THE FROG S HEART 



227 



tracing of the movements of the lever of the recording tambour on the smoked 

 paper of the kymograph. The kymograph cylinder should travel at the rate 

 of about two to three centimeters per second. Take the time of the move- 

 ments of the kymograph by means of an electric magnet connected with an 

 electric clock beating seconds. After the record is secured the proper de- 

 scription should be written with a pencil on the smoked paper, and the paper 

 removed from the kymograph carefully and the whole record fixed in shellac. 



When the record is dry, count the rate of the heart-beat from the record 

 and measure the time of the cardiac systole and diastole, and the time of 

 pause at the end of the diastole. If these facts are taken from records secured 

 under different conditions of exercise, etc., as outlined in the preceding ex- 

 periment, then they may be brought together in a table for convenience of 

 inspection. A comparison of such results will usually show that with the 

 higher heart-rates the decrease of the time of the cardiac cycle is at the ex- 

 pense of the time of the diastole; in other words, the time of the systole re- 

 mains fairly constant while the time of the diastole increases or decreases 

 with the rate, a fact to which Hiirthle has drawn attention, figure 157. 



3. The Rate and Sequence of the Contractions of the Frog's 

 Heart. Destroy the brain of the frog and open the thorax, but do 

 not destroy the pericardium. Count the rate of the heart per minute, then 



FIG. 2ii. Heart Lever for Frog or Turtle Hearts. 



remove the pericardium and make a second determination after the heart is 

 exposed to the air. The different parts of the heart when exposed are easily 

 identified and the contractions which take place in definite sequence can be 

 determined without difficulty. Make this determination for the ventricle, 

 auricle, and sinus venosus by direct observation. 



