The effect of salts on cell permeability as shown by studies of milk secretion

The physiology of milk secretion has been studied to some extent from the point of view of the relation of milk to the blood from which it is formed so that there is now definite evidence concerning the blood precursors of several of the milk constituents, as can be seen from the articles by Meigs (1922), Meigs and Cary (1928), and Blackwood and Stirling (1932). There is still, however, a lack of information as to the intimate processes involved in the mammary cells, leaving a wide gap in our knowledge of the whole mechanism of secretion. The following communication describes experiments which are directed towards bridging this gap, from the point of view of the regulation of the supply of precursors to the cells. For the sake of simplicity, milk can be regarded as composed of two fractions only—lipoid and non-lipoid—and, so far as is known at present, the blood precursors of these two fractions can be similarly considered. Now the supply of these precursors to the cells will depend on the cell-permeability to lipoid and non-lipoid materials respectively, and it may be assumed that, in an actively secreting gland in which the precursors are being transformed and secreted rapidly, the relative proportions of these precursors reaching the cells may influence the composition of milk in the same direction.