COORDINATION 197 



select insulin which reaches the blood directly from the pancreas, 

 and is not delivered with the other secretions of this organ to the 

 intestine through the pancreatic duct. 



Diabetes has long been known to be the result of a deficiency 

 of a pancreatic function leading to a lack of coordination of the 

 chemical processes by which the body uses carbohydrates to sup- 

 ply energy. The storage of sugar by the liver is unregulated. Evi- 

 dences of this disease are chiefly an increase in the sugar content 

 of the blood and the presence of sugar in the urine. Now we know 

 that a close approach to the normal metabolic condition can be 

 attained by administering to diabetics the hormone insulin ex- 

 tracted from the pancreas of sheep or other animals. Insulin thus 

 takes the place of the secretion which the pancreas fails to afford, 

 and so removes the pall of hopelessness from many of the most 

 acute and desperate cases of diabetes. 



Turning now to a gland devoted solely to the secretion of a 

 hormone, we may select the thyroid which, as has been seen, arises 

 as an outpocketing of the digestive tract in the neck region and 

 finally loses all connection with its point of origin and becomes 

 a ductless gland. (Fig. 110.) 



The general effect of the thyroid hormone, thyroxine, on 

 metabolism is a regulation of the rate of oxidation in the body to 

 meet changing physiological demands. An excess of thyroxine 

 induces such vigorous fuel consumption that no surplus remains 

 in the body to be stored as fat; while a deficiency in the glandu- 

 lar secretion results in a tendency toward fat formation. The ad- 

 ministration of thyroid extract or thyroxine is often an efficient, 

 though dangerous, means of reducing fat by increasing the oxida- 

 tive processes of the body. A deficiency of the hormone during 

 adult life frequently results in a pathological condition called myx- 

 edema. Children in whom the development of the thyroid is sup- 

 pressed become dwarfish idiots known as cretins, while over- 

 development of the gland induces increased nervous activity and 

 mental disorders. Feeding with thyroid material prevents or re- 

 tards the development of cretinism and cures myxedema, while 

 a surgical removal of part of the gland may cure the nervous in- 

 stability and other symptoms due to an excessive amount of the 

 hormone. Goiter is a pathological enlargement of the thyroid due 

 to a deficiency in iodine needed to manufacture its iodine-contain- 

 ing thyroxine. 



