THE AUTONOMIC NERVOUS SYSTEM 897 



of the gastrointestinal muscles and of the salivary glands and to close 

 the sphincters of the lower tract. These systems of fibers also act in an 

 antagonistic way on the heart, bladder, and interocular muscles. The 

 bulbar outflow through the vagus inhibits the action of the heart, through 

 the third nerve constricts the sphincter pupillae and probably inhibits 

 the radial fibers of the iris. The sacral outflow through the nervous eri- 

 gens causes contraction of the bladder musculature and inhibition of 

 its sphincters. In each of these cases the thoracico-lumbar outflow acts 

 on these muscles in the opposite sense. 



A large group of smooth muscles are innervated only through the 

 thoracico-lumbar outflow. Some of these, i. e., the pilo-motor muscles 

 and the muscles of the sweat glands, receive so far as we know only ex- 

 citor fibers from this system. Others receive both excitor and inhibitor 

 fibers from this system, so that an antagonism exists in the action of 

 different neurons from the same outflow. This fact has been discovered 

 by the use of a drug, ergotoxine, which prevents the excitor fibers from 

 acting upon the muscles but does not impair the action of the inhibitor 

 fibers. After the application of ergotoxine to these organs the stimula- 

 tion of their nerves results in an inhibition of the muscles rather than 

 the normal excitation. Inhibitory fibers are found in the thoracico-lum- 

 bar supply to the cutaneous blood vessels of the bucco-facial region and of 

 the kidney and their activity results in a vasodilatation in these re- 

 gions. The smooth muscles of the uterus also receive inhibitory fibers 

 from the thoracico-lumbar system, and in the virgin uterus these may 

 dominate the activity of the organ, so that its muscles relax upon stimu- 

 lation of their nerves. In the pregnant uterus, on the other hand, the 

 constrictor fibers in these nerves predominate and a contraction follows 

 their excitation. Further details of the organization of the Autonomic 

 system may be obtained from the Monograph by Gaskell. 17 



The Function of the Autonomic Nervous System 



When we examine the contribution which the autonomic nervous 

 system makes to the organization of bodily activity, we are struck by 

 .the fact that these nerves regulate the activity of a group of organs and 

 tissues which possess a high degree of autonomy, so that their various 

 functions can be carried out quite successfully when they are completely 

 isolated from the central nervous system. The heart is perhaps the most 

 complex organ under autonomic control, yet not only will isolated strips 

 of this organ contract in the rhythmic fashion characteristic of the heart's 

 activity but the entire organ will beat in a perfectly coordinated way 

 when freed from nervous control. The tonic contraction of the arter- 

 ioles, essential to the maintenance of blood pressure, is only temporarily 

 deranged by the destruction of their nerves. The musculature of the 



