Page:Collected Physical Papers.djvu/390

370 The characteristics of contractility and conductivity are thus shown to be exhibited not only by animal but also by plant tissues. In the animal the cardiac tissue exhibits automatic and rhythmic pulsations. In the plant a similar activity is manifested by the leaflet of Desmodium gyrans, the well known Telegraph plant.

The record of the pulsation of the animal heart by the Cardiograph labours under the unavoidable difficulty of continuous frictional contact introducing error in the correct record of the amplitude and time-relations of the heart-beat. The drawback of continuous contact has been removed in my Resonant Cardiograph which records the pulsation with great precision by means of periodic dots, the Cardiogram being also its own chronogram. The automatic method of registration of extremely short intervals of time can be utilised with great advantage for this and other investigations.

The Resonant Cardiograph inscribes the different phases of the heartbeat with unprecedented accuracy. The systolic contraction and its persistence, the diastolic expansion and the subsequent pause, and any variation of these under external agencies, can thus be quantitatively determined. The cardiograms of different animals show, moreover, certain characteristic differences in regard to time-relations, as illustrated by records of tortoise, of frog and of Ophiocephalus fish given below.

The writing lever was tuned to vibrate 20 times in a second, the magnification produced being about 8 times. The time-relations, it is to remembered, is found from