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SUMMARY 1. A method has been devised for obtaining repeated biopsy samples from the mammaryglands of sows, and by its use the histological changes associated with farrowing have been studied. 2. Before farrowing, the alveoli were at first small and filled with a hyaline eosinophilic secretion. Progressive distension of the alveoli followed, accompanied by a gradual replacement of the eosinophilic material by basophilic secretion and the onset of fat secretion. At farrowing the alveoli were contracted and their contents evacuated. 3. Acute involutional changes seen in the engorged glands of early-weaned animals, or animals that were suckled with one teat occluded, were characterized by solidification of the alveoli, swollen degenerating epithelial cells and, later, stromal proliferation. Little alveolar structure remained after 8 days. 4. Descriptions are given of three main types of mammary defect that were detected histologically in clinical cases of agalactia. 5. In experiments on milk ejection, recorded manometrically, the dose-response relation to injected oxytocin was determined. Two out of three sows responded to 10 mu. and maximal responses were obtained with doses of 200–500 mu. 6. The occurrence of myoepithelial cells in the sow's mammary gland has been demonstrated by the alkaline phosphatase technique.
Cross et al. (Thu,) studied this question.