INHIBITORY NERVES TO THE VASCULAR SYSTEM 85 



in the heart, are inhibitory in nature right up to their termina- 

 tions in the muscular tissue itself. The auricle is separated from 

 the sinus and left in connexion with the ventricle, the coronary 

 nerve alone connecting the ventricle and auricle with the vagus 

 nerve. The contractions of auricle and ventricle are registered 

 separately. Such a preparation remains still for a long time and 

 then contractions begin, which gradually and slowly increase in 

 rate. If the right vagus in the neck is then stimulated no altera- 

 tion of rate is caused, but a marked diminution in the strength of 

 the auricular contractions is seen as the result of the stimulation. 

 The fibres of the vagus then, which run in the coronary nerve, 

 inhibit the contractions of the auricle. Tf the vagus is stimulated 

 before the contractions begin, when the auricle is quiescent, there 

 is no visible result, but the galvanometer shows that a change of 

 potential takes place in the muscular tissue of the auricle of the 

 opposite kind to what is seen when a contraction occurs, the 

 muscle becomes more positive instead of more negative. These 

 experiments have been confirmed recently by Meek and Eyster 

 and Samojloff and are evidence that a chemical change is caused 

 in the muscle by inhibitory nerve fibres producing a change of 

 potential of an opposite kind to that produced by the action of a 

 motor nerve. 



I have considered the evidence for the existence and position 

 of the various groups of inhibitory cells for unstriped muscle be- 

 longing to the skin, gut system, and heart, and propose to take 

 now the evidence for inhibitory nerve cells and fibres for the 

 unstriped muscles of the vascular system. It is at first sight 

 strange to find that, although the existence of inhibitory nerve 

 cells is as clear and undisputed in the case of the unstriped 

 musculature already considered as the existence of motor nerve 

 cells, there is no undisputed evidence for the existence of inhibitory 

 nerve cells to the vascular unstriped musculature, although the ex- 

 istence of their motor cells is indisputable. There is a large amount 

 of evidence to show that the blood vessels of an organ may dilate 

 upon stimulation of an efferent nerve, especially if that nerve sets 

 the organ at the same time into activity, and again and again the 

 doubt arises whether the dilatation observed is really due to the 

 action of vaso-dilator nerves, or is brought about in some way in 

 consequence of the activity of the organ. We must always re- 

 member that the vascular system is to be regarded, not as a system 



