PROBLEMS OF PHYSIOLOGICAL CHEMISTRY. 16 



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whether it is simply an intimate mixture of lecithin, cerebrin and one 

 or more other substances, is not yet settled to the satisfaction of all con- 

 cerned. Further, it is not at all impossible that the cerebrosides, 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, con- 

 sidering 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 fibers ? When a muscle 

 contracts there is a measurable chemical decomposition. The energy 

 of muscular contraction comes from the breaking down of non-nitrog- 

 enous components of the muscle, and perhaps in some measure from 

 the decomposition of nitrogenous constituents. Further, there is a 

 liberation of heat, a development of lactic acid, 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 at- 

 tached 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 car- 

 bonic acid, that can be detected. Are we to conclude then that the 

 axis cylinder of the nerve fiber acts simply as a conducting agent with- 

 out itself undergoing any change? Is it to be compared 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 

 fibers? Do not they need an insulating material likewise? We can 

 argue that the myelin substance is especially adapted for the nourish- 

 ment 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 the 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 conductivity, etc., are associated with chemical 

 decompositions along its axis as marked in their way as those that occur 

 in a contracting muscle fiber. 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- 



