No. 2.] 



CHANGES /AT NERVE CELLS. 



139 



before producing complete exhaustion. The fatigue curve of a 

 nerve fibre has been shown, for short intervals at least, to be a 

 straight line which remains parallel to its base line; i.e. within 

 physiological limits a nerve fibre is not susceptible of fatigue 

 (8 ; 9 ; 79 ; 40). 



No curve representing fatigue of the nerve cell, .drawn directly 

 from observation of the cell itself, has hitherto been made. The 

 nearest approach to this is to be found in such work as Mosso 

 (54, pp. 175, 185, 186) and Lombard (44, Figs. 3 and 5) have 

 done for the fatigue which manifests itself in voluntary muscu- 

 lar contractions (Mosso, see plates pp. 178, 185, 186; Lombard, 

 see PI. II, Fig. 5). If, as would seem demonstrated, the curve 

 which these investigators find, expresses, in some way, the 

 fatigue of the brain or spinal cord cells, we may say that the 

 nerve cell tires rapidly at first, then slowly, or possibly gains a 

 little or holds its own for some time, and at last falls quite 

 rapidly again to a state of complete exhaustion. It is not 

 possible, of course, to say whether any nerve cell, even the 

 most shrunken and vacuolated to be found, has been entirely 

 exhausted ; probably not ; so the end of our curve will not be 

 complete. But if we now plot the percentages given in table 

 VII for a fatigue series, we find a curve quite similar to those 

 obtained by Mosso and Lombard. 



We have from the table slight stimulation, for one hour, two 

 and one-half hours, five hours, and ten hours, causing a shrink- 



age in the volume of the cell nucleus of respectively 22 percent, 

 21 per cent, 24.3 per cent, and 43.9 per cent. This is repre- 

 sented to the eye by the dotted line in Fig. i. For the first 

 hour the nuclei shrink rapidly, for three or four hours they 

 almost hold their own, and then shrink quite rapidly again. 



