THE VERTEBRATE BODY 363 



their environment result from the action of this hormone. The hor- 

 mone is also produced in man, but it does not affect his skin color and 

 no other function of the hormone has been discovered. 



An extract of the posterior lobe, pituitrin, has been found to have 

 three major effects on the body. It causes a constriction of the small 

 blood vessels with a consequent elevation of blood pressure (pressor 

 action). It inhibits the loss of fluid through the kidneys (antidiuretic 

 action). It stimulates the smooth muscles, especially the muscles of 

 the uterus of the female (oxytocic action). It has been possible to 

 separate the extract of the posterior lobe into two hormones. One, 

 known as pitressin, affects the blood pressure and the kidneys; the 

 other, known as pitocin, has the uterine-stimulating property. This 

 latter hormone is valuable in obstetrics because it gives physicians a 

 method to stimulate uterine contractions during difficult childbirth. 

 When there is a deficiency of pitressin, a person will excrete great quan- 

 tities of a very dilute urine and will consequently have a great thirst 

 which causes him to drink large quantities of water. This condition is 

 known as diabetes insipidus, but it bears no relation to the diabetes mel- 

 litus, or sugar diabetes caused by insulin deficiency. Injections of 

 pituitrin or pitressin relieves the symptoms of diabetes insipidus. 



The anterior lobe of the pituitary is probably the most important 

 endocrine gland in the body. It is sometimes called the master gland 

 because it exerts controlling influences over other glands of the body. 

 It seems to produce not one, but numerous hormones with various func- 

 tions. The first of these to be discovered was the growth hormone. 

 When this hormone becomes overabundant in a child it leads to unusual 

 bone growth and results in gigantism, whereas dwarfism results from its 

 deficiency. When it becomes overabundant after bone growth has 

 ceased it stimulates bone growth in restricted areas such as the face, 

 hands, and feet, causing a painful deformity known as acromegaly. 



Later it was found that this gland secreted a gonadotropic, or gonad- 

 stimulating, hormone. Young male animals injected with this hormone 

 showed greatly accelerated sexual development and greatly enlarged 

 testes. Male baby chicks developed combs, spurs, and attempted to crow 

 and mate with baby females at the age of six weeks. In the female the 

 hormone serves to regulate the reproductive cycle by stimulating the 

 production of estrogen and progesterone. Unfortunately, this hormone 

 is very unstable and quickly loses its potency in solution, but it has now 

 been prepared in a crystalized form that can be stored and used medi- 

 cally. Infantile sexual organs in a woman and the resulting sterility 

 may sometimes be corrected by injections of this hormone. Cryptorch- 

 ism, failure of the testes to descend into the scrotum, and similar evi- 



