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Transactions of the Royal Society of South Africa. 
pericardium tied round it. The rate and volume of the heart were thus 
recorded. 
Results. — With small doses the heart is slowed and systole increased, 
and the heart empties itself more completely at each beat. With fatal 
doses the slowing is very transient and soon gives place to quickening and 
irregularity, with onset of fibrillation and arrest of the heart in one or two 
minutes. In one case well-marked heart-block was seen. The action of 
slang-kop on the mammalian heart in sitil differs from its action on the 
frog's heart and also the isolated mammalian heart in that the heart in situ 
is arrested in diastole. The preliminary slowing has a different cause from 
the slowing seen in the isolated mammalian heart, which can only be due to 
an action of the drug on the heart itself or the vagus terminations in the 
heart. The slowing in the intact animal is not seen if the vagi nerves be 
cut, and is therefore due to direct stimulation of the vagus centre by the 
ABC D 
Fig. 3. 
toxic substance, or to indirect stimulation following the rise of blood- 
pressure as in the case of adrenalin. Fig. 8 shows the movements of 
the heart of a cat (weighing 2340 grm.), recorded with the cardiometer. 
The downstroke denotes systole. a is the normal heart-beat. b shows 
the movements one minute after injecting 0*5 c.c. of tincture of Urginea 
Burlcei into the jugular vein : the heart is slowed, and systole and diastole 
are increased. c shows the effect at the end of two minutes, d shows the 
terminal fibrillation, beginning in three minutes, and arrest of the heart in 
diastole in less than four minutes. 
(e) Effect on Blood-pressure. 
In most of the experiments the blood-pressure from the carotid artery 
and the heart-volume, as shown by the cardiometer, were recorded simul- 
taneously. After injection of slang-kop there is a large and persistent rise 
of blood-pressure, commonly equal to 50 or 60 mm. of mercury, but some- 
times much more. With the onset of irregularity the blood-pressure falls. 
