THE HORMONES IN PREGNANCY 



the chemical separations, but be and I found only that we 

 were dealing with a protein, after which we simply got lost in 

 this most difficult field of biological chemistry. Meanwhile my 

 genial and versatile friend Oscar Riddle of the Carnegie In- 

 stitution (Department of Genetics, at Cold Spring Harbor), 

 ably assisted by his colleague R. W. Bates, applied his all- 

 round knowledge of tissue chemistry to the task and suc- 

 ceeded in purifying the hormone to a considerable degree. He 

 called it prolactin. The complete chemical isolation and chem- 

 ical identification of this important substance is now a prob- 

 lem for the most advanced special experts in the chemistry of 

 proteins (Appendix H, note 17). 



There is a queer sequel of this discovery of prolactin, which 

 opens a vista of the long past origin of the hormones in evo- 

 lutionary history. This story has to do with pigeons' milk. 

 Not that pigeons have mammary glands ; but females of the 

 genus actually secrete into their crops a kind of milky secre- 

 tion which they regurgitate and feed to their nestlings. This 

 crop-milk is produced by special glands in the lining of the 

 crop. Dr. Riddle knows all about pigeons ; he has been study- 

 ing their physiology for years and had a fine collection of 

 them at Cold Spring Harbor. Impressed by the parallelism 

 between the formation of crop-milk and mammalian lactation, 

 he administered his extract of beef pituitaries to some of his 

 female pigeons and got proliferation of the crop glands just 

 as if they were mammary glands. This reaction is so easy to 

 produce that it is now the standard test for prolactin. The 

 strangest part is, however, yet to be told. The eggs of the 

 amphibians (frogs, toads, and salamanders for example) are 

 laid in the water and the embryos have the benefit neither of 

 nest and crop-milk nor of uterus and mammary gland. When 

 the eggs are shed by the mother, however, they are protected 

 by an envelope of jelly, laid on in the mother's oviduct. An 

 Argentine physician, already mentioned in this work. Dr. 

 In^s de Allende of Cordoba, has discovered that a hormone 



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