The composition of the crop milk of pigeons.

PIGEON squabs are hatched in the undeveloped state but grow very rapidly during the first few days after hatching. During this period they are fed on a special secretion formed in the crop ofthe parent birds. This secretion, commonly called "pigeon's milk", is a white, slimy, caseous material formed by the desquamation of epithelial cells and may be regarded as an example of a sacrifice of cell structure in the parent for the nutrition of the young. The endocrine control of its formation has been investigated by Riddle et al. [1932]. Its general composition and nutritive properties have been studied by Reed et al. [1932] and by Dabrovska [1932]. The former workers found the material to contain dry matter 35 7 %, with protein 52-7, fat 35-6 and ash 4*5% of the dry matter; Dabrovska found dry matter 23-3 %, and protein 57 4, fat 34-2 and ash 6-5% of the dry matter. The material did not contain carbohydrates. In the present work, the compositions of four samples, pooled from 115 birds (three from 30 birds each, one from 25), have been investigated in detail. The birds had been used for prolactin assays, in which activity was measured by the wet weight of the crop glands. The gland contents were separated and made available for analysis as soon as possible after killing the birds.