INTEGRATION OF ACTIVITIES 155 



cortex is removed pro»stration and death soon follow. Deficiency of its 

 hormone interferes with carbohydrate metabolism, and the blood loses 

 most of its glucose. Sodium chloride is also lost from the plasma, the 

 osmotic properties of the blood are changed, and so the volume of blood 

 is diminished and blood pressure falls. Development of reproductive 

 cells is also stopped, and Addison's disease is partly caused by a cortical 

 defect. Many substances have been extracted from the cortex, the 

 potent ones all being chemically related to one another. The name 

 cortin has been given to the active principle, but it has not been 

 identified or isolated. 



The adrenal medulla produces the well-known adrenalin (C9H13O3N). 

 This hormone has been synthesized artificially. Its effect is to strengthen 

 and accelerate heartbeat, increase the glucose in the blood, whiten the 

 skin, dilate the pupils of the eyes, and erect the hair. In general its 

 action is the same as that of the thoracolumbar part of the autonomic 

 nervous system. One theory of adrenalin is that it is a stand-by for 

 emergencies. By its control of glucose in the blood, it has been supposed 

 to increase muscular power and resist fatigue. In fear and rage and great 

 excitement, adrenalin is increased, and the body is supposed to be able 

 to perform feats under such emotions which it could not normally do. 



The pancreas, though a digestive gland whose digestive secretion 

 flows through a duct, also produces a secretion which must diffuse out 

 to the blood. This secretion is called insulin. It is produced in certain 

 groups of cells, the islands of Langerhans, which in the embryo were 

 budded off from the digestive tubules but which lose all connection with 

 the duct. The function of insulin is to control sugar metabolism. 

 Failure of the supply of this hormone causes the disease known as 

 diabetes mellitus, excess of sugar in the blood and hence its presence 

 in the urine. The disease may be relieved by administering insulin 

 extracted from other animals, but it has to be injected into the blood 

 vessels, not taken by mouth, for insulin is destroyed by the digestive 

 enzymes. Also, its ^effect lasts only a few hours, hence it must be used 

 frequently. 



The pituitary gland, at the base of the brain, consists of two parts. 

 The anterior lobe is derived in the embryo from the roof of the pharynx, 

 the posterior lobe from the floor of the brain. The connection with the 

 pharynx is lost in the adult, but that with the brain persists. The ante- 

 rior lobe produces a variety of hormones, one affecting growth, several 

 affecting the sex organs, others acting on the thyroid, adrenal cortex, and 

 mammary glands. Because of this multiple activity, particularly in 

 control of other endocrine glands, the anterior pituitary is sometimes 

 spoken of as the "master gland." The growth hormone was first isolated 

 in 1944 as a pure protein. Oversuppiy of this hormone produces giants — 



