June, 1951]
V.
B.,
J.
C.
D.
AND
V.
I.
97
minutes. In all cases the systolic level was found to be above normal, whereas
the diastolic level was greatly reduced.
Perfusion of the isolated frog's heart with 1 c.c. of 1 in 10,000 concentration
of gigantin in ringer, produced an immediate acceleration of the heart from 20 to
36 beats per minute. This is approximately 80 per cent increase over the normal.
The amplitude was diminished considerably due to the deficient relaxations, the
systolic level being normal. The concentration of the drug being toxic arrested
the heart in complete systole in three minutes (Plate VIII).
Perfusion with 1 c.c. of 1 in 100,000 concentration of the drug in the ringer
followed subsequently by normal ringer did not alter the rate or the amplitude to
any appreciable degree.
Continuous perfusion of isolated frog's heart with gigantin in a physiological
concentration of 1 in 5 million in the perfusion fluid decreased the rate and increased
the amplitude of the heart beat from the beginning, the increased amplitude being
due to the increased systolic excursions. No heart block and no contracture were
observed and the heart worked satisfactorily for more than an hour and a half (Plate
IX, and Table I).
The results of seven perfusions showed that 1 in 1 million concentration of
the drug, which was lethal in about 25 to 35 minutes, reduced both the rate and
the amplitude for the first 5 minutes. Then the rate continued to be lessened whereas
the amplitude was increased gradually due to the increase in the systolic level, the
diastolic level being normal. The heart was regular till the 6th minute, became
irregular afterwards due to the occurrence of heart block. It was finally arrested
in diastole (Plate X, and Table I).
Perfusion with 1 in 500,000 concentration of the drug in the perfusion fluid
did not produce any change in the rate for about a minute. This was followed by
a gradual slowing and arrest of the heart in about 18 minutes. The amplitude was
reduced to 50 per cent of the normal, the diminution being due to the deficient
relaxations. The systolic level was either normal or increased. The heart was
regular for the first few minutes. Then it became irregular due to the auriculo-
ventricular block, resulting in the arrest of the heart.
Still higher concentrations as 1 in 100,000 in the perfusion fluid, which was
lethal in 9 to 14 minutes, caused slowing of the rate and increase of the amplitude
from the beginning. Here again the increase was due to the increased systolic
excursions. But the diastole was deficient due to the inability of the heart muscle
to relax fully to the normal. The heart was regular till the 4th minute. Irregu-
larities in the form of extra systole were observed between the 4th and the 6th
minutes. Later heart block set in and arrested the heart in diastole (Plate XI, and
Table I).
A highly toxic concentration as 1 in 10,000 of the drug in the perfusion fluid,
which was fatal in 3 minutes, completely reversed the series of events. The heart
was accelerated from the beginning, the amplitude diminished till the end. The
systolic level was normal whereas at each successive beat the heart lost its power of
relaxation and stoped in complete systole. This phenomena has been termed as
' contracture ' and this resembles that of digitalis.