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terest gradually faded out, leaving the impression that the thymus 

 supplied some "nutritional factor" rather than a growth hormone. 

 The hormonal theory was revived more recently in experiments of 

 Harms, who found general atrophy in salamander larvae after 

 extirpation of the thymus, atrophy which could be prevented by 

 thymus transplants. Gudernatsch also showed that the feeding of 

 thyroid substance had an action opposite to that of the thymus. 

 While the latter retarded metamorphosis and promoted growth, 

 the thyroid promoted metamorphosis and inhibited growth. While 

 giant tadpoles were produced by the former, dwarf frogs were 

 produced by the latter, suggesting some sort of an antagonism 

 between the two. 



There is no need for the author to sum up the literature of the 

 subject, this having been ably done by Gudernatsch and Hammar. 

 One could almost say that all possibilities have been expressed 

 about the function of the thymus, the integral being zero. 



Techniques of isolation have been perfected so much during the 

 last decade that, as a rule, the isolation of a substance, in itself, 

 does not constitute a major problem. What the isolation depends 

 on is a test for the unknown substance which allows us to estimate 

 its quantity in different fractions in the course of manipulations. 

 The difficulty, in this case, is that we have to find a test for some- 

 thing that has to be found by that test. This is a circle which, 

 somehow, has to be broken. 



The author made an abortive attempt in this direction reasoning 

 in the following way: small quantities of biologically active normal 

 constituents of the body usually produce effects in the animal only 

 if there was a deficienc}^ before. Vitamins, for instance, produce 

 striking effects only in an avitaminostic condition. Should myo- 

 tonia be due to a lack of the hypothetic thymus hormone, then 

 myotonic goats would be the test object for the hormone par 

 excellence. So four female myotonic goats were trained according 

 to G. L. Brown for the measurement of their running time. Then 

 they received daily an injection of a thymus extract which con- 



