Pancreatic 



juice 



(2) Veins from 

 intestine carry substance 

 from lining cells--" 



Modified blood, 

 brought by arteries 

 stimulates pancreas 

 ^,, to secrete 



vpy After meal dog's blood 

 ^ contains something that 



stimulates 

 pancreas of 

 an unfed 

 dog 



Pancreas 



Food getting 



into beginning 



of intestine 



stimulates 



lining cells 



HOW A CHEMICAL MESSENGER WAS DISCOVERED 



When some blood from a dog that has just been feeding is injected into the veins 

 of a dog that has been without food for several hours, the pancreas of the hungry 

 dog begins to secrete digestive juices. Otherwise the pancreas becomes active only 

 when food enters the intestine from the stomach 



and not at other times? Toward the end of the nineteenth century, two 

 British scientists, experimenting on dogs, found a surprising answer to these 

 questions. They could find no nerve connections to account for what hap- 

 pens. Instead they found that when food arrives in the intestine, some cells 

 in the wall of the intestine start producing a special substance, which is not, 

 however, discharged into the food cavity. This special substance is ab- 

 sorbed by the blood and carried off in the blood-stream. 



When blood containing this substance reaches the pancreas or the liver, 

 it starts the gland secreting its special product. How can we tell that it is 

 this something in the blood that sets ofl the gall bladder and the pancreas? 

 If we take some blood from a dog shortly after food has passed from the 

 stomach to the intestine, and inject it into the veins of a dog whose stomach 

 is empty, both pancreatic juice and bile will in a few moments appear in 

 the intestine of the second dog. William Maddock Baylies (1860-1924) and 

 Ernest Henry Starling (1866-1927), the experimenters, called this unknown 

 substance secretin, and described it as a hormone, from a Greek word mean- 



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