282 



Dr. Herbert Davies on the Areas of the 



[Mar. 17, 



rior venae cavae enter the auricle, therefore, slowly, and with small force, 

 but with an amount of velocity and momentum exactly adapted to and suf- 

 ficient for the expansion of the right ventricle. It cannot be for one mo- 

 ment maintained that the right is weaker than the left heart in proportion 

 to the work to be done by the respective sides, for each organ is exactly 

 adapted to the task which it has to perform, and the perfection of the me- 

 chanism is as manifest in one as in the other side of the heart. The right 

 side is undoubtedly exposed to sudden and great variations in the amount 

 of blood-pressure to which it is from time to time subjected ; but there 

 can be no reason for believing that provision has not been made for such 

 variations within due limits. In fact daily experience shows us how the 

 right side will maintain its vigour unimpaired, although severely and often 

 tried by the alterations in the blood-pressure resulting from rapid walking, 

 running, pulling at the oar, and the usual athletic exercises. The slowness 

 of the current which returns to the right side, the large area of the tri- 

 cuspid orifice, and the comparatively long period of time during which the 

 ventricle is open to receive its contents, evidently confirm the view that 

 the right ventricle offers but little resistance to the incoming current, and 

 that a stream of small velocity and energy is amply sufficient to fill 

 and complete the expansion of that chamber. The force which is exerted 

 by the contraction of the auricle is small, and in operation for a short 

 period of time to of a minute), and is chiefly of use, I believe, in 

 completing the closure of the tricuspid valve in the manner described by 

 Baumgartner, Valentin, and Halford. It must be also borne in mind that 

 the particles of the blood-stream which have entered the tricuspid orifice 

 in a direction nearly at right angles to the axis of the pulmonary artery 

 must, when the ventricle has become filled, change their direction of motion 

 to find their way in systole out of the ventricle. At the end, therefore, 

 of the diastole I imagine that the whole of the contents of the ventricle 

 is at rest (momentarily, but not less really so), and ready to take up a 

 new movement in a course nearly at right angles to its line of entrance 

 from the auricle. If this view, which has escaped the attention of phy- 

 siologists, be correct, we observe an additional reason for the blood which 

 enters the ventricle possessing an amount of velocity and energy just 

 sufficient, and no more, to complete the dilatation of the chamber, and 

 having performed its task, to assume for a moment an attitude of re- 

 pose before the contraction of the ventricle sends it forth in a different 

 direction. All force in the human body is economized, the means is strictly 

 adapted to the end : the left ventricle puts forth power sufficient to carry 

 the blood through the systemic capillaries to the right side of the heart ; 

 the blood enters the right auricle with an amount of pressure sufficient, 

 with the aid of the auricular contraction, to fill the ventricle, and should 

 any excess of momentum exist, it is probably annihilated by the incoming 

 current meeting the dense interlacement of the fibres of the columnse carneee 

 which form such prominent parts of the interior of both ventricles. It is 



