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ONTANAESTHE TICS 163 
family, was killed by the same percentage in four minutes, and, the chest being 
at once opened, the heart was found to have entirely lost its irritability, failing 
to contract when pricked with a needle. This percentage, then was clearly 
within Paul Bert’s mortal zone for these white mice. Four per cent. (4.9 being 
the extreme lower limit of Paul Bert’s zone maniable for the mouse) caused 
complete anaesthesia in three minutes and a half in another of the young 
animals ; and this atmosphere being continued in operation produced a pro- 
gressively lowering effect upon the breathing, which was reduced in the course 
of one hour and twenty minutes from two hundred per minute to twenty-eight 
shallow and irregular respirations, after which the animal died. The heart was, 
however, found beating when the chest was opened twenty minutes later, and 
the exposed organ continued to pulsate even for another hour, showing how 
little its power had been affected by the chloroform in the more diluted state. 
The experiments being continued on the following day, three per cent. of 
chloroform rendered one of the young animals completely passive in two minutes 
and a half; and within four minutes it had brought the respirations down to 
seventy-eight, and in the course of one hour and three-quarters reduced them 
to about twenty feeble and irregular movements, after which they ceased 
entirely, and did not recur, although the animal was withdrawn from the cham- 
ber within two minutes and a half of their cessation. The more rapid anaes- 
thesia and greater depression of the respiration occasioned by this smaller 
percentage of chloroform are, I believe, to be explained by a feeble state of the 
animal, caused by its having been the subject of the first experiment on the 
previous day. The fact illustrates the different susceptibilities to chloroform 
that may be presented by the same individual under different circumstances. 
Two per cent., tried with another of the young mice, made the animal 
stagger in about two minutes, but failed to produce complete anaesthesia in 
an hour ; and at that time the respirations continued as high as one hundred and 
sixty per minute. But after the lapse of another hour anaesthesia was found 
to be complete, and the respirations reduced to eighty-six. In the course of 
two hours more the breathing was further lowered to fifty-six, and it was evident 
that death would occur in no long time if the animal were kept in the same 
atmosphere. It was removed, and recovery took place, but only very slowly, 
no movement of the limbs showing itself for nearly an hour. 
Lastly, a percentage intermediate between those of the last two experiments 
was tried, viz. two and a half. It produced anaesthesia somewhat slowly in 
the young animal subjected to it, requiring a quarter of an hour for complete 
relaxation. The respirations meanwhile had come down from about two hundred 
to one hundred and sixty-eight, and, after the lapse of twenty-two minutes more, 
had fallen to one hundred and four. The animal was now left unobserved in 
the chamber for another hour, and at the end of that time it was found dead. 
It will be observed that two and a half per cent., though it anaesthetized more 
slowly, yet killed sooner than four per cent. had done on the previous day. 
The subject of the experiment had, I fear, been weakened by being kept in 
less favourable hygienic conditions since it was got from the dealer the day before. 
The facts elicited by these experiments, though not numerous, seem to me 
instructive. In the first place, they afford an illustration of Dr. Snow’s impor- 
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