Abstract
OUR knowledge of the cytology of milk secretion—what structures in the large cells lining the alveoli of the mammary gland are concerned with the formation of the various milk constituents—is meagre. There is no doubt that all the milk constituents are secreted by the same type of cell; there are not separate cells secreting fat, others secreting casein, others secreting salts and so on. It is now usually agreed also that the milk-secreting cells are fairly permanent structures; that is, that milk does not originate from the breakdown and dissolution of complete cells which are renewed again and again from the basement membrane. This would entail far more mitosis and repair in cell structure than can be seen in the actual functioning gland, and would probably entail the presence in milk of fairly large amounts of substances derived from the cell nuclei, such as nucleoproteins or breakdown products of these proteins which are, in fact, only present in traces in milk. What appears to be the case is that apart from occasional breakdown and repair, the alveolar cells maintain their nuclei and general integrity throughout a large part of a lactation period.
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KAY, H. The Secretion of Milk*. Nature 156, 159–162 (1945). https://doi.org/10.1038/156159a0
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DOI: https://doi.org/10.1038/156159a0