PRESENT PROBLEMS 347 



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 and the transformations that occur when these fluids are withdrawn 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-fibres and the changes that 

 occur when the fibres 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-fibres and ganglionic cells sug- 

 gests another problem in physiological chemistry, solution of which 

 has long been 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 sub- 

 stances, 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 indi- 

 cating that the function of the myelin is to nourish the more import- 

 ant 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 sub- 

 stance, studied by so many investigators, exists as such in the living 

 tissue, or whether it is simply an intimate mixture of lecithin, cerebrin, 

 and one or more other substances, is not yet settled to the satisfac- 



