PEESISTENCE OE PUTEEEACTIYE AND INEECTIYE OEGANISMS. 
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§ 5. Hay-infusions (in Closed Chambers). 
In dealing with hay-infusions I also fell back on the method of experiment which 
was found so effectual last year*, employing closed chambers in which the air had 
been permitted to cleanse itself by the gradual subsidence of its floating matter. 
On the 3rd of October, 1876, my experiments with such chambers recommenced. 
Two of them, containing each three large test-tubes, were then charged with an infusion 
of hay accurately prepared according to the prescription of Dr. Roberts. Its specific 
gravity was 1006 ; it was superneutralized to the proper extent with caustic potash, but 
the period of boiling, instead of being three hours, was five minutes. 
Examined from time to time for more than four months subsequently, the infusion 
in both chambers continued perfectly unchanged. It was free from suspended matter, 
free also from every trace of scum, maintaining for the light which passed through it a 
singular transparency. 
Here, to a certainty, a period of boiling not amounting to one twentieth of that 
required by Dr. Roberts sufficed to destroy totally the power of generating life in an 
alkalized hay-infusion. 
This result is in perfect harmony with all the results of last year. Chamber after 
chamber was then charged with infusions of hay, which were afterwards subjected to 
the boiling temperature for five minutes. In every chamber the infusion remained 
perfectly clear until purposely infected from without. There was no instance observed 
last year in which five minutes’ boiling failed to sterilize hay-infusion, whether neutralized 
or unneutralized. 
Thus, on the 26th of November, 1875, a group of three test-tubes was charged with 
hay-infusion of the same specific gravity and of the same degree of alkalinity as that 
found most resistant by Dr. Roberts. They were protected by glass shades, the air 
within the shade being calcined by an incandescent platinum wire in the manner 
described in my last paperf. The tubes were boiled for five minutes, the subsequent 
intrusion of contaminated air being prevented by a ring of cotton-wool. Thirteen 
months afterwards the infusion, greatly concentrated by evaporation, exhibited its 
pristine deep transparency. A second similar group of tubes was charged with alkalized 
hay-infusion on the 27th of last January, and on the 5th of December (that is to say, 
after a period of more than ten months) the infusion was found perfectly clear. 
A number of hermetically sealed tubes charged with the same infusion, and boiled 
for only three minutes, have maintained for more than a year both their primitive 
transparency and their water-hammer sound. Thus many of the earliest experiments 
of the present year and the whole body of last year’s experiments are in complete 
harmony with each other. 
This harmony was, however, disturbed by some of the foregoing experiments with 
bulbs and tubes, and it was soon to be further disturbed by experiments with closed 
chambers. On the 6th of October, 1876, for example, an infusion was got ready in 
* Briefly described in the Introduction. + Phil. Trans, vol. clxvi. p. 50, and § 12 of this memoir. 
MDCCCLXXVII. 2 A 
