264 THE RATE OF GROWTH 264 



trophy or over-activity goes to the making of a giant; the Umb- 

 bones of the giant grow longer, their epiphyses get thick and clumsy, 

 and the deformity known as "acromegaly" ensues*. This has 

 become a famihar illustration of functional regulation, by some 

 glandular or "endocrinal" secretion, some enzyme or harmozone 

 as Gley called it, or hormone'f as Bayliss and Starhng called it — in 

 the particular case where the function to be regulated is growth, 

 with its consequent influence on form. But we may be sure that 

 this so-called regulation of growth is no simple and no specific thing, 

 but imphes a far-reaching and complicated influence on the bodily 

 metabohsmj. 



Some say that in large animals the pituitary is. apt to be dispro- 

 portionately large §; and the giant dinosaur Branchiosaurus, hugest 

 of land animals, is reputed to have the largest hypophyseal recess 

 (or cavity for the pituitary body) ever observed. 



The thyroid also has its part to play in growth, as Gudernatsch 

 was the first to shew||; perhaps it acts, as Uhlenhorth suggests, 

 by releasing the pituitary hormone. In a curious race of dwarf 

 frogs both thyroid and pituitary were found to be atrophied ^. When 

 tadpoles are fed on thyroid their legs grow out long before the usual 

 time; on the other hand removal of the thyroid delays metamor- 

 phosis, and the tadpoles remain tadpoles to an unusual size**. 



The great American bull-frog (R. Catesheiana) fives for two or 

 three years in tadpole form; but a diet of thyroid turns the little 

 tadpoles into bull-frogs before they are a month old If- The converse 



* Cf. E. A. Schafer, The function ofjthe pituitary body, Proc. R.S. (B), lxxxi, 

 p. 442, 1904. 



t It is not easy to dtaw a line between enzyme and vitamin, or between hormone 

 and enzyme. 



X The -physiological relations between insulin and the pituitary body might 

 seem to indicate that it is the carbohydrate metabolism which is more especially 

 concerned. Cf. (e.g.) Eric Holmes, Metabolism of the Living Tissue, 1937. 



§ Van der Horst finds this to be the case in Zalophus and in the ostrich, compared 

 with smaller seals or birds; cf. Ariens Kappers, Journ. Anat. lxiv, p. 256, 1930. 



II Gudernatsch, in Arch. f. Entw. Mech. xxxv, 1912. 



<;; Eidmann, ibid, xlix, pp. 510-537, 1921. 



** Allen, Journ. Exp. Zod. xxiv, p. 499, 1918. Cf. [int. al.) E. Uhlenhuth, 

 Experimental production of gigantism, Journ. Gen. Physiol, ill, p. 347; iv, p. 321, 

 1921-22. 



tt W. W. Swingle, Journ. Exp. Zool. xxiv, 1918; xxxvn, 1923; Journ. Gen. 

 Physiol. I, II, 1918-19; etc! 



