96 ENDOCRINE THERAPEUTICS 



The posterior lobe consists of two parts, the 

 pars nervosa, composed of neuroglia, and the pars 

 intermedia, a thin layer, ectodermic in origin, 

 applied to and partially surrounding the pars 

 nervosa. Functionally the pars intermedia is 

 associated with the pars nervosa, and the posterior 

 lobe has apparently an entirely different role from 

 that of the anterior lobe. This is shown by the 

 observation that removal of the entire gland, or 

 of the anterior lobe, is followed by death in a few 

 days, although the animal survives after the 

 removal of the posterior lobe alone. The 

 anterior lobe is therefore essential to life, whereas 

 the posterior is not. Partial removal or injury 

 by disease hi young animals produces more or 

 less deficiency of growth, failure of sexual develop- 

 ment, and often obesity ; mental development 

 is not nearly so affected as in thyroid deficiency. 

 When this arrest of pituitary development occurs 

 in the human subject it is known as infantilism. 

 The failure in growth and sexual development is 

 due to incomplete action of the pars anterior, the 

 obesity is believed to be due to partial failure of 

 the pars posterior. Overgrowth of the pars 

 anterior in man causes acromegaly, the chief 

 features of which disease are enlargement of the 

 bones, especially of the hands, feet, and face, 



