158 TEXT-BOOK OF PHYSIOLOGY 



Modifications of the Nerve Mechanism for Secretion of Saliva, 

 caused by the Physiologic Action of Drugs. The functions of different 

 portions of the nerve mechanism for salivary secretion may be made 

 apparent by an analysis of the effects that follow the administration of 

 physiologic or slightly toxic doses of the alkaloids of various drugs. The 

 effects can be shown to be due to a depression or stimulation of the 

 normal activity of one or more portions of the mechanism. As a result 

 the secretion may be decreased or increased in volume. The following 

 examples will illustrate the action of alkaloids in general. 



Nicotin. When nicotin in sufficiently large doses is given to an animal 

 hypodermatically, the secretion of saliva after a variable period of time ceases 

 and the mouth becomes dry. If the chorda tympani nerve, i.e., the pre- 

 ganglionic portion, be then stimulated with induced electric currents the 

 usual phenomenon, viz., a free flow of saliva, fails to occur. If, however, 

 the nerve branches emerging from the submaxillary ganglion, i.e., the post- 

 ganglionic portion, be stimulated with electric currents, the saliva will be 

 discharged as usual. The inference is that the receptor substance at the 

 peripheral terminations of the preganglionic chorda fibers is depressed so 

 that the nerve impulses discharged by the central mechanism fail to reach, 

 and therefore to stimulate, the submaxillary ganglion cells. The infer- 

 ence as to the seat of action of nicotin is supported by the fact that paint- 

 ing the surface of the superior cervical sympathetic ganglion with nicotin 

 will impair the conductivity of the terminal branches of the preganglionic 

 fibers emerging from the cord so that stimulation of these fibers fails to 

 produce beyond the ganglion the usual secretor effects. It is probable that 

 nicotin has a similar action on the peripheral terminations of Jacobson's 

 nerve which arborize around the nerve cells of the otic ganglion. 



Atropin. Atropin in doses of i milligram also causes a complete cessa- 

 tion in the flow of saliva and consequently an extreme dryness of the mouth. 

 After the occurrence of this condition neither stimulation of the pre-ganglionic 

 chorda tympani fibers nor of the post-ganglionic fibers, will cause the glands to 

 secrete. But as stimulation of the sympathetic nerve in the cervical region 

 will excite a secretion the inference is that the atropin exerts a depressing 

 effect on the conductivity of the receptor in contact with the gland cells 

 thus interfering with the transmission of nerve impulses, rather than on the 

 gland cells themselves. The same holds true for the nerve terminations in the 

 post-ganglionic fibers distributed to the parotid gland. The action of atropin 

 is not limited, however, to the nerve terminations in connection with salivary 

 glands but extends to the nerve terminations in connection with many other 

 glands in the alimentary canal and skin. Even though the dose of atropin 

 be large, 10 to 15 milligrams for a dog, its action is confined to the terminal 

 nerve-fibers in connection with the gland cells, for when the chorda tympani 

 is stimulated the blood-vessels around the gland dilate as usual, a fact which 

 indicates that the submaxillary ganglion gives off fibers of a vaso-dilatator as 

 well as a secretor character. Unless the dose of atropin be largely increased, 

 e.g., 100 milligrams, it fails to depress the conductivity of the terminals of 

 the sympathetic nerve-fibers. 



Pilocarpin. Pilocarpin in small doses, from 2 to 5 milligrams, hypo- 

 dermatically causes in the cat a free flow of saliva which may amount to half 

 a liter or more in the course of several hours. In human beings its effect on 



