MOTOR COORDINATIONS. 149 



reactions, we come upon the reciprocal innervation of the antagonistic 

 muscles that control the movement of a limb. 1 



First demonstrated for voluntary antagonistic muscles by Sherrington 2 

 in connection with the antagonistic muscles of the eye, it appears that 

 whenever one member of a pair of antagonistic muscles is stimulated 

 to action through the central nervous system, the other member tends 

 to corresponding relaxation. Apparently, all movements of the limbs, 

 voluntary as well as reflex, are conditioned by this reciprocal innerva- 

 tion of antagonistic muscles. Its value to the organism is obvious. 

 Unless the antagonistic muscle relaxed during the contraction of the 

 agonistic, the latter would be operating not only against its load, but 

 also against the tonus of the former. While reciprocal innervation is 

 not a mechanical necessity for the movement of the limbs, it seems to 

 be a physiological device to increase the efficiency of muscle contraction. 

 At any rate, it appears to be a fundamental and universal fact of 

 nervous motor coordination. Measurement of the adequacy of motor 

 coordination, as seen in reciprocal innervation of antagonistic muscles, 

 can not be made in human subjects by the direct methods that are 

 available in animals. A human experiment must depend on the move- 

 ment of the limb or organ to which the muscles are attached, rather 

 than on the action of extirpated muscle. In the voluntary movements 

 of a limb, the adequacy of reciprocal innervation may be indicated in 

 two ways. In its simplest form, it is indicated by the maximum 

 rapidity of movement, since only by the relaxation of the antagonistic 

 can the agonistic be the most effective in producing rapid motion of the 

 limb. In a succession of most rapid possible movements of a limb, a 

 measure of the adequacy of reciprocal innervation may be found in the 

 rate with which the oscillations of the limb may be produced. 



Both of these measurements are complicated under ordinary circum- 

 stances by a variety of conditions. The normal speed of voluntary 

 movements varies enormously. One may move the fingers and arms 

 at any one of a large variety of predetermined rates. The maximum 

 velocity is conditioned not merely by the mass of the moving member, 

 the strength of the muscles, and the adequacy of motor coordination 

 between antagonistics, but also by that highly complex mental fact 

 which we call will. If one found in a subject more rapid movements 

 of the arm as a consequence of the ingestion of a small amount of 

 alcohol, the problem of the origin of the change and its consequent 

 significance would involve an equation with an indefinite number of 

 unknown factors. Euphoria, increased determination, adaptation to 

 experimental demands, increased interest or attention, due perhaps to 

 absence of conflicting interests, lack of apprehension of the conse- 

 quences, indifference to discomfort, as well as increased strength of 



'Compare Isserlin, Kraepelin's Psychol. Arbeit., 1914, 6, p. 1. 



2 Shemngton, The Integrative Action of the Nervous System. New York, 1907. Also notes 

 in Proc. Royal Soc. of London, 1887, 42, p. 556, and 1SSS, 43, p. 407. 



