692 



PRINCIPLES OF GENERAL PHYSIOLOGY 



The relation of these anlidromic impulses, as I called them on Lingley's 

 suggestion, to herpes has been indicated above (page 290). Affections of the 

 Gasserian ganglion may also be mentioned. 



It is found in some cases that a nerve, which ordinarily causes vaso-constriction, 

 may, after certain drugs such as ergotoxine (see the paper by Dale, 1906), produce 

 dilatation in the same region. The obvious explanation is that usually given, 

 namely, that the nerve contains both kinds of fibres, and that the constrictors 

 are paralysed by the drug. Some effects of this kind have been discussed above, 



Fi<;. 239. EXCITATION OF VASO- 

 CONSTRICTORS IN PRKSSOR REFLEX. 



Upper curve, volume of hind leg of cat. 



Lower curve, arterial pressure. Zero. 20 

 nun. below time signal. 



The vaso-dilator supply was cut oft by 

 previous section of the spinal cord in 

 the middle of the lumbar region ; that 

 is, on the cranial side of the outflow of 

 these nerves. 



The central end of the median nerve 

 (pressor) was stimulated at the time 

 indicated by the upper signal. 



(Bayliss, 1908, 2, Fig. 5.) 



.."i-.-'V , , 



1.1 '"> . >'' I ,',! 



'' ' " ''' (,.. 



FK;. 240. INHIBITION 



OF VASO- DILATOR 

 TONE IN PRESSOR 

 REFLEX. 



t"p)>er curve, arterial pres- 

 sure. Zero, 30 mm. below 

 time signal. 



Lower curve, volume of 

 external ear of rabbit. 



Yasoconstrictor supply cut 

 off by section of the 

 sympathetic nerve in the 

 neck. 



A rise of blood prt-ssun- 

 occurs when the central 

 end of the median nerve 

 is stimulated. This is 

 accompanied by diminu- 

 tion in volume of the 

 ear, although the only 

 vasomotor nerves left 

 were dilators. 



Further details will In- 

 found in the paper given 

 below. 



(Bayliss, 1908, 2, 

 Fig. 6.) 



and it was pointed out that the possibility of the effect of the constrictor fibres 

 being reversed by the drug has not yet been definitely excluded. 



Vasomotor Reflexes, General peripheral constriction or dilatation can be 

 produced reflexly, with rise or fall of arterial pressure. While nearly all sensory 

 nerves produce a rise of arterial pressure, there is a particular nerve, the depressor, 

 which always normally causes a fall. 



The depressor nerves were discovered by Cyon and Ludwig (1866), who found 

 that, in the rabbit, there is a branch of the vagus which proceeds to the heart and 

 consists of afferent fibres from this organ. When the central end of this nerve 

 is stimulated, with the main trunk of the vagus intact, a slowing of the heart 

 beat is caused, accompanied by a fall of blood pressure. That the fall of blood 



