Studies on Milk Secretion the Influence of Inanition by John W. Gowen and Elmer R. Tobey

Milk secretion may be looked upon as a two-step process. The first step consists in the passage of the materials for the formation of milk from the blood stream into the gland cells. In the second step these materials are organized by the gland cells into the constituents of milk, when they are then passed into the alveolar spaces of the udder. The question arises as to what may be the motivating causes which bring about these changes. The early contributions to this subject were largely those made by the histologist studying the changes which he observed in the tissue of the mammary glands. These histological observations have been markedly influenced in their interpretation by the supposed modes of secretion of two other types of glands, the sebaceous and the salivary. This work led to three major hypotheses to account for milk secretion by the mammary glands: 1. The cells of the glands break loose bodily and disintegrate'in the alveoli to form the milk solids. 2. A portion of the cells toward the alveoli become loaded with solids, are broken from their base, and disintegrate to form the constituents of milk. 3. The cells of the mammary glands secrete the materials of the milk solids without the cells breaking down. The first theory has largely been discredited because as Heidenhain (1) 2 pointed out this theory would call for a cell destruction and replacement of as high as five times the number of cells in the udder in a single day; a rate of cell replacement which was not observed.