ELEMENTARY EXPERIMENTAL PHYSIOLOGY 55 



5. Dissect the heart of a dead frog. Identify the sinus, auricles, 

 ventricle and bulbus arteriosus (Figs. 52 and 61). 



Thrust a small test-tube down the gullet to stretch it, and dis- 

 sect out the vago -sympathetic nerve and 

 follow its cardiac branch down to the 

 heart. 



The inspection of the frog's heart in 

 action (p. 61, Lesson XIV. I.) may with 

 advantage be taken here if the supply of 

 frogs is sufficient. 



II. The External Manifestations of the 

 Cardiac Cycle in Man 



FIG. 52. Heart of frog 

 from behind. 



1. Ventricle. 



2. Auricle. 



3. Crescent. 



4. Sinus. 



5. Great Veins. 



6. Aorta. 



1. The Cardiac Impulse Cardiograph. 



Get ready and study the mode of action 

 of a cardiograph (Fig. 53), which should have a long lever on the 

 recording tambour. 



(1) Find the position of the cardiac impulse on the front of the 

 chest of a fellow student and investigate its characters. 



(2) Mark its position with an aniline pencil and then apply the 

 cardiograph with the button upon the impulse. Adjust the pressure 



FIG. 53. Marey's cardiograph. 

 The tube is connected with a recording tambour. Pressure is adjusted by the screw and spring. 



of the button by means of the screw till the lever gives the largest 

 possible excursion, and take a tracing on a slow-moving drum. 

 This is best done with the subject seated and leaning forward and 

 to the left. The breath may be held in expiration for a few seconds. 

 Take a time tracing in T \,- seconds. Make an enlarged drawing of a 

 part of the trace and try to explain the various elevations and 

 depressions. 



