ACTIOX OF ATROPINE AND PILOCARPINE. 647 



pour it out tlirougli the duct of tlie gland in the form of saliva. 

 But this process does not last long, for the bean has a second 

 action. Its stimulating power is not confined to the secreting 

 nerves of the gland, but extends also to the vaso-motor nerves 

 which regulate the calibre of the blood-vessels which supply it. 

 These vaso-motor nerves, being stimulated by the drug, cause 

 the vessels to contract to such an extent as to cut off the supply 

 of blood from the glands almost entirely. The secreting cells 

 are thus deprived of the material from which the saliva ought 

 to be formed, and thus, notwithstanding the functional activity 

 which they are exerting under the stimulus of the secreting 

 nerves, the formation of saliva very shortly comes to an end. 

 In persons who are poisoned with belladonna it has been 

 observed that the vessels of the skin were much dilated, so that 

 the skin itself was covered with a scarlet flush, notwithstanding 

 which the surface was dry. This dryness was not confined to 

 the skin, but extended to the mouth, and it was caused both in 

 the mouth and on the skin by the paralysis of the secreting 

 nerves of the salivary and sweat glands produced by the drug. 

 Calabar bean, on the contrary, causes a certain amount of sali- 

 vation and cold sweats ; and other drugs, such as pilocarpine, 

 which does not, like calabar bean, limit its own action upon the 

 secreting cells of the salivary glands by lessening their blood 

 supply, causes very profuse salivation as well as profuse sweat- 

 ing. Xow the action of pilocarpine is exerted upon the termina- 

 tions of the secreting nerves in the salivary and sweat glands, 

 and does not seem to be dependent upon any action on the 

 nerve centres. But although pilocarpine may stimulate the 

 sweat glands by acting upon the ends of the secreting nerves 

 within them, it is probable that, in ordinary circumstances, the 

 secretion is regulated, not by the conditions of the terminal 

 filaments of the secretory nerves, but by the nerve centres 

 acting on the glands through those nerves. The nerve centres 

 for the secretion of sweat lie partly in the spinal cord and 

 partly in the medulla oblongata. In this respect they resemble 

 two other important nerve centres, viz., the centre for respira- 

 tion, or respiratory centre, and the vaso-motor centre — the 

 respiratory centre, by which the respiratory muscles are inner- 



2 N 2 



