194 INTERNAL SECRETION 



autonomous system.* Further investigation reveals the fact, how- 

 ever, that fibres which produce entirely opposite results are not 

 necessarily derived from different sources. Indeed, it has been 

 shown that both systems frequently send nerve fibres to the same 

 organ and that the function of the fibres is apparently identical ; 

 on the other hand, nerve fibres producing completely opposite 

 results appear to proceed from the same system. 



We must assume that the complete nervous supply to a 

 vegetative organ comprises a fourfold innervation, namely : (i) 

 autonomous stimulatory ; (2) autonomous inhibitory ; (3) sym- 

 pathetic stimulatory; and (4) sympathetic inhibitory. A number 

 of instances of such fourfold innervation are already known, but 

 investigation of the subject is of so recent a date that the informa- 

 tion which is forthcoming is necessarily very incomplete. The 

 conditions under which the innervation of the various vegetative 

 organs takes place offer a wide field for inquiry in the 'future. 



The table upon pp. 192 and 193 shows all that is at present 

 known concerning the innervation of the vegetative organs. They 

 also show the relationship between the individual organic func- 

 tions and certain poisons. 



The study of the action of certain toxins has brought im- 

 portant functional characteristics to light, and has revealed func- 

 tional differences between the animal and vegetative systems on 

 the one hand, and the autonomous and sympathetic portions of 

 the vegetative system on the other. These differences are for the 

 most part fundamental and in accordance with certain laws; and 

 they depend upon the chemistry of the organs and, more particu- 

 larly, upon the chemical differentiation of the nerve endings. 



Langley showed that nicotine has an elective affinity for 

 those ganglion cells, which, throughout the vegetative system, pro- 

 duce an anatomical break in the continuity of the neuron, and in 

 which a functional change in the nature of the nervous stimulus 

 takes place. After the intravenous injection of nicotine and the 

 effect is even more marked if a diluted nicotine solution is applied 

 directly to a ganglion there is a transient stimulus, followed by 

 paralysis, of those ganglion cells in which commutation of 

 stimulus takes place. Electric stimulus produces certain effects 

 upon nerve fibres of the vegetative system, and the results of this 

 stimulus, whether applied before or behind a ganglion, are 

 identical. But the effect of nicotine is to paralyse the obstructing 

 gangtion cell and its influence is entirely confined to this cell 

 with the result, that stimulus of the pre-ganglion fibre is negative, 

 while the post-ganglion fibre responds in the ordinary way. 



* Following a system of nomenclature adopted by English physiolo- 

 gists, it is proposed to describe any action, whether a muscular contraction, 

 an increase in the cardiac function, a contraction of the vessels, or the 

 promotion of the secretion of an organ as motor effect or function (F.). 

 The prevention of function of whatever nature (muscular relaxation, cardiac 

 insufficiency, vasodilation) is termed inhibition (I.). 



