616 TEXT-BOOK OF PHYSIOLOGY. 



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 stimulated with the induced 

 electric current, among the resulting phenomena there will be observed 

 dilatation of the pupil, retraction of the nictitating membrane in animals 

 possessing it, contraction of the blood-vessels of the skin and mucous mem- 

 brane in different parts of the head, neck, and face, contraction of the blood- 

 vessels of the salivary glands* increase of secretion from the submaxillary 

 gland, and 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, dilatation and passive 

 congestion of 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 cervical portion is not only efferent in function but that 

 it transmits both vaso-constrictor and vaeo-dilatator fibers for blood-vessels, 

 secretor fibers for the salivary and mucous glands, and fibers for the dilatator 

 muscle of the iris. The fibers composing it are pre-ganglionic medullated 

 nerve-fibers coming from the spinal cord from the first to the fourth thoracic 

 nerves. From these several sources the fibers pass by way of 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. 

 The Functions of the Thoracic Portion. The phenomena which 

 follow stimulation of this portion of the sympathetic system resemble in a 

 general way those observed in the head when the cervical portion is stimu- 

 lated, viz., contraction and at times dilatation of the blood-vessels and a 

 secretion of sweat and in some animals erection of hairs. The situation of 

 the resulting phenomena will vary in accordance with the part the subject 

 of the experiment. For an understanding of the results of experiment the 

 origin and distribution of the following nerve-branches must be kept in view : 

 (a) The cardiac nerves which take their origin in part in cells in the first 

 thoracic or stellate ganglion, and in part in cells in the inferior cervical 

 ganglion. From this origin they pass downward and forward and 

 reach the heart by way of the cardiac plexus. Stimulation of these 

 nerves gives rise to an increased frequency and an augmentation in the 

 force of the heart-beat. The pre-ganglionic fibers by which these cells 



