Page:Popular Science Monthly Volume 43.djvu/392

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sal regions, and of a bundle of medullary fibers, which arise in the ventral portions of the brain and pass out from it immediately below the entrance of the ganglionic fibers. Evidently there are two roots, which, from their close juxtaposition, have been hitherto unrecognized; the ganglionic bundle is the true dorsal root, the medullary bundle the lateral root. If, now, we modify Bell's law by saying that all medullary fibers are efferent or motor, and all ganglionic fibers afferent or sensory, we can understand the double function of the facial nerves and of the other nerves resembling it—to wit, the trigeminal, glosso-pharyngeal, and vagus.

The recognition of the lateral root as distinct from, though joined with, the dorsal sensory root, removes many obscurities in the anatomy of the nervous system. We know that lateral roots are not confined to the nerves of the head, but tlioy also occur in the upper cervical nerves, and I regard it as highly probable that with the progress of research they will be found sharing in the formation of other spinal nerves. Should this expectation be fulfilled, the long-established conception of the posterior roots as purely sensory will have to be modified, although it has reigned for three quarters of a century as one of the fundamental conceptions of physiology.

The Third Discovery.—The third discovery is that neither the nerve cells nor nerve fibers are directly continuous either with other nerve cells or with the cells or structures of other tissues and organs. Every nerve cell, together with its fiber, is an entity, and is not organically continuous with anything else. It is certainly premature to affirm this discovery positively, for we can say at present only that the consensus of the best opinion, of such men, for instance, as His and Kölliker, is in favor of the conception that every nerve cell plus its nerve fiber is an isolated element. • Until recently the hypothesis was received with favor that the cells of brain and spinal cord were connected by threads of protoplasm, or, to speak more precisely, by branches of the processes of the cells; according to this hypothesis, there would be a direct protoplasmatic continuity between the different parts of the nervous system, and therefore a nerve impulse brought by a sensory fiber to the brain could be conceived as traveling along an uninterrupted pathway of living matter until it produced its final action. In many text-books of physiology there are diagrams to illustrate the theory of a continuous pathway. It is evident that if there is no such connection between nerve cells as assumed, then we must radically alter our conceptions of the process of the transmission of nerve force through the brain.

In the question before us, Camillo Golgi and his followers must lead the way. Golgi, whom the world will probably rank