ELEMENTARY EXPERIMENTAL PHYSIOLOGY 79 



and prevents the escape of the water. Lay open the left ventricle in 

 the same manner as the right, carrying the first incision down the 

 left side of the ventricle. Observe the entrance into the aorta and then 

 lay this open. Note the orifices of the coronary arteries from the right 

 and left sinuses of Valsalva. 



Demonstration of Action of- Valves in the ox or horse's heart. 

 (Gad.) Two brass tubes with glass windows are tied one (7 cm. in 

 diameter) into the left auricle, the other (5 cm.) into the aorta. The 

 brass tubes are connected by side tubes to the bottom and top respec- 

 tively of a reservoir containing water. A small hole is made in the 

 apex of the heart, and a glow lamp is inserted into the left ventricle. 

 The wires of the lamp are connected with two Grove cells. A tube 

 connected with a rubber bag is tied into the apex. The bag is full of 



FIG. 77. Marey's Cardiograph. The tube is connected with a recording tambour. 

 Pressure is adjusted by the screw and spring. 



water. On compressing the bag the auriculo-ventricular valves close, 

 while the aortic valves open. On relaxation the aortic valves close, 

 while the auriculo-ventricular valves open (Fig. 76). 



The Cardiac Impulse. Observe and feel the seat of the cardiac 

 impulse when the subject is (1) standing erect, (2) lying horizontal on 

 the left, and (3) on the right side. The impulse is felt in the fifth or 

 fourth intercostal space about 1J inches below the nipple line, and 3J 

 inches from the mid-sternal line. It shifts under the sternum when 

 the subject lies on the right, and to the nipple line when he lies on the 

 left side. Owing to the influence of gravity, a different part of the 

 heart comes in contact with the chest wall in each posture. Apply the 

 button of the cardiograph to the seat of the impulse, and fix it with 

 tapes. One tape is fastened round the chest and one over the right 



