Page:Collected Physical Papers.djvu/392

372 and give very striking visual demonstration of the relative activity at different phases of the pulsation. When the activity is very great the markings are very wide apart and the dots are lengthened into dashes; with slowing down of activity the dots become thin and drawn close together (fig. 121). Under the action of depressing agents the post-diastolic pause becomes greatly prolonged.

I have demonstrated elsewhere the remarkable similarity of rhythmic mechanism in animal and plant. In both, lowering of temperature slows down the pulsation culminating in an arrest. Rise of temperature up to an optimum, on the other hand, enhances the frequency. Diminution of internal pressure causes an arrest in both. The rhythmic tissue in animal and plant, has a long refractory period. In both, application of external stimulus has no effect during systolic phase of contraction, whereas an extra-pulsation is produced by stimulus during the diastolic phase of expansion.

The effect of drugs is often remarkably similar in the two cases. Dilute solution of potassium bromide causes a depression of cardiac pulsation; this depression is removed by the physiological antagonism produced by certain drugs.

I have recently been engaged in investigating the action of various medicinal plants of India on the activity of the animal heart. Among these I find that a heart in a state of depression is greatly stimulated by extracts pf Abroma augusta.