GENETIC TYPE AND THE ENDOCRINES 659 



perimenter is seen at the door, the dogs become excited and 

 run and jump about in a frenzy of motion and friendly 

 barking. The same friendly overtures may be made to a 

 complete stranger. When taken into the laboratory on the 

 leash, the dog usually leads the way with erect head and 

 wagging tail. He does not need to be dragged along. The 

 Leash may be removed when the laboratory is approached, 

 and the dog will go at once and stand upon the platform in 

 position, ready for tbe experiment. This is equally true 

 whether food or shock are to be presented. During the ex- 

 periment, the average dog salivates freely when the metro- 

 nome to be followed by food is sounded, and the paw is 

 vigorously raised at the clicking to be followed by the shock. 



During the formation and stabilization of the reflex, two 

 observations were made which indicate clearly the value of 

 the conditioned reflex in studies of this sort. The C-R varied 

 with subtle and delicate natural changes in the physiological 

 stales of the animal. The reflex is altered in a female in 

 heat or while lactating. The magnitude of the salivary C-R 

 was strikingly increased during the oestrus in an animal 

 which normally gave a very weak response or none at all. 

 A similar observation was made in Pavlov's laboratory by 

 Kreps ('23). 



Such conditions are illustrated by plate 108 and text-figure 

 115. Figure 1 (pi. 108) shows the absence of a conditioned 

 salivation and the head and body movements when the dog- 

 was not in heat. Figure 2 (pi. 108) shows a typical strong 

 salivary C-R accompanied by vigorous head reaction when 

 the animal was at the height of the oestrus. In text-figure 

 115, the chart 7 shows the complete course of the C-R through- 

 out a 4-month cycle, an inactive followed by an active phase. 



' In all charts each bar represents the magnitude of the C-R evoked by a single 

 application of the metronome. Only one trial out of a day's trials of positive- 

 negative-positive stimuli was counted. It was the first positive conditioned 

 stimulus (excepting the initial short, priming stimulus). This was selected as 

 evoking the most characteristic response of the day's reactions, the one not being 

 affected by "successive inhibition" from the preceding negative stimulus. 



The magnitude of the selected response is expressed in 1/100 cc. for the 

 salivary C-R and in mm. for the motor C-R. The ordinate shows these values. 

 The duration of the experiment in months is shown on the abscissa. 



