AND BLOOD PRESSURE 



143 



taking time to fill up again, and that there are wider channels 

 connecting the arteries and veins through which the pressure is 

 transmitted to the veins. The existence of such wide channels is 

 recognised by histologists. Inspection of the hand and foot when 

 kept still, and held first in the dependent, and then in the horizontal 

 position, when held in the dependent position and before and after 

 contracting the muscles of the part (e.g. clenching the hand), teach 

 the enormous importance of movement in maintaining the circula- 

 tion of the blood. 1 Muscular exercise, by increasing the combustion 

 of food stuffs, and by 

 furthering the circula- 

 tion of the blood, and 

 so elimination of tissue 

 waste, is the greatest 

 source of vigorous bodily 

 and mental health. 



Standing erect and 

 with a leg relaxed the 

 arterial and venous pres- 

 sures in this leg become 

 higher than those in the 

 arm by the column of 

 blood separating the two 

 points of measurement. 



FIG. 17. Arterial pressure recorded in carotid 

 and in femoral artery, eacli artery in turn being 

 placed in the axis of rotation of the animal holder. 

 H, horizontal ; F, D, vertical feet-down posture. 

 The difference between the pressures in this posture 

 was equal to the column of blood separating the 

 two arteries. Note increased action of respiratory 

 pump. 



In students hanging head downwards by their feet, M. Flack and 

 the writer found the arterial pressure in the arm little altered from 

 the normal taken in the horizontal posture. Thus horizontal, 

 brachial 126, post-tibial artery 126 ; standing, 140 and 204 ; head 

 down, 116 and 42. The pressure in the circle of Willis was about 

 20 mm. less than in the brachial in the standing, and about 

 10 mm. more in the head-down posture. Now the column of 

 blood above the point of observation is then in the six foot man 

 almost equal to the normal arterial pressure taken in the hori- 

 zontal position. The heart by lessened output and the vaso-motor 

 mechanism by increased dilatation can compensate for this hydro- 

 static pressure, and it is clear that the heart and brain are so pro- 

 tected from a greatly increased arterial pressure. In the standing 



1 Butchers say it is easy to bleed all the tissues of an ox if it is pole-axed after 

 being driven off the road into the yard, but difficult if it has lain down for some 

 hours. 



