654 



SPECIAL PHYSIOLOGY. 



When the heart of a cold-blooded animal is removed, irritation of 

 any part of it is propagated to the rest, and rhythmic contractions 

 are set up ; but if the heart be partially divided, the effects of the irri- 

 tation may be still conducted along muscular parts, but not along 

 the tendinous structures. In the entire heart, when removed, the au- 

 ricular contractions always begin at the sinus ; this fact, and also the 

 successive actions of the auricles and ventricles, justify the comparison 

 of these movements to the progressive peristaltic motions of the 

 oesophagus and intestines. When a ligature is applied around the 

 entrance of the venae cavse into the right auricle, the auricles and ven- 

 tricles remain for a time distended, but the sinus continues to contract. 



The frequency of the beats of the heart, as indicated by the impulse 

 against the left side, and by the pulse, averages, in a healthy adult, 

 about 70 in a minute ; but in the male, it is below, and in the female, 

 above that number. The frequency of the heart's beats, and therefore 

 of the pulse, is modified, however, by many circumstances. It is 

 affected by the stature, being slower in tall, and quicker in short per- 

 sons. The influence of sex just indicated may possibly be due to the 

 accompanying difference in stature ; the difference in the sexes ranges 

 from 10 to 14 per minute. Age has a still more remarkable effect. 

 Thus the pulse is quicker before birth than after. In infancy it is 

 very rapid, and it gradually diminishes in frequency as life advances. 

 It is said, however, to be somewhat slower in infants under six months 

 of age, than after that period, and also to become quicker again in 

 extreme old age : 



Frequency of the Pulse at Different Periods of Life. 



Periods of Life. No. of Beats per Minute. 



Before birth, . 150 



At birth, . . 140 to 130 



year, 



First 



Second 



Third " 



Seventh " 



Fourteenth " 



Adult life, 



Old age (above 70), 



130 u 115 

 115 " 100 



100 " 



90 " 

 85 " 



75 " 

 80 " 



90 



85 

 80 

 65 



75 



Temperament and idiosyncrasy modify the number of the heart's 

 beats, which are fewer in phlegmatic, and quicker in sanguine and 

 nervous persons. The heart beats more slowly in sleep, and more 

 quickly during excited states of the mind or body ; the depressing 

 passions lower the number of its beats, or even arrest its movements 

 altogether. Disease sometimes, as in fever and inflammation, increases 

 the frequency of the heart's action, or, as in compression of the brain 

 and in apoplexy, diminishes it. Loss of blood, when gradual and 

 moderate, diminishes the frequency of the' heart's beats ; whilst sudden 

 or excessive hemorrhage increases them. The effect of taking food, 

 is to accelerate the heart's action, animal food producing a more im- 

 mediate effect, and vegetable food a more lasting one : warm food acts 

 more quickly than cold. The effect of alcoholic and other stimulants 



