280 VEGETABLE DRUGS 



Dose.—H., gi-.i-iss, (.06-.09) ; C, gr.i-ii, (.06-.12) ; Sh. & Sw., gr. l/lS-1/12 

 (.004-.005); D., gr. 1/120-1/80 (.0005-.0008), average dose, gr. 1/100 (.0006). 



Action of Belladonna and Atrophine 



External. — Belladonna is ordinarily not absorbed from the unbroken 

 skin, but when applied to raw surfaces and mucous membranes, or, to a 

 less extent, when rubbed into the skin with camphor (linimentum bella- 

 donnse), chloroform, alcohol, etc., it depresses the sensory nerve endings 

 and produces a local anodyne action. Thus applied it also depresses the 

 peripheral motor nerve fibres, and is sometimes injected into spasmodi- 

 cally contracted muscles for relief of spasm. The vessels are said to 

 be first contracted and then dilated by the local action of the drug, and 

 the secretions of the skin are diminished. 



Internal. — Digestive Tract. — Belladonna (atropine) apparently di- 

 minishes the gastric secretion and is largely used to lessen gastric hyper- 

 acidity. In the intestines atropine prevents undue griping produced by 

 drastic cathartics through checking violent action caused by overactivity 

 of the motor nerve (vagus) endings in the small intestines. Also it 

 overcomes the intestinal contraction which forms about any irri- 

 tating body in the lumen of the gut — even gas. While tending to prevent 

 catharsis through depressing the motor (vagus) nerve endings of the 

 small gut, it does not hinder the action of drugs stimulating directly the 

 intestinal wall (arecoline) — only that of agents acting on the motor 

 nerves — as eserine. On the contrary, atropine aids catharsis in most 

 cases by: 1. relieving spastic abnormal conditions. 2. by preventing 

 spasm and griping through over-action of the vagus. 



Circulation. — Belladonna is readily absorbed into the blood, but has 

 no particular action upon this fluid within the body. Dilute solutions of 

 atropine paralyze and stop corpuscular movement in the blood withdrawn 

 from the vessels. The characteristic action of belladonna upon the cir- 

 culation consists in depression of the peripheral pneumogastric fibres in 

 the heart, with greater frequency of the pulsations. There is apparently, 

 in the mammal, no direct stimulation of the cardiac muscle. Belladonna 

 is therefore a heart stimulant, by increasing the number of its beats with- 

 out diminishing their force. Large doses sometimes give rise to primary 

 slowing of the pulse, owing to stimulation of the inhibitory apparatus. 

 Blood pressure is exalted synchronously with the increased frequency of 

 the heart, and is due to over-activity of the heart and to stimulation of 

 the spinal and medullary vasomotor centres, with constriction of blood 

 vessels, more especially of the abdomen. Dilatation of the vessels of the 

 skin occurs at the same time in poisoning, but this is insufficient to reduce 

 blood pressure. In man this is shown by flushing of the skin and a bright 

 rash on the face and neck after large doses. 



In poisoning, vascular tension is considerably lowered because of 

 paralysis of the vasomotor centres, smooth muscles (or ganglia) of the 

 vessel walls (with vascular dilation), and the heart muscle itself. 



Nervous System. — Cerebrum. — Belladonna is classed as a delirifa- 

 cient by some authorities. It stimulates the brain incoordinately, and 

 large doses produce restlessness, nervous excitement and delirium in man. 



Digitized by Microsoft® 



