PERSISTENCE OP PUTREFACTIVE AND INFECTIVE ORGANISMS. 
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nor in that of the cucumber could the water-hammer sound be obtained from the cloudy 
flasks, and when their sealed ends were broken under water, the vacuum was found 
defective. In the clear tubes, on the contrary, it was found practically perfect. 
Again, on the 20th of November, seventeen retort-flasks were charged with infusions 
of turnip, cucumber, and parsnep. They were boiled for three minutes in an oil-bath, 
and carefully sealed while boiling. The six turnip-flasks remained permanently clear, 
maintaining for months their sharp water-hammer sound. Of the five parsnep-flasks, one 
became turbid and four remained permanently clear. These latter only yielded the 
water-hammer sound. The turbid flask, on the contrary, when shaken yielded no such 
sound, and when its sealed end was broken under water, its vacuum proved defective. 
Of the six. cucumber-flasks, two became turbid, the remaining four being perfectly 
clear. On breaking their sealed ends under water, one third of one of the turbid flasks 
and one fourth of the other remained unfilled by the liquid. 
On the 6th of December eighteen retort-flasks were charged with cucumber-infusion. 
They were boiled for the usual time, that is three minutes, extreme care being taken to 
seal them during the issue of the steam. The water-hammer sound in all these flasks 
was particularly sharp and clear. Exposed to a temperature of 90° Fahr. for many 
weeks, seventeen of them remained perfectly pellucid ; while the same infusion in a 
sealed bulb with filtered air above it and dissolved in it swarmed with life after boiling 
for sixty times the interval here found effectual. 
On the day subsequent to its preparation, one of these well-exhausted flasks was 
unexpectedly found turbid and covered with scum. But on examining the sealed end 
it was found snipped off. The laboratory air had thus entered the flask and given birth 
to the observed organisms. Failures of this sort have a demonstrative force greater even 
than successes ; they render so obviously plain the external source of the contamination. 
It is worth saying here that the observation just recorded was of frequent occurrence. 
The fineness of the sealed points of our retort-flasks renders them very liable to be 
snipped off if they are not handled with care. After preparation they are usually sus- 
pended on a wire or on a wooden support ; and in frequent instances, after such suspen- 
sion, I have found a flask differentiating itself by thick turbidity from a number of per- 
fectly pellucid neighbours, the yielding of the flask being immediately traced to the 
fracture of its sealed end. 
With the view of showing how readily, unless extreme care is taken, contamination 
may enter hermetically sealed vessels, the following experiment was made on the 6th of 
December. Four retort-flasks were charged with the cucumber-infusion, boiled for the 
usual time and sealed, not during the outrush of the steam, but a moment after ebulli- 
tion had ceased. On the 9th of December three of these four flasks were faintly but 
distinctly turbid. The reason is obvious. On the cessation of the ebullition, a 
momentary condensation of the steam above the infusion caused an indraught — slight, 
no doubt, but still sufficient to contaminate or vivify the infusion. 
The source of the contagium was also indicated by the following experiments. A 
2 f 2 
