188 E. UHLENHUTH 



to the toxic action of iodin than tadpoles. It is possible to keep salamander 

 larva? in sofutions of 5 drops of 1/20 m. iodin in 1000 c.c. and feed them 

 while they are in this solution on large crystals of iodin without pro- 

 ducing any toxic effects. If the animals are kept in 8 drops of 1/20 m. 

 iodin and 1000 c.c. water, the movements of the animals become con- 

 vulsive, though it would be possible to go still higher without killing them ; 

 feeding too large crystals of iodin results in death. As to the effect of 

 iodin upon metamorphosis in salamanders, it is of no difference what 

 concentration is used, iodin has no effect on development. Neither does 

 it accelerate the growth of the legs, nor does it in the least stimulate meta- 

 morphosis. Since keeping the animals in weak solutions of iodothyrin 

 results in almost immediate metamorphosis, it seems that iodin is not 

 the chief factor that causes the specific action of the thyroid hormone; 

 apparently the effect of iodin in tadpoles is merely due to some peculiari- 

 ties of the frog larvas as indicated above. 



In conclusion it should be pointed out that thyroid substance may result 

 in an acceleration of growth and development even in organisms that do 

 not possess anything like a thyroid gland. Kunkel found that the larvaB 

 of the common flesh fly develop more quickly if fed on thyroid substance 

 and various observers (Shumway, Nowikoff) observed that in protozoa 

 the rate of division can be increased markedly if thyroid substance is 

 added to the culture medium. 



The Relation of the Hypophysis Cerebri to Growth 

 and Development 



Aside from the thyroid gland the hypophysis cerebri is probably the 

 most important endocrin gland in the control of the processes of growth 

 and development. Since Pierre Marie discovered that in acromegaly the 

 hypophysis shows important changes of its histological structure, atten- 

 tion has been called repeatedly to the growth controlling activity of the 

 pituitary body. On the basis of. our present knowledge it seems safe to 

 say that the hypophysis elaborates a specific substance, which in some 

 way as yet not well understood, accelerates growth, development of the 

 sexual characters and, in certain groups of organisms, bodily development 

 in general. 



Introduction. Functions of Different Parts of the Hypophysis. 

 Since the pituitary body is composed of several distinct portions the 

 activities of which have early been recognized to be essentially different 

 (Howell, Magnus and Schafer) the question arose as to what part of the 

 organ is involved in the control of growth and development. The feeding 

 experiments (Schafer, Smith (c) (e], Goetsch (a), Uhlenhuth's unpub- 

 lished experiments) as well as the extirpation experiments show conclu- 



