246 A. T. CAMERON 



that of growing animals (rabbits), decreasing the weight of adults, and 

 producing definite hypertrophy of specific organs. 



The petroleum ether-soluble portion of beef thyroids (from several 

 hundred animals) consisting chiefly of fat, averages 4.2 per cent of the 

 fresh gland (containing 75.5 per cent of water) and of this 0.13 per cent 

 consists of phosphatides, calculated as lecithin (Fenger (e), 1916). Thy- 

 roid tissue contains no more phosphatides than ordinary muscle fiber, in 

 marked contrast to the other ductless glands which all contain much larger 

 amounts. Fenger considers that this indicates that lipoids play no impor- 

 tant part in the internal chemistry of the thyroid; evidently Iscovesco's 

 results require confirmation. 



Fenger's (a) earlier papers indicate considerable variation in the fat 

 content of individual glands. There is a steady increase in the growing 

 animal, in cattle thyroids from 1.1 per cent for 3-months fetuses to 8 per 

 cent for adult cattle (1912). Bulls show a smaller amount (7 per cent) 

 than steers (10.7 per cent), and pregnancy produces no definite effect 

 (9 and 9.3 per cent, respectively, for pregnant and non-pregnant cows) 

 (1914). 



Proteins. A summary of earlier work is given by Bubnow (1883) 

 and by Oswald (&) (1899). Only two definite proteins have been isolated 

 from the gland, iodothyroglolulin, and a rmcleoglobulin (Oswald). This 

 part of the subject will be reviewed in connection with the iodin compound 

 of the gland. 



Enzymes. Thyroid tissue contains a lipase, a catalase, and is rela- 

 tively rich in nuclease. The Hpolytic capacity of the thyroid gland is 

 equal to that of the spleen and testes, and only inferior to that of the liver 

 and pancreas. The lipasc acts strongly on esters of the lower fatty acids, 

 less strongly on natural fats, and that from thyroids of carnivora is more 

 active than the corresponding preparation from herbivora. It is readily 

 extracted by water, but only to a smaller extent by giycerol (Yoishchen- 

 ko (a) (&) (c), 1910, 1911). An oxidase is present (Goldenberg). 



The Bearing of the General Biochemistry of the Halogens on Their 

 Presence in the Thyroid Gland. Excluding certain of the earlier analyt- 

 ical methods, by which, through impurity in chemicals or inaccuracy of 

 technique, iodin was found universally distributed, until recently the 

 methods employed led to minimal values, and small amounts of iodin fre- 

 quently escaped detection. From this cause especially arose the finding 

 that iodin, though generally, was not invariably present in normal thyroid 

 tissue. At present, three accurate methods are available, those of Bourcet 

 (a) (1899), Hunter (.) (li)10), and Kendall (a) (1914). The first per- 

 mits the measurement of 0.00003 per cent of iodin with accuracy, but is 

 tedious and requires large amounts of material. Hunter's and Kendall's 

 methods, with 0.5 gram of material, detect the presence of 0.001 per cent 

 of iodin ; the latter gives greater certainty of a negative result in absence of 



