738 NERVOUS SYSTEM. 



demonstrating that its section paralyzed the muscular walls of the arteries, and, farther, 

 that galvanization of the nerve in the neck caused the vessels to contract. This was the 

 discovery of the vaso-motor nerves, concerning which so much has been written within 

 the past few years, and it belongs without question to Brown-Sequard, who published 

 his observations in August, 1852. A few months later, in the same year, Bernard made 

 analogous experiments and presented the same explanation of the phenomena observed. 



The above embraces all that is important with regard to the history of experimental 

 observations upon the sympathetic. It is evident that we could know nothing of the 

 functions of this system before the time of Pourfour du Petit, when the prevailing opin- 

 ion was that the nerve originated from the encephalon, and that its influence was propa- 

 gated downward ; and writings anterior to the experiments of Bernard and of Brown- 

 Sequard present interesting suggestions and theories, but they contain little that bears 

 upon our positive knowledge. 



The important points developed by the first experiments of Bernard and of Brown- 

 Se*quard were, that the sympathetic system influences the general process of nutrition, 

 and that many of its filaments are distributed to the muscular coat of the blood-vessels. 

 Before these experiments, it had been shown that filaments from this system influenced 

 the contractions of the muscular coats of the alimentary canal. Leaving, for the present, 

 the action of the vaso-motor nerves, we shall briefly recapitulate some of the facts with 

 regard to the influence of the sympathetic upon animal heat and secretion. 



When the sympathetic is divided in the neck, the local increase in temperature is 

 always attended with a very great increase in the supply of blood to the side of the head 

 corresponding to the section. The increased temperature is due to a local exaggeration 

 of the nutritive processes, apparently dependent directly upon the hypereemia; and it is 

 not probable that there are any nerves to which the name of calorific, as distinguished 

 from vaso-motor, can justly be applied. There are numerous instances in pathology of 

 local increase in temperature attending increased supply of blood to restricted parts. In 

 a recent experiment by Bidder, after excising about half an inch of the cervical sympa- 

 thetic in a half-grown rabbit, the ear on that side, in the course of about two weeks, 

 became distinctly longer and broader than the other. 



The experiment of dividing the sympathetic in the neck, especially in rabbits, is so 

 easily performed, that the phenomena observed by Bernard and Brown-S6quard have 

 been repeatedly verified. We have often done this in class-demonstrations. A very 

 striking experiment is the following, suggested by Bernard : After dividing the sympa- 

 thetic and exhibiting the increase in the temperature and the vascularity of the ear on 

 one side in the rabbit, if both ears be cut off just above the head with a sharp knife, the 

 artery on the side on which the sympathetic has been divided will frequently send up a 

 jet of blood to the height of several feet, while, on the sound side, the jet is always 

 much less forcible, and it may not be observed at all. This experiment succeeds best in 

 large rabbits. 



It is very easy to observe the effects of dividing the sympathetic in the neck, but 

 analogous phenomena have been noted in other parts. Among the most striking of these 

 experiments are those reported by Samuel, who noted an intense hyperaemia of the 

 mucous membrane of the stomach and intestines following extirpation of the coaliac 

 plexus. ^ By comparative experiments, it was shown that this did not result from the 

 peritonitis produced by the operation. 



As regards secretion, the influence of the sympathetic is very marked. When the 

 sympathetic filaments distributed to a gland are divided, the supply of blood is very much 



reased, and an abundant flow of the secretion follows. This point we have already 



discussed in another chapter, where we have referred particularly to the experiments of 



Bernard upon the salivary glands. In some recent experiments by Peyrani, it has been 



shown that the sympathetic has a remarkable influence upon the secretion of urine. 



When the nerves are galvanized in the neck, the amount of urine and urea is increased, 



