376 VEGETABLE DKUGS 



the splanchnic nerve endings, the latter by direct depressant 

 action upon the unstriated muscle of the intestinal wall. 



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 wi^ drawn from the 

 vessels. The characteristic action of belladonna upon the 

 circulation consists in depression of the peripheral pneumo- 

 gastric fibres in the heart, so that the frequency of the pulsa- 

 tions is increased.* There is also, probably, a slight stimu- 

 lation of the cardiac muscle, or its contained ganglia. Bella- 

 donna is therefore a heart stimulant, by increasing the num- 

 ber of its beats without 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 cardiac stimulation and also to stimula- 

 tion of the spinal and medullary vasomotor centres, with con- 

 striction of blood vessels of the abdomen, f 



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'. — Cerehrum. — ^^Belladonna is classed as 

 a delirifacient by some authorities, — notably Wood. It stim- 

 ulates the brain incoordinately, and large doses produce 

 restlessness, nervous excitement and delirium in man, and 

 occasionally delirium in the lower animals. Stimulation is 

 succeeded by exhaustion and some depression, with stupor 

 j'ather than coma. 



Spinal Cord. — Belladonna appears to exert a double 

 ■action (stimulant and depressant) upon the spinal cord. 

 The spinal vasomotor and respiratory centres are stimulated. 

 Large doses cause complete loss of motion and reflex 

 action in the frog, lasting for several days, and followed 

 by reflex excitability and convulsions. Poisoning in 

 mammals is exhibited by less paralyzant action accom- 



* Occasionally the heart is slowed by belladonna. Perhaps by pri- 

 mary stimulation of the peripheral vagi. 



t Dilatation of the vessels of the skin occurs at the same time 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. 



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