Secretion of Crop-Milk in the Castrate Male Pigeon

Abstract
Riddle and Braucher1 showed that the cyclical extreme enlargement of two areas of the crop wall, and the resulting crop-milk formation—both well known to occur at or near the end of the brooding period in pigeons—are under control of a hormone of the anterior pituitary. Only anterior pituitary tissue or extracts were found capable of initiating these processes, but with such tissue or extracts these phenomena could be produced in birds of both sexes and at all ages. While unaware of the results of Riddle and Braucher a report was later published by Kaufman and Dabrowska2 in which the conclusion is drawn that the hormone of the testis is necessary for the normal cyclical functioning of the cropgland in the male pigeon. Kaufman and Dabrowska castrated a male pigeon which had previously secured a female mate within a group of pigeons. After the male was castrated he ceased to copulate and express ardor, but nevertheless still maintained a special interest in his former mate. This female mate continued to lay fertile eggs—thus showing that another male (or other males) were copulating with her, and was wholly or in part stimulating the growth and ovulation of the eggs which she laid. It would therefore be a matter of much surprise if the castrate male began to incubate at the time this female laid eggs; for, even an unmutilated male pigeon who has been solely responsible for stimulating egg production in his mate is sometimes 2 to 5 days out of syncrony3 with his mate in the impulse to begin to brood or sit; again, apparently normal males sometimes brood for a few days only and fail to complete the cycle. Indeed, it is of much interest that a castrate pigeon will incubate at all, and (though apparently unaware of this) Kaufman and Dabrowska have observed what seems to be the first recorded case