296 THE MAINTENANCE OF THE INDIVIDUAL 



and sugar appears in the urine, diabetes, a disease caused by a 

 dearth of insulin in the blood, occurs. Insuhn is a hormone* formed by 

 groups of cells collectively called the islands of Langcrhans, which 

 function as ductless glands. Since 1921, when Banting, Best, and 

 Macleod found that insulin injected into animals showing symptoms 

 of diabetes caused a decrease of sugar in blood and urine, this pan- 

 creatic hormone has become a veritable lifesaver to man. 



The Liver. The liver is the largest gland in the body, and in man 

 is found just below the diaphragm, a little to the right of the mid 

 line of the body. It is not primarily a digestive gland, although it 

 secretes daily about a quart of bile, which while containing no en- 

 zymes may have the power of rendering the lipase of the pancreatic 

 fluid more active. Bile when mixed with the pancreatic juice helps 

 emulsify liquid fats into minute separate droplets, in this way pre- 

 paring them for digestion. Certain substances in the bile aid espe- 

 cially in the absorption of fats. Another important function of bile 

 is the neutralization (wholly or in part) of the acid chyme when 

 it enters the duodenum, thus preparing it for the action of the 

 pancreatic juice. Bile also stimulates the peristaltic movements of 

 the intestine, thus preventing extreme constipation. It is also thought 

 by some to have a slight antiseptic effect in the intestine. Bile seems 

 to he mostly a waste product from the blood. Its color is due to 

 certain substances wiiich result from the destruction of worn-out red 

 corpuscles of the blood. 



Besides these digestive and excretory functions the liver is also 

 concerned with the formation of a nitrogenous waste, urea, CO(NH2)2. 

 This product is largely ]:)roduced in the liver, whence it is transferred 

 to the blood and carried to the kidneys where it is excreted. 



Perhaps the most important function of the liver is the formation 

 and storing of an animal starch, or glycogen. The liver is supplied 

 with blood from two sources, some from the heart, but a greater 

 amount directly from the walls of the stomach and intestine. This 

 latter blood supply is very rich in food materials and from it the cells 

 of the liver take out sugars in the form of glucose (dextrose), which is 

 synthesized into animal starch in the liver. Glycogen is stored in 

 the liver until such time as energy is needed. It is then reconverted 

 to the monosaccharide form, glucose, and carried by the blood stream 

 to the tissues where it is oxidized with an accompanying release of 

 energy. A limited amount of glycogen may be found and stored 

 in the muscles and it is also thought to be produced from proteins and 



