1 90 INTERNAL SECRETION 



THE VEGETATIVE NERVOUS SYSTEM. 



It has been the custom hitherto upon anatomical and func- 

 tional grounds, to divide the entire nervous apparatus into two 

 great systems, namely, the cerebro-spinal or animal system, and 

 the sympathetic or vegetative system. The first, by means of 

 efferent nerve fibres, supplies impulses to the voluntary, striated 

 muscles, and, by means of afferent nerves, receives communications 

 from the organs of sense. The second controls all the involuntary 

 functions; it innervates the unstriated muscular tissue throughout 

 the body, as well as the secretory glands and the striated muscle 

 of the heart ; and it also controls certain striated muscle cells at 

 the beginning and the end of the intestinal tract and in the external 

 genitals. 



From the results of descriptive anatomy it has long been 

 known that the two systems are not entirely distinct, and this is 

 confirmed by experiment. The sympathetic system is not in- 

 dependent, but is connected by means of numerous rami communi- 

 cantes with both the brain and the spinal cord. The essential 

 difference between the two systems lies in the fact, that communi- 

 cation between a striated muscle and its nervous centre is effected 

 by means of a single neuron, composed of a ganglion cell, a 

 peripheral nerve-fibre, and the terminal expansion of the latter ; 

 while in the case of the vegetative system, ganglia are interspersed 

 along the entire length of the nerve, from its source of origin 

 in the brain or cord to the organ where it ultimately terminates. 

 This arrangement is carried out, in the first place, by the ganglia 

 of the prevertebral chains, and, later, by ganglia of the second 

 and third order. These ganglia possess a special physiological 

 significance, for they represent breaks in the continuity of the 

 neuron, each ganglion cell with its nerve fibre marking the 

 commencement of a second neuron. Thus the vegetative system 

 is anatomically characterized by the presence of pre-ganglion and 

 post-ganglion fibres. That this distinction has a functional sig- 

 nificance, in other w^ords, that a change in the nature of the 

 stimulus takes place in the ganglion cells, is shown by the fact 

 that stimulation of the pre-ganglion nerve fibres before and after 

 inhibition of the ganglia (as the result of anaemia or of the action 

 of nicotine, w ? hich has a specific paralysing influence upon these 

 ganglion cells) produces entirely different effects. 



The English physiologist, Gaskell, has further drawn atten- 

 tion to the fact that, though all the anterior roots of the spinal 

 nerves supply motor nerves to the voluntary muscles, the efferent 

 fibres supplying the vegetative organs (which Gaskell calls the 

 ' visceral nervous system ") do not leave the cord in an unbroken 

 series, but are divided into three groups, separated from one 

 another by the nerve roots of the plexus of the anterior and pos- 



