228 



THE CIRCULATION OF THE BLOOD 



Prepare a cardiac lever as shown in figure 211, taking special care to ar- 

 range the foot so that it will not bind on the lever when in motion. Adjust 

 the foot of the lever on the exposed ventricle and bring its point to write on 

 the smoked paper of a recording cylinder. This cylinder should travel at 

 the rate of about i cm. per second and its speed be determined by the writing 

 point of an electric magnet which is connected with the electric-clock circuit 

 marking seconds. Take care to adjust the time magnet in a vertical line 

 with the writing point of the heart lever, placing the heart lever about i cm. 

 above the magnet lever. The tracing of the ventricle's movement, or cardio- 

 gram, will show alternate contraction, relaxation, and pause of the ventricle. 

 It will also enable one to measure the exact proportion of the total time of the 



FIG. 212. Cardiogram Showing Contractions of the Auricle, a, and Ventricle, v, of a Frog. Time in 

 seconds. The record shows the sequence of the auricle and ventricle. (New figure by Dooley.) 



cardiac cycle consumed by the systole and diastole, and also that portion of 

 the diastole in which the ventricle is wholly at rest. 



After one has obtained the ventricular tracings and has learned the diffi- 

 culties of adjusting the apparatus, a second heart lever should be adjusted 

 so that its foot rests upon the auricle, and the auricular movements may 

 therefore be traced on the smoked paper of the recording cylinder at the same 

 time as those of the ventricle. If some care is taken to adjust these two 

 writing points in a vertical line a splendid tracing showing synchronism 

 between auricle and ventricle is obtained. Measure the rate and the time 

 of the different phases of the contraction of the auricle and ventricle and 

 tabulate them in the following form, always expressing fractions in the 

 decimal system: 



4. The Contractions of the Excised Heart of the Frog. Pith a 

 frog and expose the heart, as described in the preceding experiment. Re- 



