SPONTANEOUS GENERATION. 315 



place : ' It has been shown that the briefest exposure 

 to the influence of boiling water is destructive of all 

 living matter.' ' 



The experiments already recorded plainly show that 

 there is a marked difference between the dry bacterial 

 matter of the air, and the wet, soft, and active bacteria 

 of putrefying organic liquids. The one can be luxu- 

 riantly bred in the saline solution, the others refuse to 

 be born there, while both of them are copiously de- 

 veloped in a sterilized turnip infusion. Inferences, as 

 we have already seen, founded on the deportment of 

 the one liquid cannot with the warrant of scientific 

 logic be extended to the other. But this is exactly what 

 the heterogenist has done, thus repeating as regards 

 the death-point of bacteria the error into which he 

 fell concerning the germs of the air. Let us boil our 

 muddy mineral solution with its swarming bacteria for 

 five minutes. In the soft succulent condition in which 

 they exist in the solution not one of them escapes 

 destruction. The same is true of the turnip infusion 

 if it be inoculated with the living bacteria only — the 

 aerial dust being carefully excluded. In both cases the 

 dead organisms sink to the bottom of the liquid, and 

 without re-inoculation no fresh organisms will arise. 

 But the case is entirely different when we inoculate 

 our turnip infusion with the desiccated germinal matter 

 afloat in the air. 



The 'death-point' of bacteria is the maximum 

 temperature at which they can live, or the minimum 

 temperature at which they cease to live. If, for ex- 

 ample, they survive a temperature of 140°, and do not 

 survive a temperature of 150°, the death-point lies 

 somewhere between these two temperatures. Vaccine 

 lymph, for example, is proved by Messrs. Braidwood 

 and Vacher to be deprived of its power of infection by 

 ' Bastian, ' Evolution,' p. 46. 



