262 PRACTICAL PHYSIOLOGY. [LIII. 



by forceps, so as to break the physiological continuity but not the physical, 

 both parts remaining connected with each other. In a pulsating heart, all 

 pulsates except the apex. It the bulbus aortae be compressed so as to raise 

 the pressure within the apex, the apex also beats. 



8. Movements of the Heart. Expose the heart of a freshly 

 pithed frog as directed in Lesson LIL, or better still, destroy only 

 the brain and then curarise the frog. Observe 



(a.) That the auricles contract synchronously and force their 

 blood into the ventricle, which, from being pale and flaccid, becomes 

 red, turgid, and distended with blood. 



(/>.) That immediately thereafter the ventricle suddenly contracts, 

 and forces the blood into the bulbus aortae, at the same time becom- 

 ing pale, while its apex is tilted forwards and upwards. As the 

 auricles continue to fill during the systole of the ventricle, on 

 superficial observation it might seem as if the blood were driven to 

 and fro between the auricles and ventricle, but careful observation 

 will soon satisfy one that this is not the case. Observe very care- 

 fully how the position of the auriculo-ventricular groove varies 

 during the several phases of cardiac activity. 



(c.) The slight contraction of the bulbus aortae immediately 

 following the ventricular systole. 



(d.) The diastolic phase or pause when the whole heart is at rest 

 before tiie auricles begin to contract. Ligature the fraenum and 

 divide it, gently raise up the ventricle by the ligature attached 

 to the fraenum, and observe the sinus venosus. 



(e.) The peristaltic wave, or wave of contraction, begins at the 

 upper end of the vena cava inferior and sinus venosus ; it extends 

 to the auricles, which contract, then comes the ventricular systole 

 and that of the bulbus aortae, and finally the pause ; when the whole 

 sequence of events begins again with the systole of the sinus. 



(/'.) Before the ventricular systole is complete the sinus is full, 

 while the auricles are filling. 



All this is easier to describe than to observe, and it requires 

 patient and intelligent observation to assure oneself of the succes- 

 sion of events. 



LESSON LIII. 



GRAPHIC RECORD OP THE PROG'S HEART- 

 BEATEFFECT OF TEMPERATURE. 



1. Graphic Record of the Frog's Heart (Direct registration 

 with lever). 



(a.) Destroy the brain of a frog ; curarise it. Expose the heart, 



