706 O. D. ANDERSON 



ning with the top line and proceeding downward. Figure 1 

 shows a typical record of the responses before the introduc- 

 tion of the differentiation problem (the negative stimulus 

 Met. 42). Note the quick movements of the head, before, 

 during and after the Met. 120 stimulation, the irregular respi- 

 ration, and the brisk flexion movements of the reaction leg 

 during the stimulus and at the end when the shock was ap- 

 plied. The animal stood fairly quiet before the sound was 

 presented. In figures 2 and 3, characteristic records after the 

 introduction of the differentiation problem are shown. In 

 figure 3, the negative Met. 42 was presented, and in figure 2 

 the positive Met. 120. In both note the increase in the fre- 

 quency of the spontaneous head movements, the numerous 

 shiftings of the body posture, the noticeably more disturbed 

 respiratory rhythm, and the appearance of restless, spon- 

 taneous movements of the reaction leg. Notice especially that 

 the conditioned leg movement response is nearly as vigorous 

 to the negative stimulus as to the positive. 



In figure 4, typical reactions of the same dog are shown 

 during the post-operative period after the parathyroid ex- 

 tract had been discontinued. Contrast this record with those 

 of figures 1, 2 and 3. The record shows a complete 5 minute 

 period between two positive stimuli. Note the weak, slow 

 and infrequent head movements, the almost complete absence 

 of body movements, the undisturbed respiration which is 

 hardly affected even during the conditioned leg reaction to 

 the first stimulus, an excessively weak response to the second 

 stimulus, and no spontaneous leg movements at all. As the 

 motor C-R weakened, its latent period was lengthened two- 

 fold. In the normal period, the average latent period of the 

 response was 2 seconds, while in the post-operative period 

 it was 5 seconds. This was in accord with the observation 

 that the dog was less alert in the latter period. 



The C-R in all phases of the experiment is represented 

 in text-figure 125. Note the sharp drop in the magnitude of 

 the ( -R following the operation, the revival of the response 

 for a short time during the administration of the para- 



