314 CIRCULATION. 



onstrated pulsation in the veins of the hand, and also in 

 the arm, foot, and leg. These movements are very slight, 

 and are generally only appreciable by some such delicate 

 means of investigation. This is a strong argument in oppo- 

 sition to the opinion of those who regard the action of the 

 heart as inoperative in the veins. In certain cases of disease, 

 Mr. King has noted very marked pulsation in the veins of 

 the back of the hand, and other vessels far removed from 

 the heart. 



Pressure of Blood in the Veins. The pressure in the 

 veins is always much less than in the arteries. It is exceed- 

 ingly variable in different parts of the venous system, and in 

 the same part at different times. As a rule, it is in inverse 

 ratio to the arterial pressure. Whatever favors the passage 

 of blood from the arteries into the capillaries has a tendency 

 to diminish the arterial pressure ; and, as it increases the 

 quantity of blood which passes into the veins, must increase 

 the venous pressure. The great capacity of the venous sys- 

 tem, its numerous anastomoses, the presence of valves which 

 may shut off a portion from the rest, are circumstances which 

 involve great variations in pressure in different vessels. It 

 has been ascertained by Yolkmann, and this has been con- 

 firmed by others, that as a rule the pressure is diminished as 

 we pass from the periphery toward the heart. In an obser- 

 vation on the calf, he found that with a pressure of about 6*5 

 inches of mercury in the carotid, the pressure in the meta- 

 tarsal vein was 1*1 inch, and but 0'36 in the jugular. 1 The 

 pressure is, of course, subject to certain variations. Muscular 

 effort has a marked influence on the force of the circulation 

 in certain veins, and, consequently, in these vessels produces 

 an elevation in the pressure. As the reduced pressure in the 

 veins is due in a measure to the great relative capacity of 

 the venous system, and the free communications between the 

 vessels, it would seem that if it were possible to reduce the 



1 MILNE-EDWARDS, Lemons sur la Physiologic, Paris, 1859, tome iv., p. 329. 



