THE CIRCULATION OF THE BLOOD 



695 



In 1893, in the course of investigations with this nerve, I found that the 

 phenomena were not to be satisfactorily explained on this view alone, and 

 suggested (p. 317) that, both in pressor and in depressor reflexes, inhibition 

 of the one centre is associated with excitation of the opposite one. 



Ostroiimov, working with Heidenhain (1876), had already expressed the view 



C.C. 



FIG. 244. Experiment similar 

 to that of the preceding 

 figure. 



Upper curve, volume of hind leg of dog. 



Lower curve, arterial pressure. Zero, 

 23 mm. below signal. 



Signal marks stimulation of central 

 end of vagus. 



Time in ten-second intervals. 



The reflex dilatation obtained after 

 section of the vaso-constrictors in 

 the abdominal sympathetic can be 

 abolished by subsequent section of 

 the spinal cord at the second lumbar 

 nerve, by which operation the con- 

 nection of the vaso-dilators with the 

 centre is severed. 



(Bayliss, 1902, 3, Fig. 7.) 



FIG. 24o. DIAGRAM OF THE ARRANGE- 

 MENTS OF VASOMOTOR REFLEXES. 



A, Muscle cell of arteriole. 



D, Vaso-dilator nerve-fibre terminating on A, and 



inhibiting its natural tonus. 

 C, Vaso-constrictor fibre also ending in A, but 



exciting it. 

 These two kinds of fibres arise from the dilator 



centre (D.C.) and the constrictor centre (C.C.) 



respectively. 

 F, Afferent depressor fibre, dividing into two 



branches (or collaterals), one of which (-) 



inhibits the constrictor centre, while the other 



(+) excites the dilator centre. 

 R, Pressor fibre of ordinary sensory nerve, causing 



rise of arterial pressure by exciting C.C. and 



inhibiting D.C. 

 a, b, c, d, The respective synapses of these branches 



with the efferent neurones. 

 The probable intermediate neurones are, for the 



sake of simplicity, omitted. 



(Bayliss, 1908, 2, Fig. 27.) 



that the reflex dilatation in the skin vessels produced by the depressor nerve 

 is due to excitation of vaso-dilator fibres, but it does not seem to have occurred 

 to these and subsequent investigators that both excitatory and inhibitory actions 

 are concerned. After Sherrington's work on the reciprocal innervation of skeletal 

 muscle, I took up the question again (1908, 2), and showed that this mode of 

 innervation applies also to vasomotor reflexes, although, of course, the phenomena 

 are complicated by the fact that both the centres and the effectors can be excited 

 or inhibited. There are thus four cases to be considered, which must be done 



