176 THE BLOOD AND ITS CIRCULATION. 



paleness (white anger), is it not more reasonable, instead of 

 maintaining that a low degree of this passion is paralyzing 

 and a paroxysm exciting, to see in the first case a slight, 

 clonic excitation, causing peristaltism and hyperaamia ; and in 

 the second a violent tetanic excitation, producing permanent 

 constriction of the vessels, anaemia and extreme paleness? 



We see, by the statement of these different and, often, 

 opposing theories, that we are still far from being decided as 

 to the nature of the vaso-motor phenomena, or vasculo- 

 motors (Beclard). More just ideas, up to a certain point, have 

 been acquired on the origin and course of the vaso-motor 

 nerve fibres. 



The vaso-motor centres are placed, partly in the spinal 

 cord, but principally in the cephalic (cerebral) parts of the 

 medullary cord, for section of the cervical cord causes dilata- 

 tion of all the arteries of the body. Experiments by Ludwig, 

 Thiry, and Schiff, show that these centres are placed in 

 the protuberance and peduncles of the brain: here take 

 place the central phenomena of reflexes which, after irritation 

 of the sensitive nerves, diminish the tonicity of the vessels. 

 Injury to the cerebral peduncles causes hyperaemia, especially 

 in the abdominal viscera, and may lead to softening of the 

 gastric mucous membrane or coat (Schiff). Irritation of 

 these peduncles causes retraction of all the vessels (Budge). 

 The cerebellum appears, however, to have some share in the 

 vaso-motor operations, and the cervical cord may be the seat 

 of the vaso-motor phenomena concerned in the functions of 

 salivary secretion. 



From these vaso-motor centres originate centrifugal fibres, 

 following the spinal axis, and passing successively to the 

 arteries by the medium, of the great sympathetic nerve. 

 In this course the vaso-motor nerves follow especially 

 the antero-lateral columns : they cross each other, for, in 

 hemiplegia from a central cause the vaso-motor lesion, as 

 with other lesions of the motor tract, is observed on the 

 opposite side to that of the encephalic lesion ; this decus- 

 sation, however, as with the voluntary motor nerves, ap- 

 pears to be made suddenly at the level of the bulb, and 

 there is no other decussation of the vaso-motor nerves in 

 the remainder of the spinal axis (Brown-Sequard). Thus, 

 in spinal hemiplegia, the vaso-motor disturbances are ob- 

 served, like those of the motor tract, on the same side as 

 the medullary disease, and on the opposite side to the dis- 

 turbances affecting sensation (see page 46) : that is, the 



