THE CIRCULATION, 279 



acter. It is obvious at the outset that the organ presents itself in 

 two different conditions, alternating with each other in rapid suc- 

 cession ; namely, a condition of rest and a condition of movement. 

 One of these is the condition in which it expels the blood from 

 the ventricles into the arteries ; the other is that in which the ventri- 

 cles are again filled with blood from behind. The first object of the 

 observer is to determine the time at which each one of these two con- 

 ditions presents itself, and the physical changes in the organ by which 

 it is accompanied. If the heart be touched or gently grasped by the 

 fingers, its alternations of rest and movement are felt to correspond with 

 similar variations in its consistency. At the time of rest it is compar- 

 atively soft and yielding ; at the time of its movement it becomes hard 

 and tense. If a slender silver canula be inserted, through the walls of 

 the left ventricle, into its cavity, the blood is ejected from the outer 

 extremity of the canula at the instant of the heart's tension and move- 

 ment, while its flow is suspended in the intervals of repose. 



It is evident, therefore, that the time of the heart's movement is that 

 of the ventricular systole, in which the muscular walls of the ventricles 

 close upon their contents, and propel the blood into the arterial sys- 

 tem. Like other muscles, the heart assumes, at the instant of contrac- 

 tion, a condition of rigidity, readily perceptible on placing the fingers 

 in contact with its surface. 



If the muscular fibres of the heart ran in a straight direction be- 

 tween their points of origin and insertion, its changes of form and 

 position, like those of most voluntary muscles, w^ould be compara- 

 tively simple. But they are in the form of elongated curvilinear loops, 

 which have their origin in the fibrous zones at the base of the organ, 

 and, after embracing the ventricular cavities, return to be inserted into 

 the same fibrous zones or into the chord* tendineae. As the entire 

 heart, furthermore, is attached at its base, while its body and apex are 

 movable, the united action of its fibres produces a combination of 

 simultaneous movements different from those of other muscular organs. 



In an anterior view of the dog's heart, the base of the organ, at 

 each ventricular systole, appears to approach its apex. The point of 

 the heart is at the same time protruded, tilted slightly from left to 

 right, and rotated in the same direction on its longitudinal axis. 

 The protrusion of the apex can be felt somewhat forcibly by the end 

 of the finger applied lightly to its surface, and it can also be shown by 

 the movement of a long steel needle suspended vertically on a hori- 

 zontal axis, so that its lower extremity touches the point of the heart. 

 At each cardiac systole, the upper end of the needle moves backward, 

 as its lower end is thrown forward by the protrusion of the apex. 

 At the same time, the body of the organ is increased in thickness from 

 its anterior to its posterior surface, and diminished in its transverse 

 diameter, that is, from the right to the left lateral border. All these 

 phenomena depend on the anatomical arrangement of the contracting 

 fibres. 



