1910. | Action of South African Boxwood. 290 
case that the heart was not appreciably influenced, even when doses of 
boxwood were given sufficient in amount to paralyse completely the brain 
and medulla. From experiments with the cardiometer (fig. 3) 1t is obvious 
that the administration of the drug is followed by a period in which the 
output of blood from the heart per minute is actually greater than the 
normal, and in no case has a diminution in the output been observed. It 
will be seen from this figure, which is quite typical, that it is the strength 
of the systole which is especially increased, and that the effect is prolonged. 
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Fi@. 3.—Cat. Urethane. Cardiometer and blood-pressure. Shows the effect of injecting 
10 milligrammes of alkaloid. Note increased cardiac output and augmentation ‘of 
systole. Time, seconds. 
At first sight it might seem that these experiments with the isolated heart 
and with the cardiometer are contradictory, but such is not the case, since 
any drug which produces a pure vaso-dilatation causes secondary effects on 
the heart, which result in an augmented output of blood per minute; thus 
nitrites depress the isolated heart, as indeed they do all muscle tissue, yet 
when taken by an intact animal the cardiac output is increased. All the 
isolated heart experiments teach is that boxwood exerts no direct stimulant 
action on cardiac muscle. Even when natural respiration has ceased in an 
animal as a direct result of boxwood poisoning, additional doses of the 
VOL, LXXXIII.—B. Z 
