168 IODINE AND THE THYROID. IV 



larvie of any single culture during the course of the experiment was 

 not attempted. Anuran larvae apparently do not swallow much 

 water, but are constantly absorbing it through the skin and eliminat- 

 ing it through the kidneys, thus a constant stream of water flows 

 through the organism. It is surprising how much water a 6 mm, 

 tadpole will absorb in 24 hours. Recently the writer^ extirpated 

 the kidneys of tadpoles, eliminating the excretory function. The 

 result was a generalized body edema of enormous proportions due 

 to water absorption. It is very unlikely that inorganic iodine will 

 be absorbed by the larvae at the same rate as water. 



Iodine has a much wider distribution in nature than is commonly 

 supposed, and is not confined solely to marine waters and organisms, 

 and the thyroid glands of vertebrates. This halogen in some form 

 or other, and in small quantities, is present in most surface water, and 

 practically all organic matter, provided a fair sized sample is analyzed. 

 It is surprising how many common foodstuffs contain traces of iodine. 

 The amounts are of course very small, and this fact has been the chief 

 hindrance in the way of recognizing iodine as of common occurrence, 

 for it is only within recent years that a method sufficiently delicate 

 to detect very minute traces of this substance has been devised. 

 With further refinement of technique it is safe to assume that iodine 

 will be found to have a far wider distribution in nature, and to play a 

 greater functional part in organisms than is at present conceded. 



In marine organisms, both animal and plant, iodine is usually found 

 in some form, and certain animals like coral are said to have a specific 

 iodine metabolism. Among land vertebrates, iodine is not only found 

 in the thyroid, but normally occurs in the blood and tissues. For in- 

 stance, KendalP finds that the average iodine content of calves' blood 

 is approximately 0.015 mg. per 100 cc. of blood. The am.ount in the 

 tissues is somewhat greater, and in the liver is still greater than in 

 the tissues. Other investigators have at various times reported the 

 presence of iodine in the ovaries, adrenals, spleen, and salivary glands. 

 The thyroids of infants a few weeks after birth are said to contain 

 iodine, hence it is not improbable that human milk contains traces 

 of this substance. 



5 Swingle, W. W., /. Gen. Physiol., 1918-19, i, 509. McClure, C. F. W., ibid., 261. 

 « Kendall, E. C, Am. J. Physiol., 1919, xlix, 136. 



