262 



THE CIRCULATION OF THE BLOOD 



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

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

 to the auricle, and the auricular movements recorded 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 



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.) 



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

 different phases of the contractions of the auricle and ventricle and 

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

 decimal system: 



4. Sequence, Conduction and Heart Block, Turtle Heart. Prepare a 

 turtle, expose the heart and determine the rate and sequence of the 

 parts. Observe that the veins are contractile. 



a. Make simultaneous records of the right auricle and the ventricle, 

 use speeds of 2 mm. and 2 cm. per second. 



b. Attach a GaskelPs clamp close against the ventricle in the a-v 

 groove. While taking records slowly compress the clamps by steps until 

 the ventricular rhythm begins to slow down. Produce partial block 

 through 2 auricles to i ventricle, 3 to i, 4 to i, etc., rhythms, until com- 

 plete block is obtained. Note recovery on removing the clamp. 



c. While recording the contractions of the right and left auricles by 

 separate levers split the heart into right and left halves. The right half 

 will continue the usual rhythm, the left will be slower but show more 

 tone. These halves will respond to nerve control and to block tests. 



