Oscllldtory AJjiistineiih. 117 



But when a limb assumes a special directive position through volun- 

 tary muscular action there is no rigid attachment, and the con- 

 stancy of the direction must of necessity he adjusted by the pro- 

 prioceptive system reinforced by vision or touch, or occasionally 

 by the proprioceptive system alone. Here it is impossible that oscil- 

 lation could be avoided, and oscillation is assuredly found. More- 

 over the better the mechanisms involved — the steadier the nerves in 

 popular parlance — the smaller and more uniform are the oscilla- 

 tions. This is well displayed in rifle shooting, particularly when 

 the barrel is unsupported. A good shot is aware of the tremor but 

 he is able to keep it regular and of small dimensions. Similarly 

 in all skilled actions, and skill will always mean precision of spatial 

 and temjjoral relations, a high degree of efficiency is only possible 

 if the oscillations arising from the adjusting mechanism remain 

 small. Equilibrists and wire-walkers are definitely aware of the 

 oscillatory effect, and consciously resort to fine rhythmic movement 

 to keep the centre of gravity not statically above the small base of 

 support but moving to and fro on either side. Excitement, self- 

 consciousness, lack of experience, strain, fatigue, etc., may in the 

 healthy body produce an extensive increase in the range of oscilla- 

 tion, whilst that exaggeration due to alcoholism, cerebellar disease, 

 senility, neurasthenia, etc., is well known. A small amount of 

 swaying of the upright body when the eyes are shut has often been 

 observed in health, but a marked oscillatory movement has a high 

 diagnostic value. The position of the eyeball is maintained by 

 muscular contraction, guided by macular vision and the proprio- 

 ceptive information sent up from the eyes muscles. But when a 

 static object is regarded steadily the visual axis is not immobile; 

 there is a slight range of tremor. That this delicate oscillation 

 plays some part in art, especially pointilistic art, has been suggested 

 by H. G. Keller and J. J. R. Macleod^. Again, it is possible that 

 in nystagmus Ave may find thu pathological amplification of a normal 

 rhythm^. That a voluntary fixation of a limb (using the term 

 limb in its widest sense) must of necessity Ije oscillatory is not 

 usually assumed in physiological literature, yet a little considera- 

 tion will show that this must exist. In dealing, therefore, with the 

 rhythm of neural discharge from the central nervous system to the 

 muscles, two possible causes must be borne in mind. There may be 

 an intrinsic periodicity in the nerve cell or nerve cell complex — i.e., 

 rhythmic discharge of each nerve cell or rhythm due to sequence of 



1 Po]nilav Sfieiioe .Monthly. November, 191 :!. 



■2 This has been stated precisely by Coppez. Archives li'OphthahnoIogie, vol. 3:i, p. .545. 



2a 



