TRANSACTIONS OF SECTION I. 631 
By commencing with small doses and gradually increasing their size, 
animals of 5 to 12 kg. body weight have, in the course of an experiment 
lasting one and a half hours, been rendered so immune to the ill-effects of 
the drug as to tolerate as large a quantity as 04 gramme injected intra- 
venously without other apparent ill-effects than a lowering of blood-pressure, 
from which recovery gradually takes place. 
The commencing dose varied from 0:025 mg. to 0°5 mg. of atropine, 
hyoscine, &c., an injection being given every three to ten minutes after- 
wards until the animal succumbed. In some cases 0°5 mg. as an initial dose 
caused death rapidly, but in others 1 mg., or even 2 mg., could be used 
as an initial dose without a fatal result, the animal showing the same 
idiosynerasy as the human subject in this respect.. In all cases where the 
initial dose failed to kill, each successive dose was doubled or trebled, 
until on many occasions 04 of a gramme of the alkaloid was given, and 
the animal kept alive by artificial respiration, the blood-pressure, which 
was very low after the injection, rising almost to the normal. But imme- 
diately on stoppage of artificial respiration the pressure would fall and 
death ensue. In later experiments animals have survived this dose without 
having recourse to artificial respiration. 
In my earlier experiments it was impossible to make any definite 
statement as to the permanent effects of such a dose, as in this and all 
other cases the animal was killed without being allowed to wake from 
the anesthetic. Now, from a further series of experiments it has been 
ascertained that this immunity applies to the remote as well as to the 
immediate effects, a number of animals who have received large quan- 
tities of the drug—viz., 11 to 12 grs.—being allowed to live for different 
periods afterwards, some as long as eight days. These animals were then 
again anvesthetised and an intravenous injection of atropine, of the same 
amount as the largest dose given at the previous séance, administered. 
The animals all survived this dose, which in some cases amounted to 
7 grs., thus showing that the immunity lasts for some time. 
It does not make any difference which of the drugs, atropine, hyoscine, 
hyoscyamine, duboisine, daturine, or scopolamine, are used to commence 
with in the process of obtaining this tolerance; any one can be used in 
increasing doses; then, when the dose has become large, an increased dose 
of any of the others given with no different result than would be obtained 
were the first drug continued, each drug immunising the animal from all 
the rest of the series. Further, the serum of an animal which has been 
rendered immune to large doses of these drugs will, if injected into another 
animal, confer an immunity on it: 
Action of Atropine in Chloroform Poisoning.—‘ When the _ blood- 
pressure has been depressed by an overdose of chloroform, section of the 
two vagi, by cutting off the medullary effect, will release the heart; the 
beat will once again recover its normal character, and the blood-pressure 
will bound up.’? A natural inference would be that atropine, by cutting 
off the tonic effects of the vagus, would have a similar effect. This, how- 
ever, has not been the case in my. experiments.” In chloroform poisoning, 
just as in the normal condition, atropine does not raise the blood- 
pressure, but lowers it. I have not found the slightest benefit to accrue 
when atropine has been administered to an animal whose circulation is 
depressed with chloroform or other anesthetic. 
The use of atropine prior to the administration of chloroform has been 
strongly advocated and no less strongly opposed by various writers, e.g., 
1 Dixon, op. cit. x 
?T have not invariably found benefit from cutting the vagi, though often, 
as Dixon states, it restores blood-pressure. In the case of one animal, although 
a sudden rise of blood-pressure took place, respiration was not restored; the 
blood-pressure again fell, and death rapidly ensued, 
