RECORDING HEART TRACINGS 



69 



tions respectively? In which direction does the lever move 

 in systole? 



Take several rows of tracings, lowering the drum suf- 

 ficiently to leave about three-eighths or one-half inch be- 

 tween each row of tracings. The record should thus read 

 from left to right and from bottom to top. As the ether 

 is dropped on, the action on the systole of the heart will 

 soon become apparent. This should progress until the 

 heart almost stops. Then irrigate the heart with normal 

 salt solution a while and see if you can get it to recover. 

 Stimulate the vagus from time to time and see if the power 



S^T", Ax Carotid Arch 



Riaftt 



Systemic- * 

 arch 



Pulmo- - 

 cutaneous arc/) 



H/<7/jf Auricle 

 Truncus arteriosus 



Left Ant. Caval 



-Left Auricle ' 

 Pulmonary Vein '\ $ 



-Ventricle 



Rn/ht Carotid 

 / arc/? 



RiqM Systemic 



arch 



Richt Pulmo - 

 cutaneous arch 



Right Ant 

 Cava/ Vein 



Opening of 

 Sinus venosus 

 into the Right 

 Auricle 



-Sinus venosus 



Post Cavd vein 



Fig. 65. The anatomy of the frog's heart. (Modified from Wiedersheim. ) 



of inhibition is lost. How has the drug affected the heart? 

 Is the innervation of the organ involved in the action or 

 is this mainly a muscular affair? Does this experiment 

 show any action of the drug on the cardie-inhibitory center 

 in the medulla? When the heart tracings are finished then 

 record the time in five second intervals in two or three 

 rounds on the drum. These time records also serve as 

 comparison lines to determine whether or not there has 

 been an increase or a decrease of tone in the heart muscle. 

 What effect would a decrease in heart muscle tone have 

 on the position of the record with reference to a horizontal 

 line drawn around the drum? 



