348 PHYSIOLOGICAL CHEMISTRY 



tion of all concerned. Further, it is not at all impossible that the cere- 

 brosides, as well as lecithin and possibly cholesterin, may exist in the 

 living tissue combined with some one or more of the proteids present 

 there. Our lack of knowledge is deplorable, and yet, in the words of 

 Sir Michael Foster, this is one of the " master tissues " of the body. 

 Surely, considering the preeminent position and controlling influence 

 of this tissue, we may look for a speedy clearing away of the darkness 

 that enshrouds our understanding of the exact chemical composition 

 of nerve-tissue, and especially of the way these peculiar substances 

 of the myelin material exist in the living tissue. 



Again, we may ask ourselves what is the nature of the chemical 

 changes that take place in nerve-tissue; in the ganglionic cells of the 

 gray matter and in the axis cylinder of the nerve-fibres. When a 

 muscle contracts there is a measurable chemical decomposition. The 

 energy of muscular contraction comes from the breaking-down of 

 non-nitrogenous components of the muscle, and perhaps in some 

 measure from the decomposition of nitrogenous constituents. Fur- 

 ther, there is a liberation of heat, a development of lactic acids, etc. 

 When a stimulus is applied to a nerve, on the other hand, no such 

 manifestations of chemical action are apparent. The muscle to which 

 the nerve is attached contracts, the secreting cell pours forth the 

 product of its activity, etc., but there is no noticeable change in the 

 nerve itself, no recognizable liberation of heat, no change of reaction, 

 no output of carbonic acid, that can be detected. Are we to conclude, 

 then, that the axis cylinder of the nerve-fibre acts simply as a con- 

 ducting agent without itself undergoing any change? Is it to be com- 

 pared to an electric wire, with the surrounding myelin material, the 

 substance of Schwan, serving as a convenient insulating or protective 

 medium? If we are to accept this view, what are we to say regarding 

 the non-medullated fibres? Do not they need an insulating material 

 likewise? We can argue that the myelin substance is especially 

 adapted for the nourishment of the nerve, that its high potential 

 value renders it peculiarly suitable as a concentrated nutriment, and 

 that its intimate contact with the neuraxis and with the ganglionic 

 cells of gray matter proclaims its probable use in this direction. 

 Moreover, if we follow this line of argument still further, we may be 

 led to believe that the stimulation of a nerve, its power of conductiv- 

 ity, etc., are associated with chemical decompositions along its axis 

 as marked in their way as those that occur in a contracting muscle- 

 fibre. Truly, we have here a multitude of questions, for which at 

 present no satisfactory answers are to be found. The problems are 

 on the surface awaiting solution. 



Finally, emphasis must be laid upon a series of problems in physio- 

 logical chemistry, true solution of which will do much to explain 

 natural and artificial immunity, the action of toxins and antitoxins, 



