CHEMICAL REGULATORS 397 



was shown to have an equally important role as a ductless gland, 

 producing hormones. Von Mering and Minkowski showed that its 

 extirpation was followed in all cases by the appearance of sugar in 

 the urine. Evidence has accumulated indicating that the oval or 

 spherical islands of Langerhans, that are embedded in the pancreatic 

 tissue, are the source of the hormone now called insulin, which 

 regulates the sugar metabolism of the body. 



The story of the long struggle of scientists to demonstrate the 

 existence of this hormone is a fascinating one. Banting, Best, and 

 Alacleod ^ in 1921 gave the first successful demonstration of the 

 isolation of insulin. We now know that the general physical and 

 mental condition of people suffering from diabetes can be markedly 

 improved through the administration of this hormone. While the 

 exact nature of the reaction is not fully understood, it is certain that 

 the amount of sugar in the blood stream is reduced sharply after the 

 injection of insulin. 



Growth Regulators 



Thyroid 



One must think of the thyroid as a gland with a dual function. We 

 have already noted the effect which the secretions of this gland have 

 upon general metabolism. The second effect is its influence upon 

 growth. When the thyroid is removed in young dogs, for example, a 

 retardation of growth occurs in a few weeks. These experiments 

 substantiate observations made upon children with congenital lack 

 of thyroid. 



Gonads and Pituitary 



As will be noted in more detail later, these glands are both associated 

 with growth, and play an imj^ortant role in the normal development of 

 the individual. 



Pineal 



Although the function of the pineal gland is not clear, it should be 

 mentioned at this point. It is a small body which appears in nearly 

 all vertebrates as an outgrowth from the roof of the 'twixt-brain 

 (diencephalon). The pineal body reaches its greatest development in 

 man at about the seventh year. After that age, and particularly 



' Banting, Best, Macleod. Am. Jour. Physiol., 59 : 479. 1922. 



