. 



HORMONE FACTORS IN GROWTH AND DEVELOPMENT 201 



sexual maturity and in man is found in a functional condition as late as 60 

 years or longer after birth. Klose had given especial weight to the changes 

 of the bones which in the main were the effects of disturbed calcification 

 due to lack of precipitated calcium in the body and were identified by 

 Matti as rickets. Liesegang, one of Klose's collaborators, on the basis of 

 these findings developed a theory of thymus function, according to which 

 the thymus was considered the center of the nuclein synthesis; after 

 removal of the thymus, in consequence of the disturbed nuclein synthesis, 

 a phosphoric or nucleic acid acidosis develops in the organism, as Liesegang 

 assumed, and by keeping the calcium dissolved prevents proper deposition 

 of it in the bones. Dustin, who, upon embryological grounds, also holds 

 the view that the thymus is the center of nuclein synthesis, recently has 

 expressed himself more definitely as to the exact mechanism of the thymus 

 function in growth and differentiation. Einding that a large thyroid 

 always coincides with a small thymus and vice versa in the same indi- 

 vidual, he thinks that growth is controlled by the thymus only indi- 

 rectly by the aid of the thyroid, the latter organ being the cause of in- 

 creased organic differentiation, tissue repairs, growth and development 

 and mobilizing from the thymus the nuclein needed for these proc- 

 esses. 



Well in accord with Klose's findings of a disturbed calcium metabol- 

 ism, in the .absence of the thymus, was an observation made by Soli; 

 when he removed the thymus from hens, eggs were laid which did not 

 possess a shell ; upon feeding calcium to the thymectomized hens, the shells 

 were again formed. 



As to the role of the thymus in sexual development Paton, Adler (&) 

 and Hewer believed that the thymus inhibits development of the testes, for 

 Paton in guinea pigs and Adler in tadpoles had found that thymectomy 

 results in an accelerated development of the testes as far as weight and 

 size are concerned, arid Miss Hewer found that feeding thymus retards 

 the development of the testes. The results as to the role of the thymus in 

 the development of the testes were, however, not uniform, for Soli pub- 

 lished several articles in which he reported that thymectomy in cocks, 

 guinea pigs and rabbits delayed the development of the testes. 



The opinion that the thymus gland stimulates bodily growth received 

 particularly effective support when Gudernatsch in 1912 and Romeis in 

 1913 began to publish their papers on the results of feeding thymus gland 

 to the tadpoles of frogs and toads. If young tadpoles were fed on thymus, 

 they began to grow more rapidly than the control larvse and some of 

 them reached enormous sizes. But while in these experiments the thymus 

 favored growth, it frequently retarded or even inhibited completely the 

 development of the larvse. Since the same authors had observed that 

 feeding thyroid to the tadpoles had just the opposite effect, it was believed 

 from this time on that the function of the thymus is antagonistic to that 



