390 



Mr. D. T. Harris. 



stimulation of the vaso-constrictor nerves have their lumina rendered less 

 liable to extinction : this would prevent a reversal of the blood stream and 

 maintain a patent system for the onrush of blood following repeated 

 ■-contractions (fig. 4), or a prolonged contraction (fig. 5). It is difficult to 



Fig. 4. 





N. lever 



j 





f V 



♦ Stm. 



B.F. 



I; 1 I I • 1 . 1 l|lllll«HIIIII|III|||||!IIH y m ? l 1 



Fig. 5. 



imagine what function vaso-constrictors, bound up with a motor nerve, 

 might serve. Fig. 5 shows the steady diminution of the tension developed 

 in the tongue arising from the anaemia produced by its own contraction. 



4. The Vaso-dilator Nerves. 



Fig. 6, in the opinion of the writer, constitutes the most convincing single 

 piece of evidence in favour of the undoubted existence of vaso-dilator nerves. 

 Such a huge vaso-dilation in the absence of any muscular activity must be 

 independent of metabolites. The effect produced by a similar shock upon the 

 motor nerve is seen in fig. 3, where one would expect a greater production of 

 metabolites, yet vaso-dilation is absent. 



How very effective a mechanical stimulus is in evoking vaso-dilation 

 (Bayliss, 1920), by excitation of the lingual nerve, is seen in the plethysmo- 

 graphic record of the tongue in fig. 7. 



