200 
Tranmrt 10)18 of the Royal Society of South A frica. 
The first offoct i.s an iiiereaso in the extent of systole. Very soon the 
rhythm of tlie lieart. is slowed. The output per minute, measured by the 
outflow from the aortic cannula, is increased. The slowing- becomes more 
marked, and after some time the relaxation of the ventricle is impaired and 
the output of the heart decreases. These chan^^es continue, gradual increase 
in the contraction and slowing and diminution in the diastolic relaxation 
and outflow, until the heart is finally arrested in complete systole. 
Fig. 1 shows the effect of perfusing the isolated frog's heart with 1 in 
.5000 extract of Urginea Burl-ei. a is the normal heart-beat, b to h are the 
effects produced at three-minute intervals after perfusion. The heart is 
stopped in 21 minutes in systole. 
A 13 C I) E F OH 
Fig. 1. 
(1)) Action on the Frorft^ Heart in situ. 
The tracings obtained from the frog's heart in situ were practically a 
reproduction of those obtained from the isolated heart. With sufficient 
dosage there w^as stoppage of the heart, the ventricle in systole and the 
auricles in diastole. 
(c) Action on the Isolated Mammalian Heart. 
Eabbits, cats, rats and guinea-pigs w^ere used in the experiments. The 
animal was killed and the heart quickly removed. A cannula was inserted 
into the aorta and the heart perfused through the coronary arteries with 
oxygenated Locke's solution at 37° C. The tip of the ventricle was 
attached to a lever writing on a smoked drum. 
The first effects noticeable on adding tincture or extract of slang-kop to 
the perfusing fluid are increase in systole and diastole and slight slowing. 
The subsequent events follow one of three courses*: (1) The heart remains 
slow but regular ; the extent of systole increases, while that of diastole, after 
the preliminary increase, decreases until the heart is arrested in systole like 
