1024 PHYSIOLOGY 



varies inversely as the blood pressure. This relation, though general, is not 

 universal. Thus the rise in blood pressure and the increased filling of the 

 heart associated with muscular exercise are attended by an increased pulse 

 rate. In the quickening of the heart, which accompanies bodily exercise, 

 another reflex mechanism comes into play, to which attention has been 

 called by Bainbridge. Any distension of the right auricle evokes a reflex 

 quickening of the pulse rate, chiefly by diminishing the vagus tone but 

 also probably to a less extent by reflex stimulation of the reflex accelerator 

 nerves. It thus seems that the heart is connected with the heart centre 

 in the medulla, governing its rate of beat, by two sets of afferent nerves, 

 which are stimulated by a rise of pressure within the cavities to which they 

 are distributed. Stimulation of the one set coming from the arterial end 

 e. g. the left ventricle, causes a reflex slowing of the heart. Stimulation of 

 the other set, which are distributed to the venous end of the heart, evokes 

 ihcreased frequency of the heart beat. Both these sets of impulses are of 

 great importance in correlating the activity of the heart and the amplitude 

 of the circulation with the metabolic needs of the body as a whole. 



THE PULSE RATE IN MAN 



The normal pulse rate in man is about 72 per minute. It is largely 

 influenced by bodily movements. It varies considerably with age. The 

 following Table represents the average pulse rate in man at different ages : 



Age in years Pulse rate per minute 



o . . i:j(> 



5 . . 88 



10-15 . . 78 



15-60 . . 68-72 



It must be remembered that marked differences in the pulse rate may be 

 found in different individuals without having any pathological significance. 

 Thus pulse rates of 30 per minute and 120 per minute have been observed in 

 men who were otherwise perfectly healthy. The pulse rate is raised by 

 warmth and diminished by cold applied to the surface of the skin. It is 

 also increased somewhat by the taking of food. The act of swallowing causes 

 a reflex quickening of the rate by inhibition of the tonic vagus action. 



