EDUARD UHLENHUTH 363 



urally grow best. Feeding of calf thymus or posterior lobe of hypophy- 

 sis of cattle does not induce any growth equal to that of worm-fed 

 animals. In the feeding of salamander larvae I have used many differ- 

 ent substances (frog muscle, beef muscle, lymph gland, parathyroids, 

 thymus, spleen, cheese, milk) with and without the addition of normal 

 food; it is certain that in larvae no other diet can produce a rate of 

 growth higher than that produced by earthworms. But, of course, 

 the metabolic processes involved in growth may be quite different 

 for the larvae and the metamorphosed animals. 



On the other hand, if we look at the curves of the various series, it 

 is noticeable that the curves for the worm-fed animals are very much 

 like the normal growth curves of most other animals whose growth 

 has been studied carefully. In particular they show the gradual flat- 

 tening out of the growth curves of warm blooded animals. The 

 curves of the anterior lobe-fed animals, especially those of Ambystoma 

 opacum (Fig. 2), with their sudden rise above the flat level of the 

 normal curve, differ from this general normal type. 



Although at present we must postpone more definite conclusions, 

 it seems at least probable that the rate of growth of the animals fed 

 exclusively on anterior lobe is the result of a specific growth-promoting 

 hormone contained in the anterior lobe of the hypophysis. 



It is beyond doubt that the size of the hypophysis-fed animals 

 exceeds the "maximum" size of the species. The animals fed on ante- 

 rior lobe are true giants. The hormone of the anterior lobe is not only 

 able to accelerate growth, but also — and this is of far greater impor- 

 tance — possesses the property of maintaining growth when the nor- 

 mal size of the species has been reached. The production of experi- 

 mental gigantism by means of feeding anterior lobe proves that this 

 organ contains actually a specific substance which can overcome the 

 obstacles which are responsible for the discontinuation of growth 

 when the normal size is reached. 



These experiments do not give any clue as to whether the cells of 

 the body are directly affected by the hormone or whether this hormone 

 acts by the intermediation of another organ. In view of the results 

 obtained with single cells, it is probable that the cells are not directly 

 affected by the anterior lobe hormone. It was found by Shumway, by 



