VASOMOTOR CENTRES. 137 



pressure in the cerebral arteries provokes a fall of aortic tension ; con- 

 versely, a fall of pressure in the cerebral arteries provokes a rise. In 

 other words, cerebral anaemia, however produced, excites the centre, and 

 increases vascular tone, while cerebral hyperemia decreases vascular 

 tone. 



Besides the bulbar centre, there are other subsidiary centres in the 

 spinal cord. (The word centre is here used to signify nothing more 

 than a portion of the central nervous system, wherein afferent impulses 

 are changed into efferent impulses.) The existence of these spinal 

 centres was first established by Goltz. After destruction of the whole 

 brain of a frog, the vascular tone is not abolished completely. It is 

 abolished after destruction of the spinal cord. 1 



In mammals the same statement holds true. If, after section of the 

 spinal cord in the lower dorsal region, a dog be maintained alive, reflex 

 vascular dilatation causing erection of the penis can be evoked, and, 

 while the vessels of the lower limbs are at first dilated, they return 

 with the lapse of time to a state of tone. The temperature of the lower 

 limbs, at first much raised, returns gradually to the same as that of the 

 fore-limbs. On destruction of the lumbar cord, the temperature in the 

 hind-limbs once more rises, for the vessels again dilate. 2 After section 

 of the spinal cord in the mid-dorsal region, evidence of reflex vasomotor 

 effects can be obtained. Thus, on sensory excitation of one leg, con- 

 striction of the blood vessels in the other limb has been observed. 3 



An asphyxial rise of arterial pressure is sometimes witnessed after 

 section of the spinal cord. This rise is not obtained if the cord be 

 destroyed. 4 



Other observations showing the existence of subsidiary vasomotor 

 mechanisms in the spinal cord are (1) that, after division of the spinal 

 cord in the upper cervical region, section of the splanchnic nerves 

 causes a further depression of arterial tension, and (2) excitation of the 

 central end of one sciatic nerve causes a considerable rise of tension. 



A certain amount of evidence as to the path of the vasomotor fibres 

 down the spinal cord has been brought forward. By studying the 

 results of hemisection of the cord, it has been determined that these 

 fibres for the most part follow a direct but partly a crossed pathway. 

 If the cord be completely divided in the cervical region, and be hemi- 

 sected in the mid-dorsal region, then, on faradising the cervical cord, 

 both kidneys shrink in volume, but the kidney on the side of the hemi- 

 section contracts less than that on the other side. 5 



After section of the posterior columns and grey matter of the cord, 

 Dittmar 6 obtained the usual pressor effect which follows excitation of 

 the central end of the sciatic. We must conclude, then, that the tracts 

 pass in the antero-lateral columns. 



Local vasomotor tone. — Even after complete separation of the 

 vascular areas from the central nervous system, recovery of tone in the 

 vessels eventually takes place. Thus, when Goltz and Ewald removed 

 the lower part of the spinal cord of a dog for the length of 80 mm. or 



1 Firchow's Archiv, 1864, Bd. xxix. S. 11. 



2 Goltz, Arch./, d. rjcs. Physiol., Bonn, 1874, Bd. viii. S. 82. 



3 Vulpian, " Lecons sur l'appareil vaso-moteur," Paris, 1875. tome i. p. 292. 



4 Kowalewsky and Adaniiik, Centralbl. f. d. mcd. Wissensch., Berlin, 1868, S. 582; 

 Konowand Stenbeck, Skandin. Arch. f. Physiol., Leipzig, 1889, Bd. i. S. 407. 



5 Nicolaides, Arch. f. Physiol., Leipzig, 1892, S. 29. 



6 Dittmar, Bcr.d. k. Sachs. Gcscllsch. d. Wissensch., math.-phys. CI.., Leipzig, 1873, S. 455. 



