lO Foster, Physical Basis of Psychical Events. 



seen in the nervous mechanisms of sensation ; and fatigue 

 is more readily induced by artificial than by natural stimu- 

 lation; but when we come to deal with the nerve fibre by 

 itself (and in such cases the stimulation is almost neces- 

 sarily artificial), and with the mere transmission of nervous 

 impulses, apart from their terminal effects, we find that 

 exhaustion cannot be induced by even the most powerful 

 and prolonged excitation. 



Two views may be taken as to the nature of this 

 untiredness of the nerve fibre. It has been supposed on 

 the one hand that the molecular changes which constitute 

 the nervous impulse are of a nature wholly unlike the 

 changes which in all other living tissues lie at the bottom 

 of activity, that the changes in the nerve fibre involve no 

 consumption of energy. On the other hand it may be 

 urged that in the nerve fibre the nutritive changes are so 

 admirably balanced, and respond to the demands made 

 upon them with such exquisitely arranged swiftness, that 

 what is lost by action (and that we may assume to be 

 little, for the change of electric potential, even though 

 conspicuous, is exceedingly small) is at once, without loss 

 of time, made good. So far as I know, we do not possess 

 any crucial test to decide between these two views; we 

 have no exact proof in one direction or the other; but, on 

 the whole, the latter view may, from many considerations, 

 be taken as the more probable one. 



If, for instance, we pass from the nerve fibre itself, 

 which, as we have seen, is a part only of the nerve unit to 

 the whole unit, to the nerve cell or neurone in its entirety, 

 we find that the nutrition of this is exquisitely cared for. 

 In all living units, in all living cells, the nucleus presides, 

 governs, and determines the nutrition of the unit. If a 

 simple unicellular organism be divided into two parts, so 

 that the nucleus remains in one only of the two, the 

 nucleusless fragment, even though it be the larger one. 



