i 3 4 THE MECHANISM OF THE CIRCULATION. 



employed. The fact that both kinds of nerves exist in the common 

 nerve trunks was first demonstrated by Goltz. 1 



1. If vaso-constrictors and dilators are stimulated simultaneously, the 

 constrictor influence at first overpowers the dilator. The dilator effect, 

 however, appears as an after-result, for the vaso-dilator fibres are the 

 less easily exhausted. This result can be observed in the salivary 

 gland, while the chorda tympani and cervical sympathetic nerves are 

 excited at the same time. 2 That the vaso-constrictors and dilators are 

 antagonistic in action, is shown by an experiment of v. Anrep and 

 Cybulski, 3 who recorded the variations in volume of the tongue by the 

 plethysmograph method, and determined that the constriction of the 

 tongue, induced by stimulation of the hypoglossal nerve, could be put aside 

 by an excitation of the lingual nerve. Similarly, the vaso-dilation induced 

 by excitation of the lingual could be put aside by stimulation of the 

 hypoglossal nerve. The constrictor influence is usually by far the 

 strongest. Thus Bayliss 4 found, on asphyxiating an animal during 

 excitation of the depressor nerve, that the arterial pressure rose, and the 



A B 



Fig. 82.— Plethysmograms of hind-limb. Excitations of sciatic nerve. A, One 

 per second. B, Four per second. The tracings in this and the next figure 

 are to be read from right to left. — Bowditch and Warren. 



pressor completely overcame the depressor effect. On renewing the 

 respirations, the depressor nerve again exerted its power, and the arterial 

 tension fell once more below the mean. 



2. If the leg be cooled, excitation of the sciatic nerve evokes vaso- 

 dilatation, while if the leg be warmed it produces vaso-constriction. 5 

 Similarly, if the rabbit's ear be warm, asphyxia provokes constriction ; 

 if cold, dilatation. 



3. After separation of the vasomotor nerves from the central 

 nervous system, the vaso-constrictor fibres degenerate much more 

 rapidly than the vaso-dilator fibres ; the vaso-dilator fibres maintaining 

 their excitability for some six to ten days after division, while the vaso- 

 constrictor became inexcitable on the third or fourth day. 6 



4. While the vaso-dilator fibres are excited by single induction 

 shocks repeated at intervals of not more than 5 per sec. (Fig. 82), the 

 constrictor fibres are aroused to action most easily by a rapid tetan- 

 ising current (Fig. 83). 7 



5. If the tetanising current be strong, primary vaso-constriction 



1 Arch./, d. ges. Physiol., Bonn, 1874, Bd. ix. S. 174-197. 



2 v. Frey, Arb. a. d. physiol. Anst. zu Leipzig, 1876, S. 89-107. 



s Jahresb. ii. d. Fortschr. d. Anat. u. Physiol., Leipzig, 1884, Bd. ii. S. 52. 

 4 /mn. Physiol., Cambridge and London, 1893, vol. xiv. p. 319. 

 5 Lepine, Compt. rend. Soc. de biol., Paris, 1876, p. 26. 



Dziedziul, Jahresb. ii. d. Fortschr. d. Anat. u. Physiol., Leipzig, 1880, Bd. ii. S. 68. 

 7 Bowditch and Warren, Jouru. Physiol., Cambridge and London, 1886, vol. vii. p. 32 ; 

 Bradford, Ibid., 1889, vol. x. p. 390. 



