No. 2.] CHANGES lAT NERVE CELLS. 131 



the phenomena of fatigue to precede and shade into those of 

 disease. 



Several facts connected with the research negative the objec- 

 tion ; none, not even the so-called pathological appearance of 

 the cells, give it any real support. In the first place, no patho- 

 logical factor, capable of affecting the spinal ganglia, has been 

 introduced into the experiments. Electrical stimulation is kept 

 within physiological limits, as shown by the fact, that the nerves 

 conduct impulses to their muscles throughout the experiment. 

 And most of all, the fact, that the change increases steadily in 

 amount, as stimulation is prolonged or intensified, would indicate 

 that we are dealing with normal processes of the active living 

 cell. 



But aside from considerations of a pathological nature, the 

 process of recovery in a tissue has an interest of its own, physio- 

 logical and hygienic, in no degree less than that which attaches 

 to the process of fatigue itself. The bearing of the literature 

 upon this point has already been discussed. We know that 

 the cells of the epidermis, from which the nerve cells are phylo- 

 genetically derived, are worn out and off and are replaced by 

 new cells produced by multiplication. This is doubtless true of 

 all stratified epithelia, lining surfaces, internal as well as external. 

 But in all these instances we have friction and contact with 

 foreign or irritating substances, the half-masticated food forced 

 through the narrow oesophagus, dry air passing rapidly in the 

 trachea, and urine in ureters and bladder. Friction we have in 

 the blood-vessels ; but who has ever found epithelial scales in 

 the blood such as occur in urine or in saliva .'* 



From what is known of the structure and development of the 

 nervous system, the gradual growth of the nerve fibre from the 

 cell, the length of time required for the regeneration of a 

 divided nerve, the lack of any evidence of fatigue in a nerve, 

 etc., it would seem as absurd to suppose that the nerve ele- 

 ments die out and are replaced as to advocate the daily destruc- 

 tion and rebuilding of the world's telegraphic systems. Cables 

 and wires and keys, accidents aside, are practically permanent ; 

 and so are the battery cells, the zincs and acids alone requiring 

 renewal. So that if it were proven that, after stimulation, the 

 cells of a spinal ganglion fail to recover, i.e. die out, and are 

 replaced by new cells, I should be free to admit that a pathologi- 



