190 Prof. J. N. Langley. On Nerve Endings and on [May 24, 



recognised that poisons act upon cells apart from nerve endings, the 

 discussion on the action of adrenalin did not for a time raise the general 

 questions we are considering here. 



Taking the facts so far as they are now ascertained,* it may be regarded 

 as certain that the numerous effects produced by adrenalin are no whit 

 impaired, and probably, indeed, are increased by degeneration of the 

 sympathetic nerves which supply the structures on which it acts. On 

 the assumption that the degeneration of the nerve endings is accompanied 

 by degeneration of the nerve -fibres, this is clear evidence that adrenalin 

 stimulates by acting directly on unstriated muscle and gland cells. 



The assumption is based on the fact that the nerve-fibres, on section, 

 degenerate Tip to the peripheral plexus (or network). There is no obvious 

 reason why the degeneration should not proceed throughout. Some cells, 

 it is true, occur in close connection with the peripheral plexus, but it is 

 practically certain that these are connective tissue cells. A few experiments 

 have been made by Fletcherf on the nerve plexus in the retractor penis of 

 the 'hedgehog. In these he found that the nerve plexus did not stain with 

 methylene blue after degenerative section of the nerves supplying the 

 muscle. 



But there are difficulties in accepting the conclusion that adrenalin does 

 not act on nerve endings which are not met with or are met with to a much 

 less extent in dealing with the effect of nicotine and curari upon striated 

 muscle and nerve cells. The difficulties depend upon the apparently specific 

 relation of adrenalin to the sympathetic system. The broad facts with 

 regard to this relation are as follows : — 



Certain parts of the body are innervated by two systems of nerves, viz., 

 by the sympathetic system and by either the cranial autonomic or the 

 sacral autonomic system. It was pointed out by myselfj that the 

 stimulating effects produced by adrenalin are in all cases (with the doubtful 

 exception of the pupil in the dog)§ like those produced by stimulating the 

 sympathetic, and not like those produced by stimulating either of the other 

 systems. 



The sympathetic nerves cause contraction of nearly all the arteries of the 

 body, but the contraction varies in ease of production and in intensity ; 



* Of. Lewandowsky, 'Arch. f. (Anat. u.) Physiol.,' 1899, p. 360 ; LaDgley, 'Journ. of 

 Physiol.,' vol. 27, p. 237, 1901 ; Brodie and Dixon, ibid., vol. 30, p. 500, 1904 ; Elliott, 

 ibid., vol. 33, p. 401, 1905 ; Langley, ibid., vol. 33, p. 376, 1905. 



t Fletcher (' Proc. Physiol. Soc.,' p. xxxvi, 1897), ' Journ. of Physiol.,' vol. 22. 



% Langley, 'Journ. of Physiol.,' vol. 27, p. 237, 1901. 



§ The contraction of the pupil caused by adrenalin has been shown by Elliott (op. cit. 

 supra) to be due to central stimulation. 



