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PROFESSOR TYNDALL ON THE DEPORTMENT AND VITAL 
its pipette-shank filled with air. In a fourth chamber only one inch of the pipette-shank 
was filled with air ; here one out of a total of three tubes remained pellucid. Thus, where 
the closure above was perfect, we had in this instance perfectly pellucid infusions ; where 
it was grossly defective, the infusions gave way in all the tubes ; while where the closure 
was but slightly defective we had the escape of a fraction. 
The defects thus revealed came doubtless into play when the infusions were intro- 
duced, the descending column of liquid sucking in minute air-bubbles between the 
india-rubber tubing and the pipette, thus carrying with it the external contagium. Few 
are aware of the precautions essential to save the experimenter from error in inquiries 
of this nature. Even with some of our best and most celebrated observers I find no 
adequate sense of the danger involved in their modes of experimentation. 
§ 14. Experiments in the Boy at Gardens , Kew. 
But it was only in exceptional instances, dependent on the state of the air, that even 
precautions such as those described in the foregoing section secured freedom from con- 
tamination. The contagium seemed omnipresent and persistent, and whether it was local 
or general — due to the accidental condition of our laboratory, or to an epidemic of the air 
— became a question with me, not by any means to be decided offhand. On this point, 
then, I held judgment in suspense. The infection was, to all appearance, fully accounted 
for by reference to the conditions under which I worked ; but as regards outbreaks of 
epidemics the autumn had been a remarkable one, and it seemed well worth investi- 
gating whether it was not also a period prolific generally in the germs of putrefaction. 
I resolved therefore to break away wholly from the Royal Institution, and, thanks to 
the friendly permission of the President of the Royal Society, I was enabled to transfer 
my apparatus to Kew Gardens. By the enlightened munificence of Mr. Jodrell, a new 
and very complete laboratory had been just erected there, and in it I sought a purer air 
than I could find at home. 
My chambers hitherto had been constructed of wood, but those to be tested at Kew 
were made of block-tin, and they were carried direct from the tinman’s to the gardens 
without being permitted to come near the infected air of Albemarle Street. At Kew 
the test-tubes employed were first cleansed with carbolic acid, then washed with a 
solution of caustic potash, afterwards swept out with distilled water, and finally raised 
almost to the temperature of redness by a Bunsen-flame. They were then fitted air- 
tight into the chambers with white-lead and tow. 
The chambers were closed on the 3rd of January, and allowed to remain quiet until 
the 8th, when the two most refractory liquids that I had encountered in the laboratory 
of the Royal Institution were introduced into them. These were infusions of cucumber 
and melon. There were two chambers devoted to each infusion — four in all ; and 
each chamber embraced three large test-tubes. The period of boiling w r as that found 
effectual last year, i. e. five minutes. The temperature of the room in which the 
chambers were placed was maintained, partly by hot-water pipes and partly by a 
