In the investigation of tumors in mice, attention has been, for the most part, directed to those which develop in the subcutaneous tissue. It is possible that internal tumors often occur unnoticed. In this series the tumors of the lung are most frequent.

Primary, papillary, cyst-adenomata of the lung have been found in eleven cases. All these tumors conform to one type, and consist of cuboidal or columnar epithelium covering irregular folds and processes of connective tissue. No mitotic figures have been found in the epithelium of these tumors, so that it is evident that they are not rapidly growing. Most of these tumors were very minute and in several instances, when they occurred with other primary tumors, they were mistaken for metastases until examined histologically. In one case a tumor of this type attained such size that it filled about one third of the thorax. In two other cases tumors were found growing into the bronchi. These tumors occur in both male and female, and appear to be about equally frequent in the inoculated and non-inoculated mice. The largest of the lung tumors was inoculated into five mice, but failed to develop further.

Minute adenomata of the kidney were found in two cases.

A rapidly growing lympho-sarcoma, which occurred in an old female mouse, was inoculated into seventeen mice with negative results.

Tumors of the mammary gland have developed in three old female mice, and in each case the lymphatics were invaded by the growth. In the first case the primary tumor presents, in addition to simple adenoma, transitions from this to an actively growing carcinoma. Another adeno-carcinoma of the mammary gland occurred in a waltzing mouse. The tumor is peculiar in that groups of the epithelial cells become vacuolated, and resemble very closely the sebaceous glands of the skin.

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Papillary Adenocarcinoma of the Extrahepatic Bile Duct in a Holstein Cow

A series of spontaneous tumors in mice