8 THE ROYAL SOCIETY OF CANADA 



content of the gland in different species of animals (as distinct from 

 the marked individual variations which occur in the same species) 

 were attributed to this cause by Roos, 1 and the theory is usually 

 accepted that the diet of an animal is the determining factor of the 

 amount of iodine in its thyroid. Reasoning from this I was led to 

 examine the thyroids of certain elasmobranch fishes, since these 

 existing in a medium containing iodine in distinct amount, should 

 show high figures for the iodine content of the thyroid if the theory 

 were correct. I found 2 that iodine was present in marked amount, 

 and, for the female dog-fish, Scyllium canicula, obtained a value 

 higher than any previously recorded. These results suggested the 

 desirability of examining the various forms of sea-life in greater detail. 

 The examination of the iodine compounds in Sponges and Corals, 

 leading to the definite identification of 3, 5-di-iods-l-tyrosine as one of 

 the forms in which iodine is linked in organic tissue 3 and not improbably 

 in the thyroid itself, 4 indicated that further light might be thrown on 

 the problem of the form or forms in which iodine is held in living 

 tissue, by an investigation over a wider field. 



With the permission of the Biological Board of Canada I was 

 able to collect material at their Pacific Coast Station at Nanaimo, 

 B.C. I obtained a large number of specimens of different species of 

 Algae, and specimens of representative species of most of the animal 

 phyla. The selection of the latter was made more or less at # random, 

 and analysis of different tissues examined was also not systematic; 

 the investigation undertaken was more or less preliminary, with 

 the purpose of indicating the direction for further work. Complete 

 examination of the tissues of the dog fish Squalus sucklii was carried 

 out. I have employed Hunter's method throughout. 5 Since most 

 of the results of previous observers have been obtained by the use of 

 Baumann's method of analysis, 6 or of some modification of it, and 

 since there is considerable evidence that this method frequently 

 yields too small values, and does not detect small amounts, 7 it seemed 

 desirable to carry out a systematic examination of ordinary mammalian 

 tissue. I have done this for the dog and the rabbit. 



The details of the analyses will be published elsewhere, and in 

 this paper I shall only give a resume of my results. They are all 

 expressed for dry tissues (dried at 100° C. to constant weight). 



1 Zeitschr.f. physiol. Chem., 28, 40, 1899. 



2 Biochem, J., 7, 466, 1913. 



3 See for example Wheeler and Mendel, J. Biol. Chem., 7, 1, 1909; Môrner, 

 Zeitschr.f. physiol. Chem., 51, 33, 1907; 55, 77, 223, 1908. 



4 COmpare for example Oswald, ibid., 62, 432, 1909. 

 6 J. Biol. Chem., 7, 321, 1910. 



6 See Baumann and Roos, Zeitschr. f. physiol. Chem., 21, 489, 1895. 



7 I have discussed this evidence previously. See /. Biol. Chem., 16, 465, 1914. 



