VITALITY OF PUTEEFACTIVE ORGANISMS. 225 



amounts of aerial interspace free from the floating con- 

 tagium. 



§ 25. Critical Review of the last two Sections, 



It has been my desire and aim throughout this 

 inquiry to free it as much as possible from uncer- 

 tainty and doubt. I have tried to render the facts 

 safe by laborious repetition, and the interpretations 

 of those facts secure by close and constant criticism. 

 Thus, in reference to our present subject, I had to put 

 to myself very definitely the question whether the per- 

 manent clearness of an infusion exposed to a very 

 moderate amount of heat, after having been freed from 

 air by boiling or by the Sprengel pump, was really due 

 to the destruction of the germs in the infusion. Even 

 in a highly infective atmosphere, from three to five 

 minutes' boiling in an oil-bath suffices to sterilize our 

 retort-flasks, while it is perfectly certain that exposm-e 

 to the boiling temperature for fifty times this interval 

 may fail to kill the germs of an infusion containing 

 a good supply of atmospheric air. A similar remark 

 applies to our experiments with the Sprengel pump. 

 I asked myself whether in these cases the life of the 

 germs was not suspended merely, instead of being 

 destroyed. It was quite conceivable that germs en- 

 dowed with vital power, ready to act under proper 

 conditions, might still exist in our hermetically-sealed 

 flasks, although the entire absence of oxygen rendered 

 their further development impossible. 



That something more than a mere temporary hind- 

 rance to development is here involved was, however, 

 proved by many of the experiments just recorded. 

 These experiments showed that after hermetically-sealed 

 flasks had remained pellucid, not only for days but for 



