154 THE FLOATING-MATTER OF THE AIR. 



two only of the back tubes gave way, the third back 

 tube and the three front tubes remaining clear. 



On the 3rd of November, moreover, a new chamber of 

 six tubes was charged with an infusion of new London 

 hay. Three of the tubes were neutralized and three 

 unneutralized. Both infusions were introduced into the 

 chamber unboiled, and were boiled afterwards for five 

 minutes. In a week all the tubes had given way, be- 

 coming turbid in the same degree and covered to the 

 same extent with scum. The newness of the hay had 

 failed to secure the sterility of the infusions. 



Nothing of this kind occurred in the experiments of 

 last year. It was then found that hay-infusions of all 

 kinds were uniformly sterilized by five minutes' boiling. 



Gruidai by such hints as the experiments furnished, 

 I continued to work. On the 4th of November four 

 closed chambers of three tubes each were charged 

 with infusions of old and new Heathfield hay — two 

 chambers with the one, and two chambers with the 

 other. One chamber of each pair contained a neutral- 

 ized, the other an unneutralized infusion, and the time 

 of boiling was ten minutes. Six days subsequently the 

 infusion of new hay, both neutralized and unneutralized, 

 was found perfectly unchanged. Of the old-hay in- 

 fusion, on the other hand, only one of the six tubes 

 escaped. The three acid tubes became completely tur- 

 bid, while two out of the thi'ee neutral ones fell into the 

 same condition. 



§ 8. Experiments with Soaked Hay. 



Pondering still further on the influence of drying 

 and hardening, and recognizing the necessity of not 

 only wetting but also softening the germs, the thought 



