NERVOUS AND ENDOCRINE CONTROL 1 43 



If these islets are incapacitated in some way an insufficiency of insulin 

 occurs and a condition known as diabetes (diabetes mellitus) results. A 

 characteristic symptom of this' form of diabetes is increase of sugar in the 

 urine. Sugar is the most available source of energy in the body and a simple 

 sugar known as glucose is always present normally in the blood to the 

 extent of o. i to 0.15 of i per cent. It is easily oxidized, hence most of our 

 body heat comes from the burning of this sugar. When the sugar metab- 

 olism of the body becomes so defective that sugar is constantly wasted, 

 through the urine, the condition is therefore a serious one. Insulin is now 

 widely used in the treatment of diabetes and is restoring the general health 

 and prolonging the Hves of many persons. Its discovery has meant for 

 diabetics a change from a life expectancy of two or three years to one 

 of twenty or more. Sir Henry Dale has depicted the helplessness of the 

 physician of only a few years ago when confronted by this then dreaded 

 disease, in the following words: "As a student in the medical wards, I re- 

 member hearing a great physician, faced with a case of diabetes, express 

 the view that it would have been better for the patient if his condition 

 had not been discovered." 



It is interesting to note in this connection also that secretion of the 

 pancreatic digestive fluid itself does not proceed until the pancreas is 

 stimulated by a hormone known as secreti?i. Secretin in turn is produced 

 in the walls of the small intestine as a result of the entrance of the acid 

 contents of the stomach following gastric digestion. 



The human thyroid gland consists of two lobes attached to the sides of 

 the lower larynx, connected by a narrow band across the mid-line. That 

 of an average-sized, normal man weighs from 20 to 25 grams. It is slightly 

 larger per unit of body weight in women, and still relatively larger in chil- 

 dren. Its secretion plays a very important part in maintaining a proper 

 balance of the nutritional and growth processes. The active principle, 

 known as thyroxhi, has been isolated in the form of an organic iodine com- 

 pound containing no less than 60 per cent, of iodine. It is now prepared 

 synthetically by chemists. 



Thyroxin operates apparently by regulating oxidation rate. Overabun- 

 dance of its secretion {hyperthyroidis77i) speeds up the heartbeat, causes 

 higher temperature by raising the metabolic rate of body cells some 30 

 per cent or more, increases perspiration and, in general, overstimulates the 

 body activities. Hyperthyroid persons are usually highly nervous, over- 

 active and emotionally unstable. A condition known as exophthalmic or 

 toxic goiter, characterized by bulging eyes, excitability and thinness some- 

 times results. Surgical removal of part of the gland may effect a cure. On 

 the other hand, any condition of sustained emotional stress is likely to 

 induce thyroid overactivity. Thyroid insufficiency {hypothyroidism) 

 causes the chemical processes of the body to proceed sluggishly; glandular, 

 muscular and mental vigor are impaired; heat production is reduced, some- 



