328 THE NERVOUS SYSTEM 



The sacral autonomic supplies the lower end of the gut 

 and the organs of reproduction, with the exception of the 

 uterus. 



The sympathetic supphes (a) the gut, with its diver- 

 ticula, from the cardiac orifice of the stomach to the 

 rectum; (6) all the arterioles of the body, except those 

 of the brain and heart ; (c) the hairs and sweat glands of 

 the skin ; {d) the pupil and sahvary glands ; (e) the urino- 

 genital organs. 



3. As a general rule, to which, however, there are some 

 exceptions, an involuntary organ is supphed by nerves 

 from two sources : (a) the sympathetic ; (6) the cranial or 

 sacral autonomic. The organ is usually capable of activity 

 independently of both these nerves. The two nerves serve, 

 the one to increase its activity, the other to decrease it. 

 The cranial and sacral autonomic have the effect of exalt- 

 ing digestive and reproductive functions ; the sympathetic, 

 while it depresses these functions, adjusts the animal to 

 a condition of defence or offence. 



4. Between its exit from the central nervous system and 

 its destination the nervous impulse passes through one 

 cell-station, and one only. This rule, to which no excep- 

 tion has yet been found, is known as Langley's law. A 

 fibre which issues from the central nervous system {pre- 

 ganglionic fibre) is invariably medullated, and in the case 

 of the sympathetic is known as a white ramus commu- 

 nicans. The distal fibre with which this communicates 

 (post-ganglionic fibre) is invariably non -medullated. The 

 arborisation between the terminal filaments of the pre- 

 ganghonic fibre and the nerve-cell of the post-ganglionic 

 fibre can be identified by nicotine, which blocks conduc- 

 tion at the synapses. It takes place in one of three 

 situations : (a) in the gangha of the sympathetic (lateral) 

 chain ; (b) in the great gangha situated upon the ab- 

 dominal aorta and its branches [collateral chain), and 

 (c) peripherally in the organ itself {terminal ganglia). 



It follows from what has been said that certain fibres 

 may pass through a ganghon without interruption. The 



