204 STIMULANTS TO PERIPHERAL NERVES 



Action. Eserine or physostigmine stimulates the secretory 

 nerve endings of glands and of smooth and striated muscles. It, 

 therefore, antagonizes the action of atropine upon secretions, the eye, 

 and upon smooth muscle. It also antagonizes the action of curare on 

 striated muscle. Eserine does not affect sensory nerve endings. 



External and Local Action. There is no action except when 

 applied to the eye. 



Digestive System. Eserine stimulates the nerve endings in 

 the muscles of the bowels and probably the muscle itself and pro- 

 duces severe peristalsis. It also stimulates the. glands and "increases 

 the secretion of saliva, gastric juice, and intestinal secretions, but is 

 not used as a stimulant to secretions because by constricting the 

 arterioles and cutting off the blood supply, the secretion is limited. 

 The peristalsis is not a regular one, but consists of a fixed tetanic ring 

 (spasm) which causes griping. 



Nervous System. The higher cerebral centers are not affected, 

 since consciousness remains to the end. The vital medullary centers 

 are first stimulated, then depressed. The reflexes are depressed, and 

 in poisoning there may be ascending paralysis beginning in the 

 extremities. 



Respiratory System. Small doses may stimulate the respira- 

 tions, but they are not usually affected. Larger doses depress the 

 respiratory center, stimulate the endings of the pulmonary vagi and 

 constrict the caliber of the bronchial tubes to a dangerous extent 

 (dyspnea). The breathing is retarded with, large doses, the effect 

 being more marked upon this system than upon the circulation. 

 Death is usually due to paralysis of the respiratory center. 



Eye. When applied locally or given internally physostigmine 

 contracts the pupils, causes spasm of accommodation and lowers intra- 

 ocular tension. These actions are mainly due to the stiinulation of 

 the ocular motor endings in the iris and ciliary muscle and stimulation 

 of the muscles themselves. The effects of eserine can be counteracted 

 by atropine and vice versa; but the latter requires large doses and is 

 not so easily accomplished. 



Circulation. Small therapeutic doses do not affect the circiila- 

 tion. Moderate doses slow and strengthen the heart probably by 

 direct action on the cardiac muscle. Although the effect of the drug 

 on the heart has not been well worked out, it appears that the 

 heart is depressed under large or toxic doses. Moderate doses pro- 

 duce a marked increase in blood pressure on account of constriction of 

 the arteries from direct stimulation of the arterial muscles and 

 partly by driving the blood from the splanchnic area by constricting 

 the intestines. In toxic doses the rise in blood pressure is soon fol- 

 lowed by a fall dxie to paralysis of the vasomotor center and weak 

 heart. The heart is finally stopped in diastole. 



Secretions. All secretions, especially the sweat, tears, saliva. 



