THE CIRCULATION OF THE BLOOD 691 



the dorsal roots of the splanchnic area caused dilatation in the intestine, so that 



FIG. 238. VASOMOTOR REFLEXES. 



Upper curves in each fig., volume of intestine of cat, recorded by plethysmograph. Fall indicates arterial 



constriction. 

 Lower curves, arterial pressure in aorta. Mercury manometer. The initial normal height was 90 mm. 



mercury. Each division of the scale represents 2 mm. of mercury change of pressure. 

 Upper signal, time in ten-second intervals. 

 Lower signal, stimulation. 



1, Stimulations, three in number, of the central end of the median nerve. Rise of blood pressure, caused by 



peripheral constriction, as shown by the volume of the intestine. 



2, Stimulation of the central end of the vagus (depressor). Fall of blood pressure, caused by peripheral 



dilatation (increase of volume of the intestine). 



3, Similar to previous curve. Showing effect of more prolonged stimulation in producing permanent fall of 



blood pressure, probably owing to secondary effect of anaemia on the heart. 



the dilator fibres contained in the splanchnic nerves may not be of sympathetic 

 oricrin. 



