10 THE ROYAL SOCIETY OF CANADA 



Systematic analyses of all the tissues of the rabbit and the dog 

 gave negative results except for the thyroid. 



The thymus has been examined for a number of species (pigeon, 

 brown rat, albino rat, guinea-pig, rabbit, cat, dog, man) with consistent 

 negative results, in agreement with previous results of Cunningham 1 

 and Mendel. 2 



Examination of these fresh data, and comparison of them with 

 the large number of analyses previously published by other observers, 

 lead to the following conclusions: — 



(1) Iodine is an almost invariable constituent of all organisms, 

 plant and animal, the amount present depending on the diet and 

 medium of the organism. 



(2) With greater development there is greater specificity of 

 the tissue concerned in storing iodine, until in vertebrates no tissue 

 except thyroid contains appreciable quantities. 



(3) All normal thyroids contain iodine, the amount varying 

 with the diet, and between the limits 0-01 and 1-1 per cent, (dry 

 tissue). 



(4) Besides the skeletal tissues of Sponges and Corals, three 

 additional types of tissue have been found, which contain iodine 

 in quantities comparable with those in thyroids, the horny tubes of 

 Eunicid worms, the external cutaneous tissue of the "foot" of the 

 horse-clam, and the test of a tunicate. 



I wish to acknowledge my grateful indebtedness to Dr. Maclean 

 Fraser, the Curator of the Nanaimo Biological Station, for his uniform 

 kindness in assisting me in the work of collection and identification 

 of the material described in this paper, to thank Mr. F. S. Collins 

 for kindly identifying a number of algae for me, and to thank Pro- 

 fessors Swale, Vincent and Buller for their interest and encouragement 

 in the course of the work. 



The expenses incurred in the collection and preservation of the 

 Nanaimo material were defrayed by grants from the Biological 

 Board of the Dominion. The remaining expenses have been defrayed 

 by grants through the Ducltess Glands Committee of the British 

 Association for the Advancement of Science, and (through Professor 

 Vincent) from the Royal Society of London. 



The work forms part of researches carried out under the direction 

 of the Ductless Glands Committee of t he British Association. 



1 /. Exp. med., 3, 231, footnote, 1898. 



2 Amer. J. physiol., 3, 285, 1900. 



