162 STUDIES IN ADVANCED PHYSIOLOGY. 



whenever the heart beats. From the fact that the activity 

 of the heart was so evident, and the further fact that the 

 final evidence of death was usually considered to be the 

 stopping of the heart, the heart received an undue import- 

 ance, traces of which till remain with us to this day in 

 many words derived from the word " heart,'' which we use 

 to express courage, emotions, vitality, inner-life, and so on. 

 The finest qualities of persons we sometimes still designate 

 as the " heart" of the man, when, of course, from a scien- 

 tific standpoint the heart has long been shown to be nothing 

 more than a big muscular pump. 



1. The rate of beat. The most easily determined 

 thing about the heart beat is its rate. This is in middle 

 adult life about seventy-two per minute. It is much higher 

 in the foetus, which just before birth reaches 140. From 

 this it gradually sinks through childhood until about the 

 twenty-first year, when the average rate of seventy-two is 

 reached. The rate is a few beats slower in men than in 

 women. L,arge persons usually have a slightly lower rate 

 than small persons. The actual rate, however, in anybody 

 is subject to great variation. These variations may be owing 

 to temperature, muscular exercise, strong emotions, or be 

 consequences of fevers or administered drugs. 



2. The events occurring in a single heart beat. Although 

 the time occurring between two successive heart beats is 

 normally less than a second, by means of proper apparatus 

 the individual events which occur in a heart beat may be 

 easily demonstrated. L,et us imagine the condition of the 

 heart at the very instant after a beat is over. L,et us suppose 

 that auricles and ventricles are empty, and the muscular sub- 

 stance of the heart is thoroughly relaxed. In this condition 

 the blood is entering the auricles, and as. the auriculo-ventric- 

 ular valves are open the blood at once falls through them into 

 the ventricles. The continued influx of the blood through 

 the auricles, gradually fills the ventricles and floats up the 

 auriculo-ventricular valves. Soon the point is reached 



