330 STUDIES IN INSECT LIFE, ETC. 



muscles into full activity is diminished or done 

 away with. 



Thirdly, the flow of adrenalin has marked effects 

 on the vascular system, and all of these effects 

 are helpful or advantageous to men in a condition 

 of rage or fear. Its sudden presence in the blood 

 drives the blood from the abdominal viscera into 

 the organs which are most wanted for active 

 combat : into " the central nervous system, the 

 lungs, the heart, and the active skeletal muscles/' 

 Again, in small quantities the secretion has a 

 stimulating effect upon the heart, and so it comes 

 about that when a greater amount of work is 

 demanded from the heart, with increased arterial 

 pressure, blood is delivered to the heart in greater 

 abundance, and the augmentation of the heart- 

 beat is thus co-ordinated with other functions 

 adapted to meet great emergencies. 



Then again numerous investigators have shown 

 that the injection of adrenalin into the blood 

 produces a dilatation of the bronchioles, or 

 ultimate passages of the lungs. The smooth 

 muscles of the lungs are relaxed and deep, and 

 rapid respiration, which is characteristic of all 

 animals in pain or in great emotional excitement, 

 is rendered more easy. 



