FUNCTIONS OF THE AUTONOMIC SYSTEM 965 



Action of Nicotin and Adrenalin on the Autonomic System. 

 The action of nicotin upon the sympathetic ganglion cells, or the 

 link between them and the preganglionic fibres, which has been 

 taken advantage of in tracing the course of the autonomic fibres, 

 has already been described (p. 180). The special relation of adrena- 

 lin or epinephrin to the sympathetic, although not to the rest of the 

 autonomic system, has also been alluded to (p. 638). 



Functions of the Autonomic System. The functions of the auto- 

 nomic nerves are sufficiently denned by the enumeration of the 

 peripheral organs with which they are connected. It is obvious 

 that they preside over functions for the most part withdrawn from 

 the control of the will, the so-called vegetative functions, like the 

 heart-beat, the tone of the bloodvessels, the movements of the 

 alimentary canal and of the uterus, the erection of the hairs, and 

 the secretion of sweat. It is no doubt advantageous that these 

 functions should be withdrawn from voluntary control, and this 

 withdrawal is, we may assume, secured either by the absence of 

 anatomical connections between the regions of the cortex connected 

 with voluntary movements and the ganglion cells in the cerebro- 

 spinal axis from which the preganglionic fibres arise, or by the 

 existence of a high threshold of resistance in such paths as exist. 

 There is no anatomical or physiological reason why autonomic 

 fibres should not carry impulses which would elicit voluntary move- 

 ments were such impulses once shunted on to an autonomic path, 

 and certain autonomic fibres do innervate structures which are 

 under voluntary control e.g., the fibres to the ciliary muscle of 

 the eye and those to the urinary bladder. The power of voluntarily 

 accelerating the heart possessed by some individuals (p. 170) is 

 a further instance showing that the general rule is broken by ex- 

 ceptions. 



