146 DR RUTHERFORD ON THE INFLUENCE OF THE VAGUS 



These experiments (XXXIX.-LIII. inclusive) show, — 



1st. That in rabbits division of the vagi may be followed by increased blood- 

 pressure and accelerated pulse, although the cardio- inhibitory nerves are 

 paralysed, and therefore totally inactive before the division of the nerves. 



2d. In experiments XXXIX., XLV., XLVL, the pulse was unaffected by 

 the section : in experiment XLIV. it was retarded, and, notwithstanding, the 

 blood-pressure was increased in all these cases. A rise in the blood-pressure 

 following division of vagi may therefore be quite independent of the heart. 



3d. The blood-pressure was unaffected when the vagi were divided during 

 fasting, while it rose after their section during digestion. When we remember 

 that when the vagi are divided during digestion a permanent blanching of the 

 stomach takes place (see p. 126), it is evident that the rise in pressure in the 

 experiments under consideration must be ascribed to contraction of gastric 

 vessels chiefly if not entirely. It therefore appears that the increased blood- 

 tension which frequently follows division of the vagi cannot — as has hitherto 

 been supposed — be wholly ascribed to increased action of the heart liberated 

 from its inhibitory nerves (see p. 120). Instead of depending only on one 

 factor it really depends on two. Cessation in the action, 1st, of cardio-inhibi- 

 tory ; and 2d, of vaso-inhibitory fibres of the vagi. 



4th. The evidence afforded by these experiments and those previously given 

 (see page 126), shows that during digestion inhibitory influences pass from the 

 stomach through the vagi to paralyse those vasomotor cells in the medulla 

 which preside over the gastric blood-vessels. But during fasting, when the 

 gastric blood-vessels are in a contracted state, both the vaso-inhibitory and 

 excito-vasomotor fibres of the vagi are at rest. (Were the latter in an active 

 state, a fall in the blood-pressure would follow division of the vagi during 

 fasting). It appears, therefore, that although the vaso-inhibitory fibres of the 

 vagus play an important part in dilating the gastric blood-vessels, the role 

 assigned to the gastric excito-vasomotor fibres of the vagi is as yet unknown. 

 Vasomotor nerve-cells appear, like their homologues the cells of the cardiac 

 ganglia, to be continually evolving energy. By reason of this, they would 

 constantly keep the blood-vessels in at least a semi-contracted state, were it not 

 that their power of generating energy may be controlled by inhibitory nerves. 

 These nerves appear to be brought into play by the tissues of a part when it 

 demands a greater influx of blood, but when it has no such demand, it does not 

 appear that the excito-vasomotor nerves are brought into action to increase the 

 evolution of f jrce in the vasomotor nerve-cells, but it seems that in this case the 

 tissues simply cease to excite vaso-inhibitory nerves. I am, therefore, inclined 

 to think that these excito-vasomotor nerves discharge their functions on occasions 

 much more extraordinary than those on which the vaso-inhibitory fibres operate ; 

 but what those are must be left for future research to determine. 



