252 



cells were damaged. The next step was 

 to cut the duct of the pancreas so that 

 its digestive juice could not reach the 

 small intestine. Despite this the animal 

 did not get diabetes. By this time the ex- 

 istence of ductless glands was known, so 

 that it was easy to accept the idea that 

 Langerhans' "islands" of cells are duct- 

 less gland cells whose secretions diffuse 

 directly into the blood. It was evident 

 that the pancreas has two different kinds 

 of secreting cells; it is both a gland with 

 a duct and a ductless gland. It makes a 

 digestive juice and secretes an important 

 hormone. 



It was not until 192 i that two Cana- 

 dians, Banting and Best, succeeded in ob- 

 taining the honnone from the "islands of 

 Langerhans," in the pancreas of an ani- 

 mal. They called it insulin. They soon 

 discovered ways of injecting insulin into 

 the body of a human being who cannot 

 supply his own. See Figure 242. This 

 account of the discovery of insulin is 

 more or less typical of scientific discov- 

 eries. Read the paragraph again and then 

 do Exercises 3 and 4. 



A hormone valuable in emergencies. 

 Fear, anger, or excitement of any kind 

 stimulates two small glands each of 

 which fits like a small cap on the upper 

 end of a kidney. These are the adrenal 

 (ad-ree'nal) glands. The inner portion 

 of the glands secretes the hormone ad- 

 reiiin (ad-ren'in). When the body is at 

 rest the blood contains practically no 

 adrenin. When such emotions as fear or 

 great joy are aroused the glands secrete 

 actively and the adrenin acts almost in- 

 stantaneously. Professor Cannon of Har- 

 vard performed a large number of 

 experiments on cats with and without 



How a Complex Aiiimal Uses Food unit iv 



adrenal glands. He found that when an 

 animal is afraid or excited, when it is 

 fleeing or defending itself or attacking 

 an enemy, adrenin brings about changes 

 in the body all of which seem to fit the 

 animal for its emergency. For this reason 

 the adrenal glands are sometimes called 

 the "glands of combat." 



What are the changes caused by ad- 

 renin? You must look at many parts of 

 the body for your answer. The skin 

 becomes pale, and if the body were 

 transparent, you would see many of the 

 internal organs losing color too, for the 



blood vessels to all these organs are con- 

 stricted (made smaller), shutting off 

 much of the blood supply. Furthermore, 

 the adrenin has a direct effect on the in- 

 voluntary muscle cells. As a result the 

 digestive tract and some of the other ab- 

 dominal organs largely stop their ac- 

 tivities. The heart, on the other hand, 

 beats more forcibly. At the same time 

 the blood vessels to the skeletal muscles 

 and brain are made wider by the adrenin. 

 Because of these changes blood reaches 

 the brain and muscles faster and in larger 

 quantities. The air passages widen, M'ith 

 the result that more oxygen reaches the 

 lungs and the blood stream. The change 

 from glycogen to glucose is speeded up 

 in the liver. All of these changes bring 

 about more oxidation and release of 

 energy where it is needed, in the brain 

 and in the skeletal muscles. At the same 

 time if there is a wound and the blood 

 escapes, adrenin hastens clotting. The 

 body has automatically prepared itself 

 for flight or struggle with the enemy. 

 The animal with fur or feathers, further- 

 more, shows what we have come to 

 recognize as a sign of fear or rage, the 



