ACTION OF BELLADONNA 383 



they therefore draw back the edges of the iris and dilate the pupil. 

 The nerve terminations in the radiating fibres do not seem to be influenced 

 by atropine. The mydriatic action is exhibited, whether the drug be 

 given by the mouth or dropped directly into the eye. In the former case, 

 the drug does not act through the nervous system, but locally upon the 

 peripheral filaments of the third nerve through the medium of the blood. 

 The muscular fibres of the iris are unaffected by belladonna. The ter- 

 minations of the sympathetic and the trigeminus may be stimulated, 

 which would also produce dilation of the pupil. These latter actions are 

 not definitely determined, while it is known that the dominant effect cou'- 

 sists in depression of the oculomotor nerve endings, as before stated. 

 Paralysis of accommodation follows paralysis of the terminations of the 

 third nerve in the ciliary muscle, and therefore vision is disturbed. Intra- 

 ocular tension is increased by large and continuous dosage of belladonna, 

 and an artificial glaucoma may be thus produced. 



Elmination. — Belladonna is eliminated by the kidneys and bowels; 

 traces have been found in the milk. It is, however, chiefly oxidized in 

 the body. 



Summary. — It will be observed that belladonna, generally speaking, 

 first stimulates and then depresses the nerve centres, while it chiefly 

 paralyzes the motor nerve terminations, including the inhibitory (vagus), 

 the secretory (chorda tympani, etc.), and, to a less extent, the sensory 

 nerves. Secondary depression of the cerebrum is not so profound as 

 that of the great medullary centres, especially the respiratory centre, and 

 there is sometimes a slight and brief stimulation of the motor nerves of 

 the smooth muscles, viz., vagus, splanchnic, and possibly vasomotor nerves. 



Full medicinal doses depress the peripheral filaments of the inhibi- 

 tory and secretory nerves and the motor nerves of the unstriped muscles, 

 as well as the muscles themselves, of the viscera (allaying spasm of 

 bronchi, intestines, stomach, etc.), lessen the functional activity of the 

 voluntary motor system^ and, to a less degree, that of the afferent nerves. 

 The pulse becomes quickened because of paralysis of the peripheral vagus 

 endings and stimulation of the heart; the blood tension is augmented be- 

 cause of the increased cardiac action and stimulation of the vasomotor 

 centres; and the respiration is accelerated because of excitation of the 

 respiratory centres. The temperature is elevated owing to the circulatory 

 exaltation and stimulation of the heat-producing centres. Slight delirium 

 may be present from the exciting action of the drug upon the cerebral 

 motor centres. 



The spinal cord is unaffected by therapeutic doses. Locally ap- 

 plied belladonna is a direct paralyzant to nerves, muscles, vessels and 

 cells. 



Physiological Relations of Belladonna to Other Drugs 



In stimulating nerve centres atropine resembles both caffeine and 

 strychnine, with this difference, that caffeine excites chiefly the higher 

 psychical centres of the brain, while strychnine sensitizes the connecting 



Digitized by Microsoft® 



