Page:Popular Science Monthly Volume 66.djvu/166

162 logical action may be due to chemical structure and the configuration of the molecule, who can say? One's thoughts naturally turn to the living muscle plasma and the chemical changes that follow or accompany the advent of rigor mortis; to the circulating blood and lymph, and the transformations that occur when these fluids are withdrawn from the protecting influence of the endothelial lining of the living vessels; to the axis cylinder of the nerve fibers and the changes that occur when the fibers are severed from their connection with the ganglionic cells. These, and many other suggestions arise, all calling for a further study of the chemical constitution and stereochemical configuration of the molecules involved, since in the knowledge thus gained may be found the solution of many physiological processes now shrouded in mystery.

The reference just made to nerve fibers and ganglionic cells suggests another problem in physiological chemistry, solution of which has been long deferred, viz., the exact chemical nature of nerve tissue, and the character of the changes involved in the passage of a stimulus or nervous impulse through a nerve to its ending in the muscle or secreting cell. Further, what is the real purpose of the complex myelin surrounding the axis cylinder of medullated nerves, and the corresponding substance imbedded in the gray matter of the brain and cord? These are problems that have long waited solution, and yet they are vital to any clear understanding of the nutritive or other changes that take place in nerve tissue, either in rest or in activity. Nerve tissue is strikingly peculiar in its large content of phosphorized bodies of the lecithin type, cerebrosides and cholesterins. These substances, complex in nature and of large molecular structure, are all alike in having the physical properties of fats. Further, lecithin and the cerebrosides all contain fatty acid radicles in large amount, and in addition lecithin contains the radicle of glycero-phosphoric acid. Moreover, the cerebrosides contain a carbohydrate group yielding galactose on decomposition, so it is plain to see that the bodies which give character to the myelin material are highly nutritive substances with high calorific power. These facts might readily be taken as indicating that the function of the myelin is to nourish the more important axis cylinder, to furnish the necessary pabulum for growth and repair, as well as to meet the daily demand for energy-yielding material.

While we may speculate, however, as to the part these peculiar substances play in the life of nerve tissue, we really possess very little positive knowledge of their true purpose. Indeed, we do not know how these bodies actually exist in the living tissue, as is well evidenced by the utter lack of agreement among physiological chemists as to the entity of the so-called protagon. Whether this phosphorized substance, studied by so many investigators, exists as such in the living tissue, or