PROBLEMS. 357 



versation. We can thus obtain some information 

 us to the effect of conversation upon the nerve- 

 centres of an exhausted man. Conversation may 

 excite or inhibit the separate discharges of the 

 nerve-centres, and may cause them to occur in 

 larger or smaller combinations; experiment alone 

 can demonstrate these points. 



(2) The amount of spontaneous finger movements 

 in an infant may be similarly demonstrated by 

 enumeration and by graphic records. 



(3) The effects of the sight and sound of objects 

 upon the action of the nerve-centres, and particu- 

 larly the effect in producing special combinations 

 of movements, will be shown best by taking tracings 

 of those movements. The time of the sight of an 

 object, or of hearing a sound, is easily indicated 

 on the tracing by the action of an electrical signal. 

 The inhibitory action of light upon the spontaneous 

 movements of an infant is shown by a tracing (see 

 Fig. 9, p. 101). 



(4) Applying motor tubes over all the joints 

 of the upper extremity, and enumerating the 

 movements, will show (a) the relative frequency 

 of movement of large parts as compared with small 

 joints; (6) if tracings be taken, the frequency of 

 interdifferentiation of movements will be demon- 

 strated ; that is, the frequency with which fingers 

 move without the elbow, or vice versa, etc. 



(5) Retentiveness, or permanent impressionability, 

 is best demonstrated by the graphic method. If 

 the same stimulus on different occasions produces 

 similar movements, we may conclude that the 



