VASCULAR REFLEXES. 



855 



section, produces a fall of general arterial pressure. This depressor action is 

 probably a reaction upon the abdominal viscera. 



The fact that no obvious difference to the degree of fall of blood pressure is 

 made by varying the position of a transection in the cervical region, led Strieker l 

 to exclude that region from the distribution of his spinal vaso-constrictor centres. 

 The further fall of arterial pressure, caused by cutting the splanchnics after 

 cervical transection, indicates that the upper thoracic region also contains 

 vaso-constrictor centres. Bradford and Dean 2 demonstrated outflow of vaso- 

 constrictor nerves to the lungs in the upper thoracic roots, and Bayliss and 

 Bradford 3 demonstrated vaso-constrictor fibres to the brachial limb, leaving 

 by the fourth to the ninth thoracic roots. This, together with the well- 

 known upper thoracic origin of the cervical sympathetic, 4 proves, in con- 

 junction with the fact that the spinal cells of the sympathetic lie at the same 

 segmental level as the exit of their fibres from the cord, 5 the existence 

 of various spinal vasomotor mechanisms throughout the upper thoracic 

 region of the cord. Yulpian's and Kabierski's 6 above-mentioned results 

 placed similar centres in the lower thoracic region, a location confirmed 

 by Bradford's identification of the roots containing vaso-constrictors to 

 the kidney, and Bayliss and Bradford's determination of those supplying 

 the vessels of the hind-limb. The outflow of vaso-constrictors agrees, as 

 pointed out by Gaskell, 7 with the region of white rami communicantes and 

 of preponderance of small myelinate fibres in the ventral root cells. The 

 details concerning this vascular nerve supply do not belong to this portion 

 of the book; excerpts are given here only as indicating the location of 

 spinal centres that control the calibre of blood vessels and are capable of being 

 influenced reflexly. The spinal vasomotor centres not only control smaller areas 

 than does the bulbar centre, but are probably less accessible or excitable than it. 

 The rise in arterial pressure which accompanies asphyxia fails altegether or 

 occurs later after cervical transection than when the bulbar centre remains in 

 connection with the cord. 8 In the latter case the rise begins in 5 to 20 seconds, 

 and reaches its maximum 15 to 40 seconds later. After spinal transection, the 

 rise does not set in until 80 to 130 seconds after respiratory movement has 

 ceased, and does not reach its full height until 100 to 120 seconds later. The 

 reaction of the isolated spinal centres seems therefore an altogether slower 

 process than the bulbar. Probably the ordinary reflex reactions, in response 

 to excitations of different nerves, etc., play chiefly through the bulbar centre. 

 The most remarkable afferent nerve, in regard to effect on arterial pressure, 

 is the depressor, and this, a branch of the vagus, passes probably direct 

 to the bulbar centre. The afferent path for spinal nerves must suffer interrup- 

 tion in the shape of synapses somewhere in the cord en route to the bulbar 

 centre, for certainly the long dorsal-column direct path does not subserve 

 vasomotor reflex action. Excitation of the whole sciatic trunk central to its 

 section does not, with the dorsal columns of the cord alone intact, evoke any 

 change in blood pressure. The path seems to ascend in the lateral part of the 

 ventro-lateral column. 9 The path descending from the bulbar centre to 



1 Med. Jahrb., Wien, 1878, S. 21 ; ibid., 1886, S. 6. 



2 Journ. PhysioL, Cambridge and London, 1894, vol. xvi. p. 34; Proc. Roy. Soc. 

 London, 1889, vol. xlv. p. 369. 



3 Journ. PhysioL, Cambridge and London, 1894, vol. xvi. p. 10. 



4 See especially, J. N. Langley's paper, Phil. Trans., London, 1892, with full litera- 

 ture to that date. 



5 Sherrington, Journ. PhysioL, Cambridge and London, vol. xiii., "Proc. Physiol. 

 Soc.," Feb. 1892. 



6 Arch. f. d. ges. PhysioL, Bonn, 1877, Bd. xvi. S. 527. 



7 Journ. PhysioL, Cambridge and London, 1885, vol. vii. p. 1. 



8 Kowalewsky and Adam itk, Centralbl.f. d. med. Wissensch., Berlin, 1868, S. 582; Lucli- 

 singer, Arch. f. d. ges. PhysioL, Bonn, 1878, Bd. xvi. S. 518 ; Konovv and Stenbeck, 

 Skandin. Arch. f. PhysioL, Leipzig, 1889, Bd. i. S. 407. 



9 Dittmar, Arb. a. d. physiol. Anst. zu Leipzig, 1870, S. 18 ; 1873, S. 449, 



