652 O. D. ANDERSON 



presentation of the metronome stimulus (beating 120 times 

 per minute), followed at once by the shock. In the thoroughly 

 trained animal the sounding of the metronome thus reinforced 

 by the electrical stimulus constantly evoked vigorous de- 

 fensive flexion movements of the reaction limb. The duration 

 of the clicking metronome was always 10 seconds. 



The technique of recording graphically the food-taking and 

 the defensive reactions is best described by reference to 

 photographic and graphic records of the typical actions shown 

 by the animals in the two sets of circumstances (see figs. 1 

 and 2, pi. 107). Figure 1 shows the nature of the overt 

 reaction of an animal to the metronome which had previously 

 been followed many times by food; the photograph at the 

 left shows the pose just before the stimulus is sounded, and 

 at the right the reaction as soon as the clicks are heard. 

 From the sitting posture, the dog rises to his feet, turns his 

 head toward the place where food is presently to appear 

 and remains in this posture until actually given the food. 

 The conditioned salivary flow occurs while thus waiting. The 

 dog often looks upward and listens to the sound, then lowers 

 the head and gazes at the empty food pan in front of him. 

 Such raising and lowering of the head may take place several 

 times during the stimulation. When the food is presented, 

 the animal lowers the head and eats in a vigorous fashion. 

 Beneath these photographs is a kymographic record of the 

 food-taking reaction. The third line from the bottom marks 

 the conditioned metronome sound by means of an electro- 

 magnetic signal marker. The line below records by the same 

 means the presentation of the food at the end of the metro- 

 nome sound. The top line represents movements of the head ; 

 the upward and downward movements are shown in up and 

 down strokes of the line. To obtain this record a thread is 

 attached to the dog's head and connected with a reducing 

 lever which marks vertical motion upon the moving paper. 

 The line below records any gross or general movement of 

 the body. This record is made by the movements upon the 

 drum of a sensitive recording tambour connected with a 



