180 SECTIONAL ADDRESSES 



A further corroboration of this somewhat new view of the function of 

 the vasodilator reflexes comes from a study of the effect of exercise and 

 of emotion on man. It is well known that when a man takes exercise 

 on a stationary bicycle his systolic blood pressure goes up, but falls even 

 below normal the moment the exercise stops. This fall has been explained 

 by Cotton, Slade and Lewis as due to the accumulation of blood in the 

 vessels of the dilated muscles, but from what I have said in relation to the 

 diminution of the peripheral resistance in muscle, it is evident that the 

 fall is in part due to a diminution of this resistance. Now if a careful 

 comparison be made of the psychical effect of intended exercise and that 

 of exercise, it has been found by Gillespie that there is no difference. In 

 other words, the rise of arterial pressure in exercise is the result of psychical 

 changes. If exercise could be taken without psychical zest being involved, 

 we might expect the blood pressure to fall. This, indeed, has been found 

 to occur in the horse. In man, too, it has been found that if the exercise 

 is slight, although the systolic arterial pressure rises, the diastolic pressure 

 falls. This means that more blood is being pumped out of the heart per 

 beat, but that blood escapes from the arteries more rapidly than normally 

 before the next systole. In other words, from psychical causes alone there 

 is a rise of arterial pressure from an increased cardiac output per beat, 

 which can only be the result of more blood reaching the heart. In 

 emotion too it is known that the systolic pressure rather than the diastolic 

 rises. Since we have seen from the experiments of Mosso with the 

 plethysmograph, of Barcroft on the exteriorised spleen and of Florey and 

 Florey on the exteriorised colon, that generalised vasoconstriction is an 

 accompaniment of psychical effort, we must assume that the increased 

 output of the heart is in part, if not wholly, the result of the vaso- 

 constriction which calls into use the reserves of blood and thus the circu- 

 lation is maintained in spite of the greatly increased capacity of the active 

 muscles. 



I am afraid that as I have gone along you have gradually become aware 

 of the complexity and difficulty of the problem. The difficulty is en- 

 hanced by the fact that in the circulation we have so many variables, and, 

 the moment we attempt to isolate one, we are at once liable to introduce 

 abnormal conditions. 



In discussing changes which may occur in exercise, I have tried to give 

 you an idea of the circulation as a working whole. For a physiologist the 

 investigation of such questions is something interesting to do, but we must 

 remember it is these same mechanisms which the body uses and develops 

 for physical exercise which the body uses to defend itself against disease 

 and injury. It is well that we should remember the words of the late 

 A. D. Waller to this Section some years ago : 



' Physiology must be studied for its own sake, but the physiologist 

 whose immediate motive is the want to know may not deny his debt of 

 service to the community of which he forms a part and whose services he 

 enjoys. And the channel through which he can repay some part of that 

 debt lies first of all in the service he may be able to render to the practice 

 of medicine — to the knowledge and power of the physician whose immediate 

 motive is the want to help.' 



