Page:Popular Science Monthly Volume 86.djvu/148

144 axis, while themselves controlling all organs containing unstriped muscle, secreting glands or both, e. g., the smooth muscle of the bronchi, stomach, intestines, blood vessels, genitalia, eye and all the glands of external and internal secretion. The sympathetic or visceral nervous system has also been called the "vegetative" system, because the organs under its dominion functionate involuntarily or unconsciously, as with vegetables or plants. At present, the term "vegetative system," formerly termed the autonomic system by Langley, is restricted to that part of it which originates from the sympathetic ganglia, while the antagonistic system governing involuntary muscle, which is largely made up of fibers from the vagus nerve, is now styled the "vagal autonomic."

The difference between the two autonomic nervous systems and the central (cerebro-spinal) system is that, in the former, the nerve fibers never proceed, as ordinarily, directly from the nerve center to the organ controlled, but pass, as neurons, from the gray substance to a ganglion in which they encounter a break or synapse (separating surface), on the other side of which a similar post-ganglionic neuron proceeds to the organ controlled. The synapse, a term first proposed by Sir Michael Foster, has been likened to a switch over which the nervous impulse jumps to proceed on its way. Langley, the original investigator of the autonomic systems, discovered that wherever there is a switching of the nervous impulse across a synapse; the effect can be abolished in other words the post-ganglionic fiber can be paralyzed, by painting over the exposed ganglion with nicotine solution, thus determining whether an autonomic nerve fiber passes through a ganglion without interruption or not. If, after painting the exposed ganglion with diluted 0.5 nicotine solution, or even after internal administration of the alkaloid, the effect of central excitation of the post-ganglionic fiber at the ganglion is the same as ordinarily, then there is no interruption; but if the effect is abolished under these conditions, then the pre-ganglionic fiber terminates in a synapse. Langley's nicotine effect holds good for all ganglia of the autonomic systems, whether of sympathetic or vagal origin. In other respects, however, these two systems are antagonistic, both in respect of physiological functions and response to the action of drugs. The effect of electrical stimulation of a sympathetic fiber is just the opposite of that of a vagal autonomic fiber. The sympathetic fibers check, the vagal autonomic fibers excite, the movements of the intestines; the sympathetic dilates, the vagal autonomic contracts, the pupil; the sympathetic hastens, the vagal autonomic slows, the heart. Adrenalin (epinephrin), which the Viennese clinicians assume to be the specific hormone of the sympathetic autonomic, produces, on ingestion or injection, effects similar to those produced by electrical