Chemical Messengers 81 



mental faculties. It was found by Murray in 1891, that this condition 

 could be relieved by feeding sheep's thyroid. The active substance in 

 the thyroid extracts was isolated by E. C. Kendall in 1916, and in 

 the course of time its structure was established, and it was finally 

 synthesized in 1927 by Barger and Harington. It is a comparatively 

 simple substance, a compound of iodine and a common amino-acid, 

 tyrosine. Because of this, the thyroid gland is the reservoir of most 

 of the iodine in the body. If the water supply is deficient in iodine, as 

 happens in some limestone districts, the thyroid is unable to make 

 enough thyroxine and it increases in size in an effort to make up the 

 deficiency. This produces goitre, once a common disease in mountain 



areas. 



Thyroxine is concerned with the oxidation of fats and proteins. 

 When it is absent, the body does not develop properly, giving rise to 

 cretinism. Over-activity of the thyroid causes protuberant eyes and 

 a kind of feverish activity. It is necessary for the metamorphosis of 

 the lower animals. With the thyroid gland removed, tadpoles cannot 

 metamorphose into frogs. On the other hand, when small quantities 

 of thyroxine are added to the water, tadpoles will change prematurely 

 into miniature frogs. It is intimately connected with the secretion of 

 milk. Injection of thyroxine into cows markedly increases both their 

 milk and their fat production — at least temporarily; and it has been 

 found that feeding iodinated proteins, which probably help the cow 

 to make thyroxine, has a similar effect. 



The pancreas is another organ which produces substances necessary 

 for health, as well as the digestive enzymes it pours into the intestine. 

 If it is damaged or removed, serious bodily changes occur, especially 

 an inability to oxidize sugar, which then accumulates in the blood. 

 This is what happens in the disease diabetes, which is due to an 

 impaired action of the pancreas. It was found that this condition was 

 relieved by extracts of pancreas from animals, and in 1921 Banting 

 and Best in Toronto isolated from the pancreas a protein called 

 insulin. Actually it is present in separate parts of the pancreas, distinct 

 from the enzyme-producing parts, known as the islets of Langerhans. 

 Only a fraction of a milligram of insulin is required each day by a 

 healthy person, and diabetics can be kept going indefinitely by in- 

 jections of ox or swine insulin. 



One of the first to benefit from insulin was Dr R. D. Lawrence, 

 who has since become one of the foremost authorities on diabetes. 

 In 1922 during an operation, a bone splinter flew into and injured his 

 right eye. The wound turned septic and he became very ill. His illness 

 was eventually diagnosed as diabetes, and he was considered a hope- 

 less case. He went to Florence to spend what time he had left and 



