Chap, xiii.] CIEGULATION. 219 



important roots. It is therefore very natural that lesions of 

 the nervous centres should react on the vaso-motory nei-ves, and 

 that diverse excitations should be able to transmit themselves 

 indirectly to those nerves, by reflecting themselves on the nervous 

 centres, that is, by reflex action. 



In truth, a lesion of the cerebral peduncles and of the optical 

 layers determines a dilatation of the abdominal capillaiies, 

 especially of those of the liver and of the stomach. The elec- 

 trisation of the marrow on the level of the first dorsal vertebrae 

 acts exactly as the direct electrisation of the cervical and sympa- 

 thetic cord acts. It provokes the contraction of the vessels of 

 the head, the lowering of the temperature, the dilatation of the 

 ocular pupil, and so on. The electrisation of the spinal marrow 

 at its origin, the rachidian bulb, determines the constriction of 

 all the vessels of the body (Bezold-Ludwig, etc.).' On the 

 contrary, puncturing, chemical agents cause a general dilatation 

 of the arterioles. It is for this reason that CI. Bernard, by 

 puncturing the roof of the fourth cerebral ventricle, was able to 

 occasion saccharine diabetes, and so on. By practising from 

 below to above hemisections and total sections of the spinal 

 marrow, M. SchifE was led to consider the rachidian bulb as the 

 general centre of all the vaso-motory nerves of the body. 



As the vaso-motoiy nerves have their excitatory centre in the 

 bulb and the marrow, or at least have very intimate bonds with 

 those regions, it is very natural that they should be very 

 susceptible of undergoing reflex actions ; and in efiect all exci- 

 tations of the central end of a sectionised nerve reacts on the 

 vaso-motory nerves, generally by determining vascular contrac- 

 tions. Analogous effects are moreover produced incessantly, 

 normally, and without the slightest vivisection, in every verte- 

 brated organism. All sensitive excitation a little strong, having 

 its point of departure either from the cutaneous surface o'r from 

 a mucous surface, or from one of the organs of the senses, can 

 react on the capillary circulation. All the world knows that 

 1 Vulpian, loc. cit., pp. 210, 218, 220, 221. 



