Animal Instincts and Tropisms 285 



mined by specific substances which also determine 

 the tropistic reaction (as well as phenomena of organ 

 formation, although this latter phenomenon has 

 nothing to do with the subject of instincts) ; and the 

 excellent work of Cannon' has shown the r61e of adre- 

 nalin in the expression of fear. It is, therefore, both 

 unwarranted and unnecessary to state that hypotheti- 

 cal emotions determine the tropistic reactions. 



* Cannon, W. B., Bodily Changes in Pain, Hunger, Fear, and Rage, 

 New York, 19 15. 



