248 PHYSIOLOGY. 



The coronary veins have their outflow temporarily retarded by 

 the contraction of the right auricles, an action partially contributed to 

 by the valve of Thebesius. The coronary veins empty themselves when 

 the auricles relax. 



The frequency of the mammalian heart is changed but little by the 

 quantity of blood flowing through the coronary arteries, but the quan- 

 tity is of great importance, for the force of heart. If the heart has no 

 work to do it has need of only a very small amount of blood. 



Frequency of the Heart's Action. During health the heart acts 

 so smoothly and with so little concern on our part that there is 

 required considerable self-attention before any differences are seen 

 to exist. Its action, as studied from the throbbings (pulse) that are 

 exhibited by some of the more superficial arteries, and each of which 

 corresponds to ventricular systole, is found to lie in very close sym- 

 pathy to the other great functions of the economy and is accordingly 

 influenced by them. The average number of adult beats is 72 per 

 minute. Even in health great deviation on either side of this stand- 

 ard may exist, depending upon age, sex, size, food, drink, exercise, 

 posture, etc. That age and sex exercise an influence upon the 

 frequency of the heart's movements must be remembered by the 

 clinician when making his diagnosis. From the annexed table it will 

 be noticed that just before birth the rate, as determined by the stetho- 

 scope, is very high, but gradually diminishes until very old age, when 

 there is a slight increase. Sex is very influential, the female heart 

 averaging about eight beats more per minute. 



It has been noticed that the rule seems to be that smaller animals 

 possess a greater amount of neuro-muscular activity than larger ones. 

 Among human beings this is also applicable, shorter people usually 

 having a pulse that is a trifle more rapid than taller people. Idios}^n- 

 crasies are frequently found which are at first very misleading to the 

 diagnostician. Thus, the pulse of Napoleon I often did not exceed 

 40 beats to the minute, yet he was perfectly well. After each meal 

 there is an increase of from 5 to 10 beats, while following very violent 

 exercise the figures 140 or 150 may be reached. 



During health there is found a nearly constant relation existing 

 between the number of heart-beats and of respirations. This pro- 

 portion is four heart-beats for every single respiration. Even when 

 the number is very much increased from violent exercise or any other 

 cause, the proportion still remains constant. Pathological conditions 

 usually alter this relation. Landois gives the following results : 



In male adults the pulse-rate is 72, in females 80. 



