194 
PEOFESSOB TYNDALL ON THE DEPOETMENT AND VITAL 
necks were so bent and plugged with cotton-wool that no impurity from the wool could 
fall into the infusion. Four bulbs were charged with an infusion of Heathtield and 
four with an infusion of London hay, samples of the same infusions being introduced 
at the same time into another series of bulbs which were plugged like their neighbours 
and subjected continuously to the boiling temperature for ten minutes. The eight 
bulbs first referred to were, on the contrary, discontinuously boiled, the sum of their 
periods of boiling being four minutes. The result is that while the entire series of 
bulbs boiled for ten minutes gave way within forty-eight hours after their preparation, 
seven out of the eight bulbs which had been subjected to discontinuous boiling remained 
permanently brilliant. 
On the 3rd of February, with the view of testing the new method still further, 
infusions of our most refractory kinds of hay were prepared. There were five bulbs of 
neutralized Guildford infusion, and five of a neutralized infusion formed from a mix- 
ture of old Colchester and old Fleathfield hay. Two bulbs of each infusion were at the 
same time charged and subjected to the boiling temperature for ten minutes. The ten 
bulbs first mentioned were never raised to the boiling temperature at all, the maximum 
to which they were exposed being some degrees below their boiling-point. The result 
is that while every one of the four bulbs boiled for ten minutes has become turbid and 
covered with scum, one only of the ten discontinuously heated bulbs has given way ; 
nine of them remain as brilliant as at first. 
It is obvious from what has gone before that two hundred and forty minutes might 
have been substituted for ten minutes without altering this result. Five minutes of dis- 
continuous heating can accomplish as much as five hours continuous heating. 
On the same date three bulbs charged with an acid infusion of London hay were 
subjected to the same discontinuous treatment. They all remain brilliant to the 
present hour. 
On the 7th of February four of Cohn’s tubes were charged with turnip-infusion, 
which was heated discontinuously night and morning up to a temperature of 205° 
Fahr. The total time during which they were exposed to this temperature was about 
three minutes. They were permanently sterilized, and exhibit a singular brilliancy 
to the present hour. 
The discontinuous method of heating has also been applied with success to the 
closed chambers. One mode of operation is this : — An oil-bath is heated to a tempe- 
rature of 300° Fahr. The charged test-tubes of the closed chamber are then plunged 
in the oil, which clasps the tubes to the level of the surface of the infusion. They are 
either raised to incipient boiling and then removed, or suffered actually to boil for thirty- 
seconds and then removed. Another mode of heating is this : instead of being plunged 
into hot oil, the test-tubes are plunged for two or three minutes into boiling water, taken 
ou t, wiped dry, the actual boiling being finished by a spirit-lamp. This is a very handy 
method, and more under the experimenter’s control than the oil-bath. When the latter 
is employed the infusions sometimes in great part waste themselves by leaping from their 
