AND BLOOD PRESSURE 129 



Another method of Oliver's is to place the hand, with the 

 fingers extended, in the upright position and at the level of the 

 heart's apex, taking care that the veins are not compressed by 

 clothes or the posture of the arm. He then observes the veins 

 on the back of the hand, and raising the hand until the veins just 

 collapse, measures the vertical height of the veins above the apex 

 of the heart. This measurement gives him the venous pressure in 

 millimetres of blood. The method demands that the veins should 

 be visibly distended, which may not be the case in a cool atmos- 

 phere. The venous pressure varies with warm or cold atmosphere, 

 with posture and muscular effort, pressure of the arm against the 

 body, pressure of clothes, &c., on the arm, and taking of food. 

 When the veins of the hand are contracted down with cold, we 

 cannot tell what positive pressure there is in the veins at the heart's 

 apex level by either of the above methods. The veins contract 

 down to the thread of blood which they receive when the atmos- 

 phere is cold, and dilate to hold a large volume of blood when 

 brought into play as a part of the heat-losing mechanism of the 

 body. The best demonstration of this is the network of super- 

 ficial veins which become visible in a child in a hot bath, or a 

 horse heated with work. 



If the hand be held at such a level that the veins are just 

 collapsed, and then deep and prolonged expiratory efforts or a 

 succession of coughs be made (Oliver), they will be seen to swell, 

 and this is owing to raised arterial pressure and little if at all to 

 obstructed venous outlet (T. Lewis). Prolonged inspirations, on 

 the other hand, cause the visibly swollen veins to vanish. The 

 influence of posture is seen on holding the hand and arm still 

 in the dependent position, particularly in a warm atmosphere, 

 or after exercise, or food. The veins fill under the hydrostatic 

 pressure, and the colour of the hand becomes bluish owing to the 

 lessened velocity of blood flow. A dull feeling of pressure arises 

 which is uncomfortable and causes one to move the part. Con- 

 traction of the muscles of the hand empties the blood in the 

 capillaries and veins on past the valves, and so long as the hand 

 is at work no distension or discomfort arises. If the hand be 

 kept quite still at the level of the heart's apex little congestion 

 arises. How much bodily movements further the circulation of 

 the blood can be seen by alternately placing the hand dependent, 

 and elevating it above the head, and observing how the hand 



