The autonomic nervous system is concerned with the regulation of the involuntary mechanisms of the body. It has afferent, central, and efferent nervous components, including specialized sensory areas responsive to chemical or pressure changes. Functionally, it is an elaborate system of reflexes designed to control automatically the responses of the smooth muscles, the blood vessels, the heart, and the glands of the body. The efferent nerves supplying these latter structures have been classified as “adrenergic” or “cholinergic,” according to the nature of the supposed chemical mediator released at their effector sites. Even the adrenergic efferent pathways, however, have a cholinergic component, the sympathetic preganglionic nerves, and cholinergie mechanisms have been suggested as being involved in the functioning of some central and afferent parts of the autonomic nervous system. It is obvious, therefore, that the anticholinesterase (anti-ChE) agents, by interference with these cholinergic phenomena, may produce profound and widespread changes in the function of the autonomic nervous system. All these changes will be manifested by effects produced in the organs and tissues supplied by the autonomic effector nerves. For example, general intoxication with an anti-ChE agent may produce miosis, lacrimation, salivation, tightness of the chest, respiratory distress, and cardiovascular embarrassment (see Chapters 18, 20, and 22 for details).