The Biochemistry of the Thyroid 



Gland 



A. T. CAMEKOE' 



WINNIPEG 



Introduction 



From a biochemical standpoint the chief problems concerned with the 

 thyroid gland are the chemical nature of the compounds present in the 

 internal secretion elaborated by the gland, the mechanism of their manu- 

 facture, and their chemical effect. Of the first and third of these prob- 

 lems we are commencing to know a little ; it is only possible to correlate a 

 few facts which may perhaps be concerned with the second problem. 



The outstanding feature which differentiates the thyroid gland from 

 all other tissues in vertebrates is the constant presence of measurable 

 amounts of the element iodin in normal individuals. Consequently any 

 discussion of the nature and function of the secretion must consider the 

 importance of iodin as an indispensable constituent, and contrast the rela- 

 tive effects of other iodin-containing substances ; this leads naturally to a 

 consideration of the relative positions of iodin, biochemically, compared 

 with the other halogens, especially as all four are stated to be present in 

 the gland. 



Recently, considerable advance has been made in our knowledge of the 

 form of combination of iodin in thyroid tissue ; a crystallizable iodin com- 

 pound has been isolated from the cleavage products. It will be necessary 

 to refer to this important advance in some detail. 



Finally, a brief account will be given of our present knowledge of the 

 chemical variations accompanying pathological conditions of the gland. 



The Elementary Composition of the Normal Thyroid Gland. The 

 following elements have been reported present : C, H, O, E", S, P, E"a, K, 

 Ca, Mg, Si, As, F, Cl, Br, I. There does not appear to be any record of 

 analyses of the first three of these in whole thyroid tissue. Zunz (a) (&) 

 (1919) found for dry fat -free tissue of normal men killed in war a nitro- 

 gen content varying from 12.46 to 14.82 per cent, the mean value being 

 13.8 per cent (corresponding to about 4 per cent for fresh tissue). 



Morgenstern (1912) examined 50 human thyroids for Ca, Mg, S, P, 

 and I. Twenty-two were pathological; ten of these contained Mg. It 



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