630 TRANSACTIONS OF SECTION I. 
of the fluid in which the drug is dissolved, since an injection of an equal 
quantity of normal saline solution has been always found to induce a 
rise of pressure similar in character and of equal magnitude. 
Of course, the effect of atropine on the blood-pressure has almost always 
been recorded in animals already under the effects of other drugs. Thus the 
animal has been under the effects of chloroform, ether, or A.C.E. mixture 
when the first dose of atropine, hyoscine, &c., has been injected, and in 
the experiment in which records of auricle and ventricle were taken, curari 
was administered in addition." On the other hand, many of the larger 
doses have been given when the animal has not had any anesthetic for 
the previous half-hour, the atropine already used sufficing to maintain an 
unconscious condition. 
Effect wpon the Heart.—Contrarily to the usually accepted view, it has 
been found that in dogs atropine has only at most a very slight and 
temporary effect in the direction of augmentation of the heart; the chief 
effect is a diminution in the extent of movement as revealed by the heart 
levers. 
Mode of Action of the Drugs.—The levers of the piston recorders con- 
nected with the limb plethysmograph and the intestinal oncometer always 
fall on the injection of the drug; the limb and intestinal tracings, in 
fact, passively follow that of the blood-pressure, and frequently show the 
same preliminary rise as does the blood-pressure. 
It would appear that rather too far-reaching deductions have been 
drawn from the action of atropine in cutting out the inhibitory control of 
the vagus. Since cutting the vagi always raises the blood-pressure, while 
the administration of atropine always lowers it-~in the dog, at any rate— 
and since on injection of atropine the volume of both limb and intestinal 
wall always follows passively the blood-pressure, we must conclude that 
atropine acts upon the heart in a manner quite different from that of 
section of the vagi. It seems, in fact, that with atropine, although the 
vagus inhibition is removed, there is a much more powerful effect acting 
upon the circulation in an opposite sense—namely, a paralytic effect on 
the heart muscle itself. Dixon says that the muscle of the frog’s heart is 
‘slightly stimulated. In a few experiments I have performed, I have not 
been able to verify this. 
Action on the Respiratory System.—It is well known that the first 
effect of atropine upon the respiration is to increase both the frequency 
and extent of the movements. Subsequently, however, the respiratory 
centre is paralysed.. I have been able to confirm the statement made by 
Reichert,” and quoted by Sollmann,’ that an animal may recover from 
many times the minimal fz tal dose if artificial respiration be maintained. 
This power of recovery on the part of the respiratory centre is of supreme 
practical importance in dealing with cases of poisoning by this drug. 
The Effects of rapidly repeated Doses of the Drugs.—It is well known 
that a very marked tolerance to atropine, as well as to other drugs, can 
be established both in animals and in man by gradually increasing the 
dosage over a period of days, weeks, or months. It is, however, somewhat 
surprising to find that within the limits of time occupied by a single 
experiment a dog can be brought to withstand, manifesting only a com- 
paratively slight reaction, a dose which, if administered at the beginning 
of the experiment, would have been certainly and quickly fatal. 
1 In one experiment I have reduced this objection to a minimum by employing 
only just sufficient anesthetic for the carrying out of the preliminary surgical 
proceedings. The animal was then allowed to recover from anesthesia, and 
atropine in a small dose injected into a vein. The effect in this case, as usual, 
was a fall and not a rise of blood-pressure, and the heart was weakened, 
* Reichert, Phila. Med, Jour., January 19, 1901. 
* Sollmann, op. cit. 
