.THE BIOCHEMISTEY OF THE THYEOID GLAND 245 

 The whole subject will be treated at greater length subsequently ; it may 

 be stated here that iodin is an invariable constituent of normal thyroid 

 tissue in all vertebrates? the observed extremes being 0.01 and 1.16 per 

 cent for dried tissue; other mammalian tissue never contains amounts 

 above the order of 0.001 per cent. 

 Ash. The ash in beef thyroids is just over 4 per cent for dry tissue ; 

 1.2 per cent for the fresh gland (Fenger, 1914). 

 Compounds Present in the Normal Thyroid Gland. Water. The 

 ratio of weight of fresh to dry tissue varies between the limits 3 : 1 and 

 6 : 1 (66 to 85 per cent water). The variations appear to depend to some 

 extent on species and to a greater extent on age. Sex does not appear to 

 exercise an appreciable influence, but castration lowers the water content. 

 The table on page 249 illustrates most of these conclusions. The effect of 

 age is shown by the following percentage figures for cattle: 3-months 

 fetuses, 84.1 ; 7-8-months fetuses, 82.3 ; 6 to 8-weeks calves, 74.3 ; adults, 

 72.6 (Fenger, 1912). Seidell and Fenger's (&) (1913) figures show a 

 seasonal variation in water content, the percentage being less in sum- 

 mer. 



Intermediate or End Products of Metabolism. Marshall and Davis 

 found 0.03 and 0.037 per cent of urea in the fresh thyroid tissue of two 

 dogs, this being approximately the amount present in all the tissues of the 

 body with the exception of the urinary apparatus. Yon Gorup-Besanez 

 (1856) noted the presence of lactic acid, which was confirmed by Bub- 

 now, Moscatelli, and Hutchison. 



Cholin is present in the thyroid (Blanchetiere and Chevalier, 1909 ; 

 Lohmann, 1911) as in most of the other tissues of the body. Lohmann 

 also extracted a crystalline substance which he suggested was 8-amino- 

 valerianic acid. 



Yon Gorup-Besanez found leucin, volatile fatty acids, and hypoxanthin. 

 W. Kiihne (1868) found in addition xanthin and succinic acid. Bubnow 

 and Hutchison confirmed the presence of xanthin and hypoxanthin, and 

 found in addition creatinin. 



These compounds are all normally present in the different body 

 tissues. 



Carbohydrates. Blumenthal (1893) obtained an osazone with m.p. 

 153C., which he concluded was a pentosazone. Grund (1902) stated 

 that dried beef thyroids contain 0.5 per cent of bound pentose. Glycogen 

 is present (Marie Ramberg and de Kieselbach) ; the thyroid contains an 

 average of 0.27 per cent, an amount similar to that in the adrenal 

 (Maraiion). 



Fats and Lipoids. Iscovesco (1913) isolated a number of different 

 lipoids from sheep's thyroid, amounting to a maximum of 15 per cent of 

 the dried gland. One of these, soluble in petroleum ether, and insoluble 

 in acetone, is stated to have marked effects on general growth, stimulating 



