ACTION OF THE VALVES OF THE MAMMALIAN HEART. 181 



Finally, if the valves act as described in Landois and Stirling (3rd ed., p. 59) and 

 many other text-books, the ventricles can never be even approximately completely 

 emptied. A large supra-papillary space must always remain filled with blood. 



These considerations have led me to reinvestigate the question of how the auriculo- 

 ventricular valves are closed, and how they prevent the regurgitation of blood into the 

 auricles. 



It is at once obvious that these valves might fulfil their function of preventing 

 regurgitation in just as perfect a manner and without the severe strain, which, according 

 to the presently accepted theory, they have to bear with each systole, if, instead of being 

 raised to form a horizontal septum, their cusps were simply applied face to face to one 

 another. In this way all passage of blood between the cusps would be prevented, 

 while at the same time the segments would afford one another mutual support. 



Method. 



My object was, if possible, to fix the heart in the various stages of the cardiac cycle, 

 to harden it, and by sections and dissection to determine the position of the valves in 

 the various phases, so that an actual demonstration of the true condition might be 

 afforded. 



Eabbits were chiefly used, on account of their being of convenient size and easy to 

 procure, but many observations were also made upon the hearts of cats, dogs, sheep, and 

 men. 



The Rabbit was killed by a blow behind the head. The thorax was then rapidly 

 opened, the larger vessels being carefully avoided to prevent loss of blood, and the peri- 

 cardium was slit up. The method of procedure then varied according to the condition 

 in which it was desired to fix the heart. To imitate the third stage of ventricular systole* 

 during which the ventricle remains contracted after the expulsion of the blood, clamps 

 were applied on the large vessels and the organ was excised and plunged momentarily 

 into boiling water, the clamps being taken off at once. This procedure produced a gush 

 of blood from the great arteries and a smaller flow from the great veins, and fixed both 

 auricles and ventricles in a firmly contracted condition. 



To imitate the first stage of ventricular systole — the contraction of the ventricles 

 before blood is expelled into the arteries — is more difficult ; because when respiration 

 stops the right heart becomes engorged with blood. 



The method of procedure was to expose the heart as above described, and then to 

 ligature or clamp the great vessels, and to plunge the ventricles for a second or two into 

 boiling water or hot perchloride of mercury solution, care being taken to prevent such 

 overheating as would distort the valves and chordae. This at once caused a contraction 

 of the ventricles ; . but this was frequently accompanied by a regurgitation into the 



