330 CIRCULATION. 



blood from the thorax into the external jugular, and distinct 

 pulsations, synchronous with the movements of respiration, 

 may he produced in this way. 



In some forms of cardiac disease affecting the right side, 

 a pulsation, synchronous with the heart's action, has also 

 been noticed. This is always confined to the jugular, and 

 must not be connected with the slight pulsations which 

 sometimes occur in the veins of the extremities. It is due to 

 a regurgitant impulse from the right side of the heart ; and 

 generally, to the action of the right ventricle, propagated into 

 the veins on account of pathological insufficiency of the tri- 

 cuspid valves. Two distinct pulsations accompanying each 

 act of the heart have been occasionally observed: one im- 

 mediately preceding, and the other coinciding with, the ven- 

 tricular systole. In a case of this kind, post-mortem examin- 

 ation revealed contraction of the right auriculo-ventricular 

 orifice, as well as insufficiency of the tricuspid valves. 1 The 

 relation of the pulsation of the jugular to the action of the 

 heart showed that the first impulse was produced by the con- 

 traction of the right auricle, and the second by the contrac- 

 tion of the right ventricle. 



It is evident that there are various other circumstances 

 which may impede the venous circulation. Accidental 

 compression may temporarily arrest the flow in any par- 

 ticular vein. When the whole volume of blood is materi- 

 ally increased, as after a full meal, with copious ingestion of 

 liquids, the additional quantity of blood accumulates chiefly 

 in the venous system, and .proportionately diminishes the ra- 

 pidity of the venous circulation. 



The force of gravity also has an important influence. It 

 is much more difficult for the blood to mount from below up 

 to the heart, than to flow downwards from the head and 

 neck. The action of this is seen if comparison be made be- 

 tween the circulation in the arm elevated above the head 

 and hanging by the side. In the one case the veins are read 



1 FLINT, Diseases of the Heart, Philadelphia, 1859, p. 147. 



