PERSISTENCE OF PUTREFACTIVE AND INFECTIVE ORGANISMS. 
161 
throughout and covered with scum. The scum and turbidity were sensibly the same 
in all the tubes, though the period of boiling varied from five to twenty minutes. On 
the same day the neutralized infusion of the same hay was perfectly brilliant and free 
from scum. Three days subsequently, however (that is to say, on the 10th of November), 
the neutralized tubes also became turbid and covered with scum. 
The salient fact here to be noted is, that in neither the neutral nor the acid chamber 
did a single tube of the old Heathfield hay-infusion maintain its primitive clearness and 
freedom from scum. 
The old London hay behaved substantially as the old Heathfield hay, no single 
tube escaping either in the neutralized or the unneutralized chamber. 
The dried new London hay comes next. A week after its introduction every one of the 
six tubes containing the acid infusion was turbid and coated with scum. In the neu- 
tralized chamber, on the contrary, 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 un- 
neutralized. Both infusions were introduced into the chamber unboiled, and were 
boiled afterwards for five minutes. In a week all the tubes had given way, becoming 
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. 
Guided 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 neutralized, the other an unneu- 
tralized infusion, and the time of boiling was ten minutes. Six days subsequently the 
infusion of new hay, both neutralized and unneutralized, was found perfectly un- 
changed. Of the old-hay infusion, on the other hand, only one of the six tubes 
escaped. The three acid tubes became completely turbid, while two out of the three 
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 occurred to me 
of soaking the hay for some days prior to digesting it. Old London hay was accord- 
ingly chopped up and placed in three glass vessels — one containing distilled water, 
another acidulated water, and a third alkalized water. The superior extractive power 
of the alkalized liquid was at once manifest; it rapidly assumed a dark colour. The 
distilled water came next, yielding a colour less deep than that of the alkalized, but 
