356 YEGETABLE DRUGS 



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 corpuscular movement in the; blood withdrawn .from the 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 its 

 pulsations is increased. There is also, probably, a slight 

 stimulation of the cardiac muscle, or its contained ganglia. 

 Belladonna is therefore a heart stimulant, by increa,sing 

 the number 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 stimulation of the spinal and medullary vaso- 

 motor centres, with constriction of blood vessels. 



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. — Cereh^um — 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 ia 

 succeeded by exhaustion and some depression, with stupor 

 rather 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 stim- 

 ulated. 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- 



