484 REPORTS ON THE STATE OF SCIENCE. 



spite of all voluntary efforts to the contrary, passes on from feature to 

 feature or plays to and fro over the object of thought. 



In all these cases we seem to be dealing with a rise of the resistance 

 of a nervous path rapidly induced by its activity and as rapidly passing 

 away ; a rise uf resistance which serves to divert the excitation process 

 from the path to some other channel, and so to prevent the injurious 

 effects of a too-prolonged activity of any one path. 



These are manifestations of local fatigue, of increase of the ratio of 

 resistance to energy, induced not by diminution of energy, but by increase 

 of strictly local resistance. 



Again, experiments with the ergograph have been used much in the study 

 of fatigue, but one vei-y interesting feature of such experiments has been 

 unduly neglected I think. I draw your attention to it in this connection, 

 because it seems to bear out the view I am setting forth. 



The subject of the experiment has to lift a heavy weight repeatedly at 

 brief intervals, by bending as far as he can his middle finger. Fatigue 

 very soon manifests itself in the form of a diminished extent of the bend- 

 ings of the finger. Now if you carefully observe the subject as he con- 

 tinues to repeat his efforts, you will usually see that, while at first he 

 contracts only the muscles immediately concerned in the flexion of the 

 finger, other muscles come into play as the flexions become diminished in 

 extent ; first the muscles of the upper arm, then those of the shoulder, 

 then those of the trunk, still later the muscles of the lower limbs and of 

 the arm and shoulder of the opposite side, and even those of the face, jaw, 

 and neck on both sides. There takes place, in short, a spread or march of 

 the excitation (not unlike the march of Jacksonian epilepsy) from the 

 motor tract directly concerned in producing the flexion of the finger to 

 adjacent motor tracts, then to successively more distant tracts. 



Now this is just what must occur if, while the supply of liberated 

 nervous energy is maintained at a high level of potential, and while the 

 subject continues to direct it towards the one set of muscles, the resist- 

 ances of the paths through which the excitation i-eaches the muscles are 

 liable to be rapidly raised owing to the intensity of the process and to its 

 repetition at brief intervals. The excitation will overflow, first into the 

 most nearly connected tracts ; later into those successively more remote, 

 as the resistances of the more nearly connected tracts become in turn 

 increased. 



A very brief rest suffices to abolish, or to diminish in very large 

 degree, any fatigue symptoms induced by ei'gographic work ; and if in 

 the ergographic experiments the intervals between successive bendings of 

 the finger are made equal to several seconds, the evidences of fatigue are 

 much diminished. 



We have then abundant evidence of the rapid production of local 

 increase of resistance in the central nervous system ; and all that we know 

 of the cell-bodies and of the axis cylinders makes it improbable that they 

 can be the seats of these rapidly induced and, very transitory local 

 increases of resistance. Further, the fact that these local increases of 

 resistance seem to be most rapidly induced in the higher levels of the 

 central nervous system, where the connections between neurones must be 

 regarded as least intimate and fixed, and to be least rapidly induced in 

 the reflex arcs of the spinal cord, where the connections between afferent and 

 efferent neurones are most firmly established, is in harmony with the view 

 I am defending and seems unintelligible if the alternative view be adopted. 



