A HORMONE FOR GESTATION 



ory's record of friendly rivalry and mutual enthusiasm. 

 Without apology, then, let these personal feelings color 

 (for so they must) the narrative of research. 



The collection of evidence begins with a scene poignant 

 enough, indeed, for a novel. In 1900 the great embryologist 

 of Breslau, Gustav Born, lay dying. Scientist to the last, 

 his mind was full of a hypothesis he knew he could not live 

 to test and which he could not bear to leave untried. To his 

 bedside, therefore, he summoned one of his former students, 

 the rising young gynecologist Ludwig Fraenkel. To him 

 Born imparted his thought that the corpus luteum is indeed 

 an organ of internal secretion, and moreover that its function 

 must be concerned with the protection of the early embryo. 

 This guess about its specific function, like Prenant's about 

 its general nature, was brilliant and novel in its day, even 

 though to us in retrospect when we consider that the corpus 

 luteum is present only when the egg is available for develop- 

 ment, such a function seems probable indeed. So it seemed 

 then to Fraenkel, whose task it was to devise the experiments 

 by which Born's conjecture could be put to rigorous test. 



He knew that in the rabbit the embryos become implanted 

 in the uterus on the 8th day after mating. They spend 3 

 days in the oviduct and then 4 days more as free blastocysts 

 in the uterus, before they become attached. To test the 

 function of the corpora lutea, Fraenkel planned to interfere 

 with the natural course of events by removing them while 

 the embryos were still unattached. The simplest way of 

 removing the corpora lutea is of course to remove both 

 ovaries, by surgical operation under an anesthetic. Since 

 this might, for all he knew, remove some other useful or 

 necessary factor, Fraenkel tried also cutting out the corpora 

 lutea alone, or burning them out with a fine cautery, of 

 course always under an anesthetic. This operation is more 

 difficult than simple removal of the ovaries. The rabbit sheds 

 many eggs at a time, up to 10 or even 12, and a correspond- 



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