78 CRILE— PHYLOGENETIC ASSOCIATION [April 22, 



ception, the respiration, the mechanism for erecting the hair, the 

 sweat glands, the thyroid gland, the adrenal gland (Cannon), and 

 the special senses. On the other hand the entire digestive and pro- 

 creative functions are inhibited. What is the significance of this 

 grouping? So far as we know the organs stimulated increase the 

 efficiency of the animal for fight or for flight. It is through skeletal 

 muscles that the physical attack or escape is affected; these muscles 

 alone energize the claws, the teeth, the hoofs, and the means for 

 flight. The increased action of muscles of the heart and the blood 

 vessels increases the efficiency of the circulation; the secretion of the 

 adrenal gland causes a rise in the blood pressure ; the increased 

 action of the thyroid gland causes an increased metabolic activity ; 

 there is evidence that glycogen is actively called out, it being the 

 most immediately available substance for the production of energy ; 

 the increased activity of the respiration is needed to supply the 

 greater requirements of oxygen and the elimination of the increased 

 amount of waste products; the dilation of the nostrils affords a 

 freer intake of air; the increased activity of the sweat glands is 

 needed to regulate the rising temperature of the body from the in- 

 creased metabolism. The activity of all of the organs of perception 

 — sight, hearing, smell — are heightened for the purpose of more ac- 

 curately perceiving the danger. It can not be a mere coincidence 

 that the organs and the tissues that are stimulated in the emotion 

 of fear are precisely those that are actuall)^ utilized in the percep- 

 tion of danger in a physical struggle for self-preservation. 



Are there any other organs stimulated by fear except those that 

 can or that do assist in making a defensive struggle? I know of 

 none. On the other hand, if an animal could dispense with his 

 bulky digestive organs, whose functions are suspended by fear, if 

 he could, so to speak, clear his decks for battle, it would be advan- 

 tageous. Although the marvelous versatility of natural selection 

 apparently could devise no means of affording this advantage, it 

 shut off the nervous current and saved the vital force these non- 

 combatants ordinarily consume in the performance of their func- 

 tions. Whatever the origin of fear is, its phenomena are due to a 

 stimulation of all of the organs and tissues that add to the efficiency 



