234 Heredity and Environment 



istered early enough in such cases the most wonderful improve- 

 ment is brought about; the body frequently assumes normal 

 proportions and features and the mind becomes bright and active. 



Another gland of internal secretion which plays a great part 

 in the development of body and mind is the pituitary, or hypo- 

 physis, which lies on the ventral side of the brain ;. it consists of 

 two parts, an anterior portion derived embryologically from the 

 roof of the mouth, and a posterior portion which came from the 

 floor of the brain. Excessive secretion of the anterior portion 

 stimulates the growth of the bones and if this occurs in early life 

 it leads to a great lengthening of the bones, especially of the arms 

 and legs, and in later life the bones of the hands, feet and face 

 becomes enlarged so that the subject becomes a giant, though often 

 with weakened body and mind ; on the other hand if there is de- 

 ficiency of secretion from the anterior pituitary there is a general 

 dwarfing of the body. The secretion of the posterior pituitary 

 acts as a stimulant to nerve cells, involuntary muscles and to the 

 sex glands ; deficiency of this secretion causes persistent "infantil- 

 ism" or sexual immaturity. 



Another pair of glands of internal secretion which exercise a 

 profound influence on both the structures and functions of the 

 body are the adrenals, or suprarenals, located just above the kid- 

 neys. These glands also are composed of two parts which produce 

 secretions differing in their physiological action, namely, a central 

 part or medulla and a superficial part or cortex. The secretion 

 of the medulla is known as adrenin or epinephrin and when intro- 

 duced into the blood it strengthens the heart beat and causes the 

 blood to be driven from the abdominal viscera to the skeletal mus- 

 cles, heart, lungs and brain. It also causes the liver to set free, 

 into the blood, sugar, which is "the optimum source of muscular 

 energy" ; it quickly restores fatigued muscle and increases the 

 coagulability of the blood Cannon lias shown that in emotional 

 excitement, such as pain, hunger, fear, or rage, there is increased 

 secretion of adrenin into the blood, and he has called attention to 



