

CHAP, iv.] THE VASCULAR MECHANISM. 307 



effects, the quickening and strengthening of the beats, seems to 

 point to its setting in action the augmentor mechanism, but it 

 also probably acts directly on the cardiac tissues. In any case the 

 effects depend largely on the dose, and if this is large the direct 

 effects become prominent, and the ultimate result is a deleterious 

 weakening. 



Any large widening of the cutaneous area, especially if accom- 

 panied by muscular labour and the incident widening of the 

 arteries of the muscles, would tend so to lower the general blood 

 pressure (unless met by a wasteful use of cardiac energy) as 

 injuriously to lessen the flow through the active digesting viscera. 

 A moderate constriction of the cutaneous vessels on the other hand, 

 by throwing more blood on the abdominal splanchnic area without 

 tasking the heart, is favourable to digestion, and is probably the 

 physiological explanation of the old saying, " If you eat till you 're 

 cold, you '11 live to be old." 



In fact during life there seems to be a continual give-and-take 

 between the blood vessels of the somatic and those of the splanchnic 

 divisions of the body : to fill the one the other is proportionately 

 emptied, and vice versa. 



173. In the following sections of this work we shall see re- 

 peated 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 sub- 

 ject. 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. 



