250 'Journal of Comparative Neurology and Psychology. 



III. SENSITIVENESS TO ELECTRIC STIMULUS, IN ITS RELATIONS 



TO AGE AND SEX. 



The measurements of sensitiveness to electrical stimulation which 

 are now to be presented were made in connection with the study of 

 the relation of age to rate of habit-formation, for the special pur- 

 pose of throwing light upon the interpretation of the data which have 

 just been considered. Had the experimenter's aim been to make a 

 thorough-going investigation of the limits of sensitiveness in the 

 dancer, other and more accurate methods would have been em- 

 ployed. But as matters stood, it seemed desirable to use for these 

 tests of sensitiveness the method of applying the stimulus that had 

 been used in the plasticity experiments themselves. 



In its especially adapted form, this method exhibited the follow- 

 ing points of importance. A current from a storage cell was used, 

 in connection with a calibrated Hasler inductorium,'^ as stimulus. 

 The strength of the induced current was regulated by moving the 

 secondary coil. By means of an interrupted circuit device similar to 

 that previously described^ the mouse was permitted to receive this 

 current through its fore feet. ^Miile one observer manipulated 

 the keys of the circuits and regulated the strength of the cur- 

 rent, another placed the mouse in position and observed its be- 

 havior When it received the shock. Determination was made, 

 by repeated trials, of the lowest stimulus strength to which a definite 

 motor response was given, and of the strength to which only an 

 uncertain response was given. The average of these two results 

 was accepted as the iJireshold value for the individual. 



Twenty male and twenty female dancers were tested on two differ- 

 ent days. The results in terms of the position of the secondary 

 coil, as they appear in Table 8, indicate: (1) That the males are 

 somewhat more sensitive than the females. This difference, which, 

 according to the calibration curve of the inductorium, is nearly 

 ten per cent., was not evident to the experimenter as he worked 

 with the dancers from day to day in the training tests. (2) There 

 is no indication of change of sensitiveness with increase in age. 



'For the use of this inductorium I am inclebted to Dr. E. G. Martin. 

 'The Dancing Mouse, p. 94. 



