A histological study was made on the anterior pituitaries from thirty-three mice in various stages of lactation. The data showed that the pregnancy changes previously reported were maintained while lactation continued.
1) Capillary hyperaemia and sinusoidal enlargement appeared markedly.
2)Acidophile cells with a somewhat dark nucleus, a negative image of Golgi's apparatus, moderate amounts of cytoplasmic granules and basophilic filamentous materials in the cytoplasm were observed numerously.
3) The majority of basophile cells possessed generally a light nucleus, a negative image of Golgi's apparatus and sparse granulation.
4) Chromophobe cells containing a somewhat dark nucleus, a negative image of Golgi's apparatus and abundant, basophilic filamentous materials, were seen numerously. The occurrence of such cells was as frequent as, or more frequent than during pregnancy.