THE SYMPATHETIC NERVE SYSTEM. 567 



eric, connects the spinal cord proper -with the muscle ; in the latter 

 system there are two, the spino-ganglionic and the ganglio-peripheric. 

 ^^^rom the distribution of the post-ganglionic fibers it may be in- 

 ferred that the activities of the vascular and visceral muscles, either 

 in the way of augmentation or inhibition, the activities of the muscles 

 of the hair- follicles, and of the epithelium of glands, are called forth 

 by the ganglia in consequence of the arrival of nerve impulses coming 

 from the spinal cord through the pre-ganglionic fiber>^Experimental 

 observations show this to be true. The extent to which these different 

 modes of activity manifest themselves in one or more regions of the 

 body will depend to some extent on the portion of the sympathetic 

 system subjected to experimental procedures. 



The Functions of the Cervical Portion. If the sympathetic 

 cord central to the superior cervical ganglion be^sthnulated with the 

 induced electric current, among the resulting pnenomenaThere will be 

 observed dilatation of the pupil, retraction of the nictitating mem- 

 brane in animals possessing it, contraction of the blood-vessels of 

 the skin and mucous membrane in different parts of the head and 

 face, contraction of the blood-vessels of the salivary glands, increase 

 of secretion from the submaxillary gland, the perspiratory and 

 mucous glands, erection of hairs in different localities of the head and 

 neck, and in the dog dilatation of the blood-vessels of the lips, gums, 

 and hard palate. If the cervical cord be divided, opposite effects 

 will be observed : viz., contraction of the pupil, dilatationTnd passive 

 congestion oT the blood-vessels, a rise in temperature, and a loss of 

 the power of erecting hairs. Stimulation of the peripheral end causes 

 a disappearance of the latter and a reappearance of the former 

 phenomena. These facts indicate that the_ceryical .portion is efferent 

 in function. The fibers composing it are medullated. nerve-nbers 

 derived from the thoracic or dorsal nerves from the first to the seventh. 

 From the several sources the fibers pass via the white rami into the 

 vertebral chain, and thence without interruption to the superior 

 cervical ganglion, in and around the cells of which their end-tufts 

 arborize in their characteristic manner. 



That the superior cervical ganglion is the cell station between the 

 spinal cord and the peripheral organs is shown by the fact discovered 

 and applied by Langley that the intravenous injection of nicotin or 

 the local application of it to the ganglion itself , impairs the conductivity 

 of the terminals of pre-ganglionic fibers, after which their stimulation 

 has no effect on the ganglion cells, though the latter retain their 

 activity, as shown on direct stimulation. Of the nerve-centers in the 

 spinal cord which through pre-ganglionic fibers influence peripheral 

 structures, some appear to be in a state of constant activity: e. g., 

 the vaso-constrictor centers and the pupillo-dilatator centers. In how 

 far this action is automatic or autochthonic, or reflex, is uncertain. 



