SOMNAMBULISM AND DREAMS 591 



Howell and others have studied the circulation by the plethysmographic 

 method during sleep. The results show that with the loss of consciousness, and 

 immediately following, there is a sharp dilatation of the blood-vessels of the 

 arm, probably chiefly of the skin, as shown by the increase in volume. The 

 vessels remain dilated until the individual begins to awaken, when there is 

 a rapid constriction with decrease of volume of the organ. 



The dilatation of the general blood-vessels draws off the supply of blood 

 from the brain, and the resulting partial anemia contributes to loss of conscious- 

 ness. The blood supply is ample for growth and repair and rest of the nervous 

 system. How efficient this rest period is for the rejuvenation of the nervous 

 tissue is indicated even by the relatively gross means, figure 356, shown in 

 the histological preparations of nerve cells. 



Somnambulism and Dreams. What we term sleep occurs often in very different 

 degrees in different parts of the nervous system; and in some parts the expression cannot 

 be used in the ordinary sense. 



The phenomena of dreams and somnambulism are examples of differing degrees of sleep 

 in different parts of the cerebro-spinal nervous system. In the former case the cerebrum 

 is still partially active; but the activity is no longer corrected by the reception, on the part 

 of the sleeping sensorium, of impressions of objects belonging to the outer world; neither 

 can the cerebrum, in this half-awake condition, act on the centers of reflex action of the vol- 

 untary muscles, so as to cause the latter to contract a fact within the painful experience 

 of all who have suffered from nightmare. 



In somnambulism the higher centers are capable of coordinating that train of reflex 

 nervous action which is necessary for progression, while the nerve center of the muscular 

 equilibrium sense (in the cerebellum?) is, presumably, fully awake; but the sensorium 

 is still asleep, and impressions made on it are not sufficiently felt to rouse the cerebrum 

 to a comparison of the difference between mere ideas or memories and sensations derived 

 from external objects. 



VI. THE SYMPATHETIC SYSTEM. 



The fact has already been emphasized that the sympathetic system of 

 nerves is an organic and constituent part of the nervous system. 



Organization and Distribution. The sympathetic system consists 

 of those collections of nerve cells or ganglia lying outside of the brain and 

 cord (exclusive of the root ganglia), and the nerve tracts connecting them 

 with one another and with the cerebro-spinal axis. Its parts that should be 

 mentioned are : i, a double chain of ganglia and fibers, which extends from the 

 cranium to the pelvis, along each side of and in front of the vertebral column, 

 and from which branches are distributed both to the cerebro-spinal system 

 and to other parts of the sympathetic system. With these may be included the 

 small ganglia in connection with those branches of the fifth cerebral nerve 

 which are distributed in the neighborhood of the. organs of special sense, 

 namely, the ophthalmic, otic, spheno-palatine, and submaxillary ganglia. 

 2, Various ganglia and plexuses of nerve fibers which give off branches to the 

 thoracic and abdominal viscera, the chief of such plexuses being the cardiac. 



