INTERDEPENDENCE OF ORGANS 67 



these reactions place at the disposal of the muscles and nerv- 

 ous system the conditions for maintaining intense work for 

 comparatively brief periods of time, and all this is done by 

 the simple expedient of discharging from one of the organs 

 of the body an internal secretion on the blood. 



Finally, that adrenaline does in fact serve the purpose of 

 placing the body in condition to perform intense muscular 

 work is rendered probable by the discovery that conditions 

 of emotional excitement, especially those of fear or anger, 

 cause the discharge of nervous impulses to the adrenals. 

 Among animals it is these very emotions which accompany 

 or at least precede the most vigorous muscular activity, 

 fear going along with flight and anger with combat. This 

 suggests that these emotions serve the purpose of calling 

 forth the utmost of which the animal is capable in preserving 

 its very existence. 



5. Other examples of internal secretion. An equally re- 

 markable discovery has shown that the pancreas not only 

 manufactures an important digestive juice (pancreatic juice) 

 which it discharges into the intestine through its duct (pan- 

 creatic duct, see Fig. 54) but also produces another sub- 

 stance which is necessary, in order that other organs may 

 use the sugar which is in their food. Here we have an ex- 

 ample of an organ which produces both an ordinary and 

 an internal secretion, and the same thing seems to be true 

 of the kidney, as it certainly is of the liver. 



Much attention has recently been given to the study of 

 another ductless gland, the pituitary body, situated in the 

 bone between the roof of the nasal cavity and the base of 

 the brain (see Fig. 14). There is good reason for thinking 

 that this gland contributes an important internal secretion 

 to the blood and that certain organs of the body fail to act 

 normally when this secretion is deficient ; serious results also 

 follow an excessive secretion. Incidentally it may be men- 

 tioned that it is widely held that excessive secretion of the 



