ACTION AND SOUNDS OF THE HEART. 227 



24 were collected. Herbst* has calculated that there is usually 

 about ten lbs. of blood in free circulation in the human body. 

 It may, therefore, be admitted with some certainty, that the cir- 

 culation of the entire mass of floating blood may take place in 

 from one to two minutes. 



— The frequency of the heart's action diminishes gradually from 

 the commencement to the end of life, thus :f 



In the embryo, the number of beats in a minute is 150 



Just after birth, ... - 130 to 140 



During the first year, - - - 115 to 130 



During the second year, - - - 100 to 115 



During the third year, - - 90 to 100 



About the seventh year, - - - 85 to 90 



About the fourteenth year, - - 80 to 85 



In the middle period of life, - - 70 to 75 



In old age, - - - - 50 to 65 



— In persons of sanguine temperament the heart beats some- 

 what more frequently than in those of the phlegmatic, and in 

 the female sex more frequently than in the male. The number 

 of pulsations in the minute varies very much in different animals ; 

 it is as low as 40 in the horse. 



— Tiie contraction (systole) of the heart is its only active state ; 

 its dilatation (diastole) is effected passively during the moment 

 of repose when the fibres are relaxed, by the blood which is 

 poured into its cavities from the contiguous veins. Dupuy, a 

 distinguished veterinary surgeon of Alfort, found, on intro- 

 ducing his hand into the abdomen of a living horse, that the 

 vena cava ascendens became turgid during the systole of the 

 heart ; and flaccid during the diastole, in consequence of the 

 blood rushing from the veins into the cavities of the heart. 

 The apex of the heart is closely in contact with the ribs, from 

 which it is separated only by the pericardium. The body of 

 the heart is also near the inner surface of the ribs and sternum, 

 for there is nothing intervening beside the pericardium but a 



* Herbst, De Sang. Quant, etc. Goettingen, 1822. 



f Mailer's Physiology, (Bennet's translation,) p. 171, vol. i. 



