416 



VETERINARY PHYSIOLOGY 



for the first few beats, and the ventricles may thus become 

 distended (fig. 179), but with this distension and the resulting 

 elongation of the muscular fibres of the heart the force of 

 contraction is increased (p. 224), and the heart performs the 

 increased work. In the healthy animal this dilatation 



Fig. 180. — To show the effect of increasing the venous filling of the heart 

 recorded as in fig. ITS. The upstrokes are systolic. Note the 

 enormous increase of the diastolic filling with the very marked 

 increase in the sj-stolic contraction leading to an increased output of 

 blood. (Stabling.) 



is temporary, but, in conditions of debility, over-distension 

 beyond the physiological limit may be produced, and 

 permanent distension may result. Next time a strain is 

 put upon the heart the distension may be still further 

 increased, and heart-failure may occur. 



The muscle of the heart thus acts as we have 

 seen skeletal muscle to act within physiological limits, 



