90 ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



The wires should now be reversed to show the cathodal excitation 

 on the making and the cathodal depression on the breaking of the con- 

 stant current. 



6. Action of Chloroform and Ether. Excise two frogs' hearts and 

 place each in a watch-glass. Cover them equally with a sufficient 

 quantity of saline solution (5 c.c.). Add a drop of pure chloroform to 

 one and a drop of ether to the other. Note that the heart in the former 

 solution loses its tonus rapidly and soon ceases to beat, while the action 

 of the other does not seem to have been materially impaired. In order 

 to produce the same effect with the ether, as many as 10 drops might 

 have to be added to the original solution. 



7. Dissection of the Mammalian Heart. Procure the heart of an ox 

 or sheep. Ask to have the " tubes cut long." Identify its different parts 

 and test the relative thickness of the walls of its chambers. What is 

 the functional significance of this difference in the volume of the mus- 

 cle substance? Identify the aorta, pulmonary artery, venae cavse, and 

 pulmonary veins. Note the appearance and strength of the walls of 

 these blood-vessels. Trace the coronary arteries from the arch of the 

 aorta and identify the coronary sinus. 



Explore the auricles and ventricles by inserting the index-finger 

 through the stumps of the different vessels. Palpate the interauricular 

 septum and locate the fossa ovalis. Slit open the two auricles and ex- 

 amine their walls and recesses. Note that the venous orifices are not 

 guarded by valves. 



Beginning at the apex of the heart make a series of transverse sec- 

 tions until both ventricles have been opened. Note that the left cavity 

 is incised first and possesses a much thicker wall than the right. Obtain 

 an unobstructed view of the tricuspid and mitral valves by making a 

 longitudinal incision through the wall of each ventricle. Study the 

 appearance and distribution of the papillary muscles, columnse carnese, 

 moderator bands, and chordae tendinese. Approximate the valve flaps 

 and note the manner of insertion of the chordee tendinese. Trace the 

 course of the bundle of His. 



Tie a short glass funnel in the stump of the ascending aorta. Hold 

 the heart vertically and pour water into the funnel. Observe that the 

 semilunar valve closes, thereby preventing the water from escaping 1 into 

 the left ventricle. By means of a long probe push one of the flaps aside. 

 Note the rush of water into the ventricle. This condition represents 

 aortic insufficiency (regurgitation). Repeat the experiment on the 

 right side. The sinuses of Valsalva are here more prominent, because 

 the vessel wall is much thinner. 



