352 THE HEART AND PERIPHERAL RESISTANCE. [Booic i. 



condition of the medulla itself, or indirectly by impulses reaching 

 the medulla along afferent nerves from various parts of the body,) 

 may send inhibitory impulses down the vagus, and so slacken or 

 tone down the heart-beats. 



In the following sections of this work we shall see repeated 

 instances, similar to or even more striking than the above, of the 

 management of the vascular mechanism by means of the nervous 

 system, and we therefore need dwell no longer on the subject. 



We may simply repeat that at the centre lies the cardiac 

 muscular fibre, and at the periphery the plain muscular fibre of the 

 minute artery. On these two elements the central nervous system, 

 directed by this or that impulse reaching it along afferent nerve 

 fibres, or affected directly by this or that influence, is during life 

 continually playing, now augmenting, now inhibiting, now the one, 

 now the other, and so, by help of the elasticity of the arteries and 

 the mechanism of the valves, directing the blood-flow according to 

 the needs of the body. 



