CIRCULATION 293 



by loss of control over the muscles, so that the individual falls 

 to the ground. It may be induced by any sudden lowering 

 of the arterial blood pressure, whether due to decreased inflow 

 of blood or to decreased peripheral resistance. 



Decreased inflow may be caused by ; (a) Cardiac inhibition 

 brought about reflexly (1) by strong stimulation of ingoing 

 nerves, and more especially of the nerves of the abdomen ; (2) 

 by strong stimulation of the upper brain neurons accompanied 

 by changes in the consciousness of the nature of emotions; (6) 

 Failure of the heart to pump blood from veins to arteries against 

 the force of gravity, as when the erect position is suddenly 

 assumed by people with weak hearts. 



Decreased resistance to outflow through sudden dilatation of 

 arterioles may result from changes in the upper brain neurons, 

 accompanied by emotional states and also in digestive dis- 

 turbances. 



However induced, the anaemic state of the brain leads to a 

 stimulation of the cardiac inhibitory centre and the condition is 

 thus accentuated. The cerebral anaemia is accompanied by 

 pallor of the face. 



The treatment consists in depressing the head to allow the 

 force of gravity to act in filling the central vessels and in 

 giving diffusible stimuli to increase the action of the heart. 



THE TIME TAKEN BY THE CIRCULATION 



This was first determined by injecting ferrocyanide of potas- 

 sium into the proximal end of a cut vein, and finding how long 

 it took to appear in the blood flowing from the distal end. 

 From observation in the horse, dog, and rabbit, it appears that 

 the time corresponds to about twenty- seven beats of the heart. 



Stewart has investigated the rate of flow through different 

 organs by injecting salt solution into the artery, and by 

 detecting its appearance in the vein by the change in the 

 electric conductivity of the contents of the vessel. 



