In one or more of four different places, drugs that affect the autonomic nervous system may exert their actions. These places are, first, the nuclei of origin of the autonomic nerves within the central nervous system; second, the outlying ganglions located on the course of the autonomic pathways; third, the terminations of the autonomic nerves in the structures that are thus innervated, and, last, the carotid sinus. The actual nerve fibers themselves appear to be peculiarly resistant to the action of drugs.
The pharmacology of the autonomic nervous system involves some of the best and most definitely known of all drug phenomena, as well as some of the most obscure. The autonomic nervous system penetrates every nook and corner of the human body; its reaction to drugs is of interest from every angle of the practice of medicine. There is an old saying that providence exercises a special watchfulness over