612 NERVOUS SYSTEM 



probable that they exist everywhere in connection with the terminal 

 filaments of this system of nerves. 



General Properties of the Sympathetic Ganglia and Nerves. The 

 sympathetic ganglia and nerves possess a dull sensibility, which is 

 particularly marked in the ganglia. That the nerves contain afferent 

 fibres is shown by certain reflex phenomena. 



Stimulation of the sympathetic produces muscular movements, but 

 these are confined usually to non-striated muscular fibres, to which 

 these nerves are largely distributed. The muscular movements do not 

 immediately follow stimulation of the nerves, but there is a long latent 

 period. The muscular contraction, also, persists for a time and the 

 subsequent relaxation is slow. The properties of the vasomotor nerves 

 will be considered separately. 



The sympathetic ganglia are connected with the motor and sensory 

 divisions of the cerebro-spinal system. Some of the ganglia and nerve- 

 plexuses are directly dependent for their action on the cerebro-spinal 

 system, while others are capable, at least for a time, of independent 

 action. Among the latter, are the ganglia of the heart, the intestinal 

 plexuses, the plexuses of the uterus and Fallopian tubes, of the ureters 

 and of the bloodvessels. 



Direct Experiments on the Sympathetic. The experiments of Pour- 

 four du Petit (1712-1725) were the first to give any positive information 

 regarding the action of the sympathetic system ; and these observa- 

 tions may be taken as the starting-point of a definite knowledge of the 

 physiology of the sympathetic, although they showed only the influence 

 of the cervical portion on the eye. In 1816 Dupuy removed the supe- 

 rior cervical ganglia in horses, with the effect of producing injection of 

 the conjunctiva, elevation of temperature in the ear and an abundant 

 secretion of sweat on one side of the head and neck. These experiments 

 showed that the sympathetic has an important influence on nutrition, 

 calorification and secretion. In 1851 Bernard divided the sympathetic 

 in the neck on one side in rabbits and noted on the corresponding side 

 of the head and the ear increased vascularity and an elevation in tem- 

 perature of 7 to 11 Fahr. (4 to 6 C). This condition of increased 

 heat and vascularity continues for several months after division of the 

 nerve. In 1852 Brown-Sequard repeated these experiments and attrib- 

 uted the elevation of temperature directly to an increase in the supply 

 of blood to the parts affected. He made an important advance in the 

 history of the sympathetic by demonstrating that its section paralyzed 

 the muscular coat of the arteries, and further, that faradization of the 

 nerve in the neck caused the vessels to contract. This was the discov- 

 ery of the vasomotor nerves, and it belongs without question to Brown- 



