2 HARRY MILES JOHNSON 



those in response to "non-essential" properties are called "con- 

 ditioned" reflexes. 



The following experimental procedure is followed: "A nor- 

 mally active and healthy dog of vigorous salivary reaction 

 having been selected, the duct of one of the salivary glands — 

 the parotid for example^is exposed on the outer surface of the 

 cheek and a salivary fistula is formed. The wound heals com- 

 pletely within a few days and the dog exhibits no signs of dis- 

 comfort or inconvenience. Those who have used the method 

 insist, indeed, that their animals are perfectly normal." Devices 

 are applied to catch and measure the saliva secreted in different 

 intervals of time. 



In the auditory tests the animal is accustomed to being fed 

 at a certain tone or sound until the saliva secretion begins when 

 the sound is made. Unfamiliar sounds do not provoke *the reac- 

 tion. Selionyi reports that discrimination was established by 

 this method between tones only a quarter of a tone different in 

 pitch. Further difference-diminution than this did not produce 

 such marked difference in secretion: if the two tones were very 

 near together in pitch, the "unfamiliar" one provoked a secre- 

 tory response, but not to such a degree of intensity as did the 

 "familiar" one. If the "familiar" tone was sounded too faintly, 

 however, the reflex conditioned by it was either very weak or 

 else did not appear. If an unfamiliar tone the pitch of which 

 differed very slightly from that of the familiar tone were given 

 just before the familiar one was sounded, the reflex condi- 

 tioned by the latter was partially inhibited. 



Yerkes has remarked that there are several obvious disad- 

 vantages attached to this method: "conditioned reflexes" die 

 out with repeated stimulation; the quality of food given con- 

 ditions a remarkable variation in the flow; and the rate of 

 secretion is conditioned also by the time -interval between stim- 

 uli. To this I would add the suggestion that there may be also 

 a tendency to rhythmical change in the rate and quantity of 

 secretion. Moreover, Selionyi tells us that the animal was 

 affected by the "kind of movements" made by the experi- 

 menter, who had to be careful neither to move too quicldy nor 

 to hold himself too rigidly quiet. As slight changes of posture 

 are very often involuntary there is room for doubt whether they 



