THE FROG'S HEART 251 



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

 fore 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 



FIG. 213. 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.) 



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: 



Rate per Time of systole Timeof diastole Time of pause 

 minute in seconds in seconds in seconds 



Auricle 



Ventricle 



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



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

 move it completely from the body by first cutting the arteries at their branch- 

 ing in front of the bulbus arteriosus, then carefully lifting up the parts of 

 the heart and cutting away the great veins where they enter the sinus. This 

 will remove the entire heart, including all its contractile parts. The frog's 

 heart, when thus removed and still wet with its own blood, will continue con- 

 tracting rhythmically and in its natural sequence for some hours. Place 

 such an isolated heart in a watch-glass and take a record of its contractions 

 by the apparatus described in the preceding experiment. (The same phe- 

 nomena may be studied on a heart isolated and mounted in a Williams' 

 apparatus.) 



