488 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



degenerated 1 (see Fig. 129, B). The maximum effect of stimulation is more 

 quickly reached with the vaso-constrictor than with the vaso-dilator nerves. 

 There is also a difference in the latent period, or interval between stimulation 



A 



FIG. 129. Curves obtained by enclosing the hind limb of a cat in the plethysmograph and stimu- 

 lating the peripheral end of the cut sciatic nerve (Bowditch and Warren, 1886, p. 447). The curves read 

 from right to left. In each case the vertical lines show the duration of the stimulus namely, fifteen 

 induction shocks per second during twenty seconds. Curve A shows the contraction of the vessels pro- 

 duced by the excitation of the freshly-divided nerve ; curve B, the dilatation produced by an equal 

 excitation of the nerve of the opposite side four days after section, the vaso-constrictor nerves having 

 degenerated more rapidly than the vaso-dilators. 



and response. Bowditch and Warren 2 have found the latent period of the 

 vaso-constrictor fibres in the sciatic to be about 1.5 seconds, while that of the 

 vaso-dilators is 3.5 seconds. Finally, the two sorts of nerves have been said 

 to differ in the manner in which they are distributed. The vaso-constrictor 

 nerves leave the cord as medullated fibres, enter the sympathetic chain of gan- 

 glia and end in terminal branches probably in contact with a sympathetic 

 ganglion-cell. The constrictor impulse is forwarded to the vessel by a 

 process of this cell, either directly or by means of still other sympathetic 

 ganglion-cells. The vaso-dilator fibre, on the contrary, was thought to run 

 directly from the cord to the blood-vessel ; 3 but the latest investigations make 

 it probable that all spinal vaso-motor fibres end in sympathetic ganglia. 4 



Origin and Course. The vaso-motor nerves the general properties of 

 which have just been studied are axis-cylinder processes of sympathetic gan- 

 glion-cells. They follow, for a time at least, the course of the corresponding 

 spinal nerve. According to Langley, 5 they do not differ from the pilo-motor 

 and secretory nerves except in the nature of the structure in which they termi- 

 nate. They are not interrupted by other nerve-cells on their course. The 

 action of the sympathetic vaso-motor cells is influenced by the vaso-motor 

 cells of the spinal cord and bulb. These are probably small cells situated at 

 various levels in the anterior horn and lateral gray substance. 6 Their axis- 

 cylinder processes leave the cerebro-spinal axis by the anterior roots 7 of 



1 Ostroumoff, 1876, p. 228; Bowditch and Warren, 1886, p. 444. 



2 Bowditch and Warren, 1886, p. 440. 3 Kolliker, 1894, p. 2. 

 4 Langley, 1895, p. 314. 5 Langley, 1895, p. 314. 6 Kolliker, 1894, p. 6 (reprint). 



7 Budge, 1853, p. 378 Some investigators hold that vaso-motor nerves leave the cord in the 

 posterior as well as the anterior roots. Strieker ' observed that excitation of the peripheral end 

 of the posterior roots of the sciatic nerve is followed by a rise of temperature in the hind limb. 

 This was denied by Kiihlwetter. 2 Bonuzzi 3 and Gartner 4 agreed with Strieker. Morat 5 found 



Strieker, 1877, p. 279, * Kvihlwetter, 1885, p. 40. 3 Bonuzzi, 1885, p. 473. Gartner, 1889, p. 980. 

 6 Morat, 1892, pp. 1499, 694; see also Bradford. 1889, p. 363, and Morat, 1890, p. 473. 



