192 



BIOCHEMICALLY IMPORTANT MINERAL ELEMENTS 



compounds needed for their tissue structures and metabolism. Animals, 

 on the other hand, must be supplied with several preformed sulfur-con- 

 taining organic substances. These include methionine, thiamine, biotin, 

 and possibly others. 



Glutathione, a tripeptide of glutamic acid, cystine, and glycine, is 

 apparently universally present in living tissues, and by virtue of the 

 ability of the cystine constituent to change from the oxidized to the 

 reduced state, cysteine, and vice versa, the compound may function in the 

 oxidation-reduction processes of the tissues. 



Chlorine. Chlorine, in the form' of hydrochloric acid, imparts to the 

 gastric juice the proper acidity for the reaction of the digestive enzymes 

 found therein. Only a very few organic chlorine compounds have been 

 discovered in nature. One example is Chloromycetin, an antibiotic. 

 However, thousands of organic chlorine compounds have been produced 

 synthetically, and many have important industrial uses. 



The chlorine required by animals and human beings is supplied almost 

 exclusively by common salt. So much salt is ordinarily consumed that 

 the need for chlorine is amply filled. 



Iodine. This element is essential to the proper development and 

 functioning of the thyroid gland. A lack of iodine results in an enlarge- 

 ment of the thyroid, a condition known as simple goiter. McLendon 

 made an extensive study of the distribution of iodine in food and water. 

 He showed that in the areas where the iodine content of the materials 

 was low, simple goiter was prevalent. In some regions, over 70 per cent 

 of the girls of high school age had goiter. It might almost be said that 

 goiters were as common there, and as lightly regarded, as freckles. 

 Prophylactic measures — use of iodized salt, addition of iodides to drink- 

 ing water, distribution of iodine tablets to school children — are now 

 being adopted in many parts of the United States and are rapidly de- 

 creasing the incidence of this disfiginung disease. The ocean is the great 

 source of iodine and its derivatives. Sea foods and foods grown near 

 the sea commonly contain relatively large amounts, whereas foods coming 

 from far inland are low in iodine. 



A low iodine content in plants and water affects, not only human 

 beings, but also farm animals. Swine, sheep, and cattle develop en- 

 larged thyroid glands. The young may be born with little or no hair, and, 

 if alive, usually die shortly after birth. 



It is estimated that the normal human adult requires from 0.15 to 

 0.30 mg. of iodine daily. Fortunately, the body is able to store this 

 element quite readily, and the administration of iodide for two to four 

 weeks twice yearly is effective in preventing the development of simple 

 goiter. Iodized salt, which also is employed as a prophylactic measure, 

 normally contains 0.015 per cent of iodine. 



