 

 racteristically vital or " true living" .movements may be absent. 



Facts of a very similar nature were mentioned in the same 

 work strongly tending to show that Bacteria and Vihriones are 

 also killed at the same temperature in other fluids, such as infu- 

 sions of hay or turnip. These facts were referred to in the follo\\'ing 

 statementt : — " Thus, if on the same slip, though under different 

 covering-glasses, specimens of a hay-infusion turbid with Bacteria 

 are mounted, («) without being heated, {h) after the fluid has been 

 raised to 122° F. for ten minutes, and (c) after the fluid has been 

 heated to 140° F. for ten minutes, it will be found that in the 

 course of a few days the Bacteria under a and h have notably 

 increased in quantity, whilst those under c do not become more nu- 

 merous, however long the shde is kept. Facts of the same land 

 are observable if a turnip-infusion containing living Bacteria is ex- 

 perimented with ; and the phenomena are in no way different if a 

 solution of ammonic tartrate and sodic phosphate (containing 

 Bacteria) be employed instead of one of these vegetable infusions. 

 The multiplication of the Bacteria beneath the covering-glass, 

 when it occurs, is soon rendered obvious, even to the naked eye, 

 by the increasing cloudiness of the film." 



The facts just cited concerning the behaviour of thin films of 

 turbid infusions which had been heated to different temperatures 

 gave me the clue as to the proper direction of future work. It 

 would seem that, when mounted in the manner described, such 

 thin films of infusion continue capable of supporting and favouring 

 the multiplication of any already existing Bacteria, and Vihriones, 

 although under such conditions no new birth of living particles 

 appears to take place even in these fluids. The question then 

 arose as to whether, by subjecting lai'ger quantities of the same 

 infusions to any particular sets of conditions, we could ensure 



* Modes of Origin of Lowest Organisms, 1871, p. 60. t Loc. cii. p. CO. 



