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A TEXTBOOK OF PHYSIOLOGY 



"4. It may further be observed in fishes and the colder-blooded 

 animals, such as frogs, serpents, etc., that the heart, when it moves, 

 becomes of a paler colour; when quiescent, of a deeper red colour. 



" There is also to be noticed in the heart a certain obscure un- 

 dulation and lateral inclination in the direction of the axis of the 

 right ventricle, as if twisting itself slightly in performing its work." 



Analyzing the movements of the chambers of the heart, Harvey 

 determined that : 



[ " First of all the auricle contracts, and in the course of its contrac- 

 tion forces the blood (which it contains in ample quantity as the head 

 of the veins, the storehouse, and cistern of the blood) into the ventricle, 

 which being filled, the heart raises itself straightway, makes all its 



i ( 



' ( L 



ft f9 p 



Fie. 32. SERIAL PHOTOGRAPHS OF THE PERFUSED HEART OF THE FROG, FROM A 

 CINEMATOGRAPH FILM; FIFTEEN IMAGES PER SECOND. (G. R. Mines.) 



fibres tense, contracts the ventricles, and performs a beat, by which 

 beat it immediately sends the blood supplied to it by the auricle into 

 the arteries." 



A cinematograph record of the movements of a frog's heart is 

 seen in Fig. 52. 



Movements of the Heart. The movements of the heart consist of 

 a period of contraction, which is called the systole, and a period of 

 relaxation, the diastole. The two auricles contract at the same time, 

 fallowed by the synchronous contraction of the ventricles. Finally, 

 there is a period when the whole heart is in a state of relaxation. 

 This sequence of events is known as the cardiac cycle. Taking 

 seventy-five as the average number of heart-beats per minute, each 

 cardiac cycle will occupy 0-8 second. 



