On the Relation of Muscle Sense to Pressure Sense 17 



ulations in the lifting member than the same change of stimulus 

 in passive pressure. The heavier pressure will arouse local signs 

 in more widely separated areas of the member, that is, they will 

 irradiate out farther from the point of contact with the cork and 

 so they will be recognized as coming from different localities. 

 As the whole hand and arm are active, the irradiations due to the 

 increased pressure, where they tend to increase, must take place 

 in a single direction up the arm or arrange themselves in some- 

 thing like a serial order. The errors of judgment upon the stand- 

 ard are about the same as in passive pressure, but the chances 

 that new stimulations will arise by which a heavier pressure may 

 be inferred are greater, and thus follows the decrease in threshold 

 of discrimination. When the changes occur in a locally serial 

 order rather than first along one radius and then along another, 

 each change will be more likely to aft"ect a local sign that ha? 

 been unaffected by a different, that is, a lighter pressure, and so 

 give a basis for the judgment of heavier. When, however, the 

 pressures approach one another, there will be the same tendency 

 for different pressures to invade the same areas with their stimu- 

 lations and thus give a realm of uncertainty in which the judg- 

 ments may fall either way, depending upon the probability that 

 the stimulations arouse local signs that are not stimulated by 

 other pressures. 



These occasionally excited local signs may be looked upon as 

 being included for passive pressure within a circular area sur- 

 rounding that within which lie the local signs most frequently 

 excited by the standard. The occasionally excited local signs 

 may then vary by extending out upon any radius from a center 

 which is the point of application for the pressure. For active 

 pressure these occasionally excited local signs lie along several 

 radii that extend out from the point of application on a single 

 side ; the possible directions in which they may vary are less than 

 for passive pressure. Could we now find a muscle group which 

 in making discriminations varied only in a single direction, the 

 discriminations must become more certain in proportion as the 

 muscle is possessed of a high degree of nervous control. Such 

 muscle groups are found about the eyes. The contractions taking 



191 



