38 GENERAL ACTION OF DRUGS 



(2) DEPRESSING MOTOR NERVE-TERMINATIONS. 



Curare Cocaine Lobeline. 



Conium Camphor Nicotine 



Amyl-nitrite Prussic acid and many others 



Atropine 



Uses. — Drugs influencing the peripheral motor nerve-endings are not 

 of any practical therapeutical value for this purpose (except lobeline). 



IV. — Drugs Acting on the Nerves of Special Sense. 



(A) Drugs acting on the eye. 



(1) Drugs influencing the pupil. — The mechanism controlling the 

 pupil consists of the centres for the contraction of the pupil (in the cor- 

 pora quadrigemina), the centres for the dilatation of the pupil (mid- 

 brain and lower ciliospinal), the third nerve, the cervical sympathetic 

 and the circular and radiating (latter sometimes absent) muscular fibres 

 of the iris. Drugs may act either centrally or locally on these structures. 

 The pupil is dilated by drugs (1) depressing the contracting centre (ocu- 

 lomotor), (2) the terminations of the third nerve or (3) the circular 

 fibres of the iris; and contrariwise, by (4) stimulating the dilating centre, 

 (5) the terminations of the sympathetic or (6) the radial fibres of the 

 iris ; and, finally, by a combination of these actions. 



Again, the pupil is contracted by drugs stimulating (1) the oculo- 

 motor centre, (2) the terminations of the third nerve or (3) circular 

 fibres of the iris; and by depressing (4) the dilating centre, (5) the ter- 

 minations of the sympathetic or (6) the radial fibres of the iris ; and also 

 by a combination of these actions. Drugs may act locally on the pupil 

 through the medium of the circulation as well as when dropped into the 

 eye. Furthermore, absorption and central action may occur when drugs 

 are dropped into the eye as well as when entering the blood through the 

 more ordinary channels. 



The drugs used in the treatment of the diseases of the eye are only 

 those acting locally. Drugs influencing the pupil are divided into two 

 classes: (1) those that contract the pupil (myotics) and (2) those that 

 dilate the pupil (mydriatics). 



(1) Mydriatics. 



(a) ACTING LOCALLY. 



Atropine 



Homatropine 



Hyoscyamine 



Hyoscine 



Scopolamine 



Gelsemine 



Cocaine stimulates sympathetic endings 



(b) ACTING CENTRALLY. 



Anesthetics (late in their action) 



The dilating centre is stimulated by carbonic dioxide in the blood, 

 and therefore dilatation of the pupil occurs in asphyxia ; also after irrita- 

 tion of sensory nerves, the sexual organs and digestive apparatus. 



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