NERVOUS CONTROL AFFECTING THE SECRETION OF SWEAT. 537 



fuse secretion of sweat, it is true, appears usually to be associated with 

 vascular dilatation, like the secretion of saliva after irritation of the 

 facial nerve. Indeed, the sudoriferous and the vascular nerves appear 

 to pursue almost identical paths. 



For the hind extremity, in the cat, these fibers are contained in the sciatic 

 nerve. Luchsinger was able to excite constantly renewed secretion of sweat for 

 half an hour by irritation of the peripheral stump, if the paw was constantly 

 kept dry. This nervous activity is destroyed by atropin. If a young cat, whose 

 sciatic nerve on one side has been divided, is placed in a room filled with hot air, 

 the three intact members soon sweat, but not that with the divided nerve, not 

 even when excessive hyperemia of the member is induced by ligation of the veins. 

 The sweat-fibers pass centripetally from the sciatic nerve, in the abdominal sym- 

 pathetic, in order to reach the upper lumbar and lower dorsal cord (twelfth dorsal 

 and first, second, and third lumbar roots in the cat), through the communicating 

 branches of the sympathetic and through the anterior roots. The center for the 

 secretion of sweat in the hind extremities is situated in the ganglia of the anterior 

 horns in the lower dorsal and upper lumbar portions of the spinal cord. According 

 to Langley, non-medullated sweat-fibers pass in the cat to the nerves from the 

 eleventh dorsal to the fifth lumbar, and are derived from the sixth and seventh 

 lumbar and the first and second sacral ganglia of the sympathetic. The origin 

 and course of the vasomotors are, on the whole, the same. 



This spinal center may be irritated directly (i) through marked 

 venosity of the blood; therefore through dyspneic stimulation. In 

 this category belongs probably also the sweat of the death-agony. (2) 

 Through overheated blood (45 C.) passing through the center. (3) 

 By certain poisons (see p. 536). Reflex stimulation of this center is 

 effected, though with varying result, through irritation of the crural or 

 peroneal nerve of the same side, as well as of the sciatic nerve of the op- 

 posite side. 



For the fore-paws, in the cat, the sweat-fibers pass in the ulnar and median 

 nerves. These pass from the dorsal roots between the fourth and the tenth to 

 the dorsal division of the sympathetic, and then pass downward through the 

 stellate ganglion, and thence into the nerves of the anterior limb. 



An analogous center for the anterior extremities is situated in the 

 lower half of the cervical cord. Irritation of the central stump of the 

 brachial plexus causes reflex sweating of the paw of the opposite side. 

 Under such circumstances, the hind paws also sweat at the same time. 



Pathological. Degeneration of the motor ganglia of the anterior horns of the 

 spinal cord induces loss of the secretion of sweat, together with paralysis of the 

 striated muscles of the trunk. Perspiration is increased in enfeebled as well as in 

 edematous extremities. Nephritic patients exhibit great variations in the amount 

 of water given off by the skin. Dieffenbach observed that sweating reappeared 

 in transplanted bits of skin only after the return of sensitivity. 



The sweat-fibers for the head (man, horse; snout in swine) are derived from 

 the upper dorsal sympathetic, pass through the stellate ganglion and ascend in 

 the cervical sympathetic. The observation is probably appropriate here that in 

 human beings percutaneous galvanization of the cervical sympathetic causes 

 sweating on the same side of the face and the arm, as well as the pathological 

 observation that in association with unilateral sweating of the head, neck, and 

 upper extremity, the corresponding pupil is dilated and the skin is pale. In the 

 cephalic portion of the sympathetic the sweat-fibers enter the branches of the 

 trigeminus, and this fact explains the circumstance that irritation of the infra- 

 orbital nerve excites the secretion of sweat. Some fibers, however, arise directly 

 from the trigeminal roots and the facial nerve. 



Undoubtedly, the cerebrum must also exert a direct influence either 

 upon the vasomotor nerves or upon the sweat -fibers, as is shown by the 

 sweating that attends emotional disturbances, fright, etc. 



