Principles of mental physiology Author:William Benjamin Carpenter Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: ferenoe, and for their transmission to the ganglionic centres; whilst the other serves for the transmission of the impressions that call forth Muscular contracti... more »on, from the ganglionic centres to the various parts of the circumference.—In most Nerve-trunks, afferent and motor fibres are bound up together; although, in the ordinary Spinal nerves of Vertebrata, these are connected by separate "roots "'with the Spinal Cord which serves as their gnnglionic centre (§ 62). But the nerves of special sense (the Olfactive, Optic, and Auditory), which proceed to those special ganglionic centres of which the aggregate constitutes the Sen- sorium, contain no motor fibres; and there are other nerves of the head in Vertebrata, which are either solely afferent or solely motor (Fig. 11). 40. The analogy just indicated between the two components of every Nervous System, and the two parts of an Electric Telegraph, —that in which change originates, and that which serves as the conductor,—holds good to this further extent; that as, for the origination of the Electric current, a certain Chemical reaction must take place between the exciting liquid and the galvanic combination of metals, so is it necessary, for the production of Nerve-force, that a reaction should take place between the Blood, on the one hand, and either the central nerve-cells, or the peripheral expansions of the nerve-fibres.- We do not know, it is true, what is the precise nature of that reaction : but we have the evidence of it in the largo supply of Blood which goes to all Organs of Sense,—i.e., to organs which are adapted for receiving sensory impressions and transmitting them to the central Sensorium ; and, yet more, in the extraordinary proportion that is transmitted to those central organs which receive those impressions, r...« less