166 TROPISMS 



by the parotid (one of the salivary glands) in the dog 

 can be collected and measured. The earlier physiological 

 workers had observed that in a dog which had often been 

 used for the study of the influence of eating upon the flow 

 of saliva, the saliva began to flow whenever the prepara- 

 tions for feeding were made before the eyes of the dog, 

 even when no food was given. Pawlow made use of this 

 fact to study quantitatively the "strength" of such asso- 

 ciative phenomena, which he terms "conditioned re- 

 flexes" (to escape the terminology and interpretations 

 of the introspective psychologist). 537 A fistula a of the 

 duct of the par otic gland allows the saliva to flow outside 

 the cavity of the mouth. This fistula is connected with a 

 long manometer which by a special air chamber arrange- 

 ment gives a considerable change in the height of the 

 meniscus for the secretion of as little as one drop of 

 saliva, The variations of the height of the column of 

 liquid in the manometer are observed outside of the room 

 where the dog is. For each dog which is to serve for 

 such experiments the meal is preceded by a certain signal, 

 the sounds of a metronome of definite rhythm, or a definite 

 musical sound, or a definite optical signal, and so forth, 

 which is to form the special conditioned reflex for this dog. 

 After a certain number of repetitions the association is 

 established and from now on the flow of saliva commences 

 from the dog's parotid when the typical signal is given. 

 It was found that the quantity of saliva excreted by the 

 signal changes in a definite sense and quantity when the 

 signal varies or when other conditions accompanying the 

 signal vary. 



a The writer is indebted for the details of Pawlow's method to a short 

 review by Dr. Morgulis.^ 533 



