i62 POPULAR SCIENCE MONTHLY. 



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 accom- 

 pany 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 and the transformations that occur when these fluids are withdrawn 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 con- 

 figuration 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 sug- 

 gests 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 sur- 

 rounding 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 stri- 

 kingly 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 cere- 

 brosides contain a carbohydrate group yielding galactose on decomposi- 

 tion, 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 func- 

 tion 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 sub- 

 stances 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 



