140 THE ROYAL SOCIETY OF CANADA 



mospheric pressure. Bullock, it is true, has one interesting incidenta - 

 observation which may throw some light upon my results: he notes 

 that B. suhtilis spores are more easily killed in bouillon than in normal 

 saline solution. Now my observations were made with bouillon. 

 One out of five coverslips smeared with the spores still grew after 

 immersion in normal saline solution in the autoclave for 45 minutes 

 at 101.5 °C. : nineteen coverslips smeared with the same and immersed 

 in bouillon were all rendered sterile at this temperature in 30 minutes. 

 An interesting point, to which Bullock does not call attention, is that 

 his method and his tables clearly demonstrate the existence in his 

 culture of spores having varying resistances to high temperatures. 

 Dr. Malone and I take up this matter in an article shortly to be pub- 

 lished. 



IV. Lastly, I am inclined to think the observations just recorded 

 answer Principal Harrison's final criticism. We have to recognize 

 that the resistance of spores to heat varies greatly according to their 

 environment. In media like glycerine which favor exosmosis the re- 

 sistance is raised, in those favouring endosmosis the resistance is lowered. 

 My observations should not be taken as evidence that all spores are 

 easily destroyed by heat. 



May I be permitted here again to acknowledge my indebtedness 

 to Professor Adami for his kind supervision. 



