THE THYROTROPIC HORMONE 



Hal cells — were first investigated by Aron and Loeb^' and 

 have been extensively used as a means of assay. According 

 to Wilcke (1935), fixation is of great importance, if an at- 

 tempt is made to grade the histologic effects by the plan of 

 Heyl and Laqueur; Wilcke recommended 10 per cent forma- 

 lin as a fixative. The production of thyroid hypertrophy as a 

 means of assay (Rowlands and Parkes) is more objective but 

 requires much larger doses of hormone. There is no confirma- 

 tory evidence to support the contention of Heyl and Laqueur 

 that a different principle is responsible for hypertrophy. 



Smelser (1937) recommended the use of day-old White Leg- 

 horn chicks. His practice was to divide the total dose into 

 five daily injections and to perform the necropsy 24 hours 

 after the last injection, when the thyroid lobes were dissected 

 out under a binocular microscope. The method was found to 

 be more sensitive than a similar technic applied in guinea pigs. 



Other methods which may be sensitive are either incon- 

 venient or are difficult to evaluate. For example, the decrease 

 in the total amount of iodine in the thyroid of chicks or 

 guinea pigs as a result of thyroid stimulation is a method sug- 

 gested by Cuyler, Stimmel, and McCuUagh (1936) and Stim- 

 mel, McCullagh, and Picha (1936). Atwell (1935) recom- 

 mended the hypophysectomized tadpole as a very sensitive 

 biological indicator; the prominent change which occurs if 

 thyrotropic (or thyroid) extract is administered is meta- 

 morphosis. Collip and his collaborators have frequently de- 

 tected the presence of thyrotropic hormone by its calorigenic 

 action in hypophysectomized rats. 



The chemistry of thyrotropic hormone. — Thyrotropic hor- 

 mone is available only as an impure extract. It is a heat- 

 sensitive substance which, like other anterior pituitary hor- 

 mones, appears to belong to the group of proteins. Readers 

 interested in a new report on the preparation of extract are 

 referred to the article of Lambie and Trikojus (1937). There 



''The following are late reports by these authors: Kippen and Loeb (1935) 

 and Aron (1936). 



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