PEESISTENCE OF PUTREFACTIVE AND INFECTIVE ORGANISMS. 
153 
§ 3. Hay-inf usions. Preliminary Experiments with Pipette-bulbs. 
I have now the honour to submit to the Royal Society an investigation which embraces 
among others the points here referred to, and which has proved far more difficult and 
laborious than I expected it would be. On the 27th of September, 1870, a quantity of 
chopped hay was digested for three hours and a half in distilled water maintained at a 
temperature of 120° Fahr. The infusion was afterwards poured off, and its specific 
gravity reduced to the exact figure given by Dr. Roberts, viz. 1006. It was then 
filtered and slightly superneutralized. Precipitation occurred on the addition of the 
potash, and the infusion was boiled for five minutes to render the precipitation com- 
plete. It was then refiltered, and introduced into a series of bulbs of the same size and 
character as those described by Dr. Roberts, and called by him “ plugged bulbs”*. 
Each bulb was a cylinder about four inches high and upwards of an inch wide, 
Avith a long neck attached to it f , as shown at A, fig. 2. Two thirds of the cylinder 
were occupied by the infusion. After the introduction 
of the latter, the neck of the bulb was plugged with 
cotton-wool, and hermetically sealed above the plug, 
as at B, fig. 2. The bulbs were afterwards plunged 
in water deep enough to cover their necks, which was 
gradually raised to the boiling-point, and maintained 
at the boiling temperature for ten minutes. They 
were then removed and permitted to cool; after 
which the sealed end of each neck was broken off 
by means of a file, its subsequent appearance being 
shown at C, fig. 2. The bulbs, protected by the 
cotton-wool plugs in the neck above them, were then 
exposed to a tolerably uniform temperature of about 
90° Fahr. 
At the same time two similar bulbs, charged with 
the same infusion, had their necks bent dowmvards, 
as in fig. 3 (p. 6), the inclined portion being plugged, 
so that no impurity could fall into the liquid from 
the cotton-wool. These two bulbs were boiled for five minutes in an oil-bath, and 
plugged while boiling with cotton-Avool. They were then sealed behind the plugs and 
permitted to cool, their sealed ends being broken off afterwards. 
On the 30th of September the infusion in all the straight-necked bulbs was turbid, 
while in the two bent-necked ones it was perfectly clear. On the 2nd of October 
* Phil. Trans, vol. clxiv. p. 460. 
f I have called them pipette-bulbs because they are formed by hermetically sealing one shank of a pipette, 
close to the bulb, leaving the other shank open for the introduction of the infusions. German pipettes, on 
account of their cheapness, were at first commonly used ; hut in cases of long-continued boiling, explosions were 
so frequent that bulbs of English glass of specially resistant quality were resorted to. 
