508 



PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



thus indicating that there has been an actual recession of the chest, and 

 representing graphically the condition known in clinical language as the 

 "negative impulse." 



FIG. 201. TRACING OBTAINED WITH THE CARDIOGRAPH WHEN THE BUTTON 



is PLACED AT APEX BEAT OF THE HUMAN HEART. (/Sanderson.) 



Each ascent in the curve coincides with the ventricular systole. 



To recapitulate, it may be stated that a single pulsation of the heart 

 may be divided into three phases : 1st. The auricles contract, while the 



FIG. 202. CARDIOGRAPH TRACING OBTAINED WHEN THE BUTTON is PLACED 



TO ONE SIDE OP APEX BEAT. (Sanderson.) 



The line of descent coincides with the ventricular systole. 



ventricles are relaxed, con traction and relaxation occurring synchronously 

 on both sides of the heart. 2d. The ventricles contract, while the 



- 



FIG. 203. HEART-BONES OF A Cow, NATURAL SIZE. (Mutter.) 



a, larger, b, smaller heart-bone ; c, anterior, d, posterior extremity. 



auricles are relaxed. 3d. Both auricles and ventricles are in a state of 

 relaxation, the auricles being near the end and the ventricles at the 



commencement of their diastole ; this 

 phase is termed the pause, the con- 

 dition of ventricular contraction being 

 described as systole, of relaxation as 

 diastole. The duration of a cardiac 

 revolution, consisting of diastole, sys- 

 tole, and pause, is equal to the interval 

 of time ^tween two pulsations felt in 



THE HEART-BONES. ONE-HALF THE nT1 \r nrtprv 

 NATURAL SIZE. (Milller.) > a er -> ' 



a, larger heart-bone ; b, smaller heart-bone : c, The ActlOH of the VdlveS OJ the 

 root of the aorta ; d, right coronary artery ; e, rigrht 

 semi-lunar valve ;/, central part of the mitral valve. Heart. The direction of tllC CUrreilt 



of circulating blood through the heart is rendered possible solely 

 through the integrity of the cardiac valves. These A'alves, as already 



