274 PHYSIOLOGY. 



entire, the heart-beats start at the venous end of the auricle and is 

 conducted to the ventricle. 



If the ventricle is stimulated by an induction shock so as to give 

 an extra beat out of the sequence, it will remain in diastole until the 

 next impulse from the auricles shoots it off and thus picks up the 

 regular sequence of heart-beat. The refractory period of the heart 

 makes it irresponsive to all other stimuli and gives the heart a rest. 



Nutrition of the Heart. In the study of the nutrition of the 

 heart, perfusion is usually employed. Ludwig and Wild, in 1846, were 

 the first to perfuse an isolated heart of a warm-blooded animal. 

 Newell Martin used the heart with the pulmonary circulation attached 

 and perfused through the jugular. Langendorff perfused through the 



Fig. 87- Refractory Period of Heart-muscle of Frog, with Com- 

 pensatory Pause. 



Shock applied at A is effective, causing an extra-contraction followed by a 

 compensatory pause, at B stimulation is ineffective. 



aorta of a completely isolated heart. The pressure of the fluid per- 

 fused closed the aortic valves, entered the coronary arteries and passed 

 out through the open right auricle. By this method the heart beats 

 for several hours. Langendorff also perfected an apparatus, which is 

 usually employed for the perfusion of the mammalian heart. Von 

 Cyon was the first to perfuse the frog's heart. 



Rabbits' serum delayed the stopping of a beating heart, whilst 

 hearts supplied with normal saline ceased to beat sooner than hearts 

 left empty. 



In the blood are found certain salts which are necessary to keep 

 the frog's ventricle pulsating. 



Merunowicz, in 1875, first discovered in Ludwig's laboratory that 

 an aqueous extract of the ash of blood had the power to keep the 

 frog's heart beating normally for hours. 



