576 Journal of Comparative ISfeurology and Psychology. 



end takes the lead in locomotion on account of its greater adaptation 

 for extension, and also since its longitudinal muscles are not developed 

 especially more than elsewhere it would perhaps be less under the 

 influence of a general inhibition of extension in the case of maximum 

 shrinking movements. 



Frequency of the Reaction Types under Different Degrees of 

 Stimulation. — A statistical presentation of the results of stimulation 

 is necessary to give adequate account of the relative frequency of the 

 different types. The subjoined table I shows the occurrence of the 

 different reaction types under different degrees of stimulation, each 

 type in Fig. 2 being represented by its curve. It will be seen that 

 the different types culminate at different points. Type I has its highest 

 frequency with a stimulus not exceeding 1/32 per cent HCl. Behavior 

 under similar stimulation with tap water showed almost uniformly 

 indifferent results, indicating that with proper care in applying the 

 stimulus mechanical irritation may be practically eliminated. The 

 frequency of type I falls off rapidly. The second type culminates 

 with a strength of stimulus equal to !/§ per cent and falls off rapidly 

 thereafter. Type III begins to appear with a relatively weak stimulus 

 but culminates at I/2 P^r cent. Type IV appears first wath a stim- 

 ulus of 1/4 per cent HCl. and culminates at about 1 per cent. It 

 does not become a predominant reaction at any time and in this 

 respect differs from the others, each of which with some strength of 

 stmiulus becomes the prevailing type of response. The fifth attains 

 its maximum with 10 per cent acid. 



Variahility of the Types. — The table shows the results of the inter- 

 action of external stimulus and physiological state, the succession of 

 types corresponding to increase of stimulus and the extent of each 

 type indicating a variability in the physiological receptivity among 

 different individuals. This variability would appear less in a classi- 

 fication based solely upon the initial phases of the reactions. For 

 example, those cases of type III that appear in the 10 per cent 

 column nearly all began with the leaping movement. Those in the 

 14 per cent column began with a weak shrinking movement. Each 

 type exhibits an increase in intensity. Type II also shows a wide 

 range of variability, for types II and V are both, according to defini- 



