380 VEGETABLE DRUGS 



depressing the efferent vagus endings in the bronchial 

 tubes and relaxing spasm of the smooth muscle of their 

 walls. 3. As a sedative, by depressing the afferent vagus 

 fibres and diminishing the irritation produced by secre- 

 tion, so that cough is allayed. 4. As an agent lessening; 

 secretion. 



Temperature. — Moderate doses of belladonna cause a. 

 rise of temperature, while fatal doses lessen bodily heat. 

 The first phenomenon is produced by stimulation of the 

 spinal thermogenic centres, while the latter effect follow* 

 the vasoinotor paralysis which occurs after lethal doses. 



An elevation of 2-5.4° F. has been noted in dogs after 

 full doses of atropine, while a greater fall of temperature 

 has been observed in the same animal in fatal poisoning. 

 Elevation of temperature is accompanied by increased heat 

 loss, caused by radiation from the dilated cutaneous vessels. 



Eye. — The action of belladonna upon the eye affords 

 another illustration of the depressing action of the drug 

 upon the nerve terminations. The oculomotor nerve end- 

 ings are paralyzed by belladonna, and therefore dilation of 

 the pupil ensues. 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 terminations of the sympathetic and 

 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 consists in depression of the oculomotor nerve end- 

 ings, 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. 



Digitized by Microsoft® 



