9 2 THE CAUSATION OF DISEASE. 



motor-end- pi ate of the striped muscle fibre, so that the motor- 

 nerve-ganglion-cell,* the nerve fibre, and motor-end-plate form 

 one continuous strand of protoplasm — a more or less inde- 

 pendent tissue unit — whereof the ganglion-cell forms the head 

 and governing portion ; for anything which cuts off its influ- 

 ence, whether it be destruction of the cell itself or a severance 

 of the nerve fibre, causes degeneration of the fibre thus de- 

 tached from the governing influence of the cell. 



If we study the development of the nerve fibre, we shall find 

 the axis cylinder first appearing ; next, the medullary sheath ; 

 and, finally, the neurilemma. 



Now, in progressive muscular atrophy, it is found that, so 

 far as we are able to observe, the process of dissolution of 

 motor- nerve-ganglion- cell and nerve fibre is an inversion of 

 the evolutionary process as above sketched. First, as regards 

 the cell : degeneration affects first the finer ramifications of the 

 branching processes ; these become less complex, and gradually 

 disappear ; soon the main stalks begin to fade away, leaving the 

 cell a mere round mass, which in course of time becomes 

 angular, and finally, it may be, disappears. As regards the 

 nerve fibre : the neurilemma is the first to disintegrate ; next the 

 medullary sheath breaks up ; and, finally, the primitive axis 

 cylinder degenerates. 



The above remarks upon the evolution and pathological dis- 

 solution of the motor- nerve- ganglion- cell and fibre apply with 

 equal force to the striped muscular fibre, which receives its 

 nerve supply therefrom ; but there is no need to give a detailed 

 account of the evolution and pathological dissolution of the 

 muscle-cell. It is sufficient to state that the one is, in large 

 measure, an exact inversion of the other. 



With the exception of these two examples of complex 

 ganglion-cell and complex muscle-cell, we are unable to trace 

 with any accuracy the evolution and pathological dissolution of 

 individual cells, and this for manifest reasons. Few, if any, 



* This term is, I think, preferable to "anterior ganglion cell," because it 

 can be applied to the similar ganglion cells (forming the so-called " nerve 

 nuclei ' of the brain) whence the motor cranial nerves take their origin. By 

 using the same term to denote all these fundamentally similar structures, 

 we at once mentally group them under the same head, and it is right that they 

 should be so grouped both for physiological and pathological purposes. 



