122 THE CHEMISTRY OF NERVES. [BOOK i. 



protagon. Obviously the fat of the white matter of the central 

 nervous system and of spinal nerves (of which fat by far the 

 greater part must exist in the medulla, and form nearly the whole 

 of the medulla) is a very complex body indeed, especially so if the 

 cholesterin exists in combination with the lecithin, or cerebrin (or 

 protagon). Being so complex it is naturally very unstable, and in- 

 deed, in its instability resembles proteid matter. Hence probably 

 the reason why the medulla changes so rapidly and so profoundly 

 after the death of the nerve. It seems moreover that a certain 

 though small quantity of proteid matter forms part of the medulla, 

 and it is possible that this exists in some kind of combination with 

 the complex fat ; but our knowledge on this point is imperfect. 



The presence in such large quantity of this complex fatty 

 medulla renders the chemical examination of the other consti- 

 tuents of a nerve very difficult, and our knowledge of the chemical 

 nature of, and of the chemical changes going on in the axis cylinder, 

 is very limited. Examined under the microscope the axis cylinder 

 gives the xanthoproteic reaction and other indications that it is 

 proteid in nature; beyond this we are largely confined to inferences. 

 We infer that its chemical nature is in a general way similar to that 

 of the cell substance of the nerve cell of which it is a process. We 

 infer that the chemical nature of the cell substance of a nerve 

 cell, being of the kind which is frequently called ' protoplasmic/ 

 is, in a general way, similar to that of other ' protoplasmic ' cells, 

 for instance of a leucocyte. Now where we can examine con- 

 veniently such cells we find, as we have said 30, the proteids 

 present in them to be some form of albumin, some form of globulin, 

 and either myosin itself, or antecedents of myosin, or some 'allied 

 body. In other words, the proteid basis of the kind of cell sub- 

 stance which is frequently spoken of as "undifferentiated proto- 

 plasm," does not, in its broad features, differ materially from the 

 proteid basis of that " differentiated protoplasm," which we have 

 called muscle substance. Hence we infer that in their broad 

 chemical features the axis cylinder of a nerve fibre and the cell 

 body of a nerve cell resemble the substance of a muscle fibre; 

 and this view is supported by the fact that both kreatin and lactic 

 acid are present as * extractives,' certainly in the central nervous 

 system, and probably in nerves. The resemblance is of course 

 only a general one ; there must be differences in chemical nature 

 between the axis cylinder which propagates a nervous impulse 

 without change of outward form and the muscle fibre which 

 contracts ; but we cannot at present state exactly what these 

 differences really are. 



After the fats of the medulla (and the much smaller quantity 

 of fat present in the axis cylinder), the proteids of the axis cylinder, 

 arid the other soluble substances present in one or the other, or 

 gathered round the nuclei of the neurilemma, have by various 

 means been dissolved out of a nerve fibre, certain substances still 



