328 APPENDIX. 



that in which my first experiments were made. On its 

 floor were various bundles of old and desiccated hay, from 

 which, when stirred, clouds of fine dust ascended into the 

 atmosphere. This dust proved to be both fruitful and, in 

 the highest degree, resistant. Prior to the introduction of 

 the hay which produced the dust, no difficulty as regards 

 sterilization had ever been experienced ; subsequent to its 

 introduction my difficulties and defeats began. 



I have twice glanced at periods of boiling amounting to 

 two hundred minutes ; for, after long and laborious trials of 

 shorter periods, I advanced to longer ones, subjecting turnip, 

 cucumber, and other infusions to the boiling temperature 

 for intervals varying from five minutes to three hundred 

 and sixty minutes. Up to a certain point these liquids 

 maintained their power of developing life, but beyond this 

 point complete sterility was the result. In the preliminary 

 experiments bearing upon this question the point of steriliza- 

 tion lay between 180 and 240 minutes. Boiled for the 

 former period the infusions continued fruitful ; boiled for 

 the latter period they remained permanently barren. 



In these and numerous other experiments a method was 

 followed which had been substantially employed by Spal- 

 lanzani and Needham, and more recently by Wyman and 

 Roberts, the method having been greatly refined by the 

 philosopher last named. The flasks were partially filled 

 with the infusions, the portions unoccupied by the liquids 

 being taken up with ordinary unfiltered air. Now as 

 regards the death-point of contagia we know that in air it 

 may be much higher than in water, the selfsame tempera- 

 ture being fatal in the latter and sensibly harmless in the 

 former; hence the doubt whether, in my recent experi- 

 ments, the resistance of the contagium did not arise from 

 the fact of its not being surrounded by liquid water. 



I changed the method, and made a long series of ex- 

 periments with filtered air. They were almost as unsuc- 

 cessful as those made with ordinary air. From time to 

 time I succeeded in producing complete sterility by five 

 minutes' boiling ; but these successes were so checked by 



