Page:Popular Science Monthly Volume 26.djvu/752

732 These proceedings offer a considerable number of facts not readily classifiable under any theory now at hand.

There is present and urgent need for a clear statement of the case respecting nerve-matter and consciousness. There is equally urgent need that this statement should be reasoned upon according to the fundamental working of reason—viz., the detection of difference and similarity. It is the proper reward of modern science to have taught that reasoning is the procedure from the known to the unknown by the pathway of resemblance. This resemblance must be experimentally determined and experimentally verified. Dr. Maudsley says, most truly, in his last edition of the "Physiology and Pathology of the Mind": "It will not advance knowledge to identify phenomena of a different kind by giving them the same name; on the contrary, the progress of knowledge lies in following the specializations of development, and in defining differences by a precise use of terms." The characteristic phenomena of nerve-matter and the characteristic phenomena of consciousness should be stated and compared: if these phenomena prove different, they should be described in the light of that difference, and all conclusion as to their origin should be drawn according to that difference. Our first inquiry, then, is concerning the nervous system, as to its parts and functions.

The histological elements of the nervous system are two, the fiber and the cell. The fiber appears under two forms, the medullated and non-medullated. The medullated fiber consists of a central thread or axial band, then a soft substance called the medulla, and, inclosing these, a tubular sheath. The axial band is the essential anatomical element of the fiber. It is an albuminoid substance—that is to say, it is highly unstable in character and complex in structure. The medullary substance is transparent, homogeneous, and strongly refracting, like oil; it consists chiefly of lecithin and cerebrin. The sheath is a lime-substance. The differences in chemical composition between this axial band and its marrow-like inclosure were shown by Lister and Turner in 1859. The band becomes red by a solution of carmine, while the marrow substance is unchanged, and in turn this substance becomes opaque and brown under chromic acid, while the band remains unaltered.

The second element of nerve-matter is the cell. This, in its fully developed condition, is of irregular shape, with strongly refracting granular contents and a distinct nucleus and nucleolus. Many of the cells have one or more prolongations, and are accordingly classed as unipolar, bipolar, or multipolar. One at least of the processes of a multipolar cell is continuous with a fiber and is called the axial-cylinder process. In the cells and in the intercellular substance of central nerve-organs, albuminoid stuff is closely mingled with the other component parts of nerve-matter.

The proportion of solids to water is but twelve per cent in the