the intervals of successive dots 120 second apart. The records show the auricular contraction preceding the ventricular. The period of a complete cycle is much longer in tortoise. The total period is 34 dot-intervals, or 1.7 seconds. In the particular specimen of frog the total period is represented by 14 dot-intervals or 0.7 second, while in the fish it is 16 dot-intervals or 0.8 second. Again in tortoise after the commencement
Fig. 121. Characteristic cardiograms of tortoise, frog and fish. The successive dot-intervals represent 0.05 sec.
of the less pronounced systolic contraction of the auricle, the contractile wave reached the ventricle in the course of 0.6 second, whereas in the frog and in the fish the interval is only 0.2 second, or one-third that in tortoise. The records show other characteristic differ-
