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FIG. 12. Shows the detailed analysis of the [mitosis at the upper part of [fig. 20, Plate 7, Second Scientific Report, 1905. It illustrates the mode of separation of daughter chromosomes with unequal limbs, as represented diagrammatically in fig. 11. Transplanted carcinoma of mcuse. × 3000/1. FIG. 13.-Microphotograph (untouched) of "monaster" mitosis from squamous-celled carcinoma of the tongue (man). Shows ring and U-shaped chromosomes. × 1000/1.

FIG. 14.-Analysis of same section as fig. 13. Partial separation of the daughter chromosmoes accounts for the presence of rings and U-shaped chromosomes No centrosomes or achromatic figure visible. × 3000/1.

FIG. 15.-Remainder of same cell in next section. Shows large number of chromosomes of ring and U-shape, along with others in which the widely separated daughter-rods are parallel to each other. 3000/1.

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FIGS. 1-3.-Mouse

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: Three views of a mouse with spontaneous mammary carcinoma from right and left sides, and from back after reflection of the skin. See chart, fig. 45, p. 103.

SPONTANEOUS CANCER IN THE MOUSE; HISTOLOGY, METASTASIS, TRANSPLANTABILITY, AND THE RELATIONS OF MALIGNANT NEW GROWTHS ΤΟ SPONTANEOUSLY AFFECTED ANIMALS.

By J. A. MURRAY, M.B., B.Sc.

AMONG the tumours of mammals a special interest attaches to the new growths of the mouse and rat, because of their suitability for experimental study. The number of these tumours which have been examined with care is now enormously greater than it was even five years ago, after Jensen's and Borrel's work and the investigations of the Imperial Cancer Research awakened renewed interest in the subject first touched upon by Hanau and Morau nearly a decade before. Thus it comes about that the material for a sound classification of the new growths of these small animals is not only fairly extensive, but is also much more varied than it was a few years ago. The confidence felt and expressed by those personally engaged in the experimental study of cancer on this material, that the essential features of cancer as already known and recognised in the new growths of man and other mammals, could be studied in miniature in the mouse with the additional advantage of experiment, is thoroughly justified by later developments.

It is no longer rational, or possible, to oppose a destructive criticism based on a knowledge of human cancer alone, to the results of the study of spontaneous and propagated cancer of animals. One by one the objections which have been raised have been met and refuted by direct observation. Thus the absence of metastases in the case of Jensen's primary tumour and in the inoculated animals, was shown by Haaland (Ann. Inst. Past. 1905), Bashford and Murray (Scient. Rep. 1905), not

to be constant-in fact they were commonly present after an interval of two months. The frequency with which the metastases remained as emboli in the pulmonary artery without invading the lung was regarded as another difference from cancer in man, although malignant infiltration of the lung was a conspicuous feature of the metastases we figured in the lungs in 1905. Then the ground was shifted to the growth of the tumours arising at the site of inoculation, and their encapsuled appearance was adduced as again inconsistent with the diagnosis of malignant new growth. This in turn was disproved by the demonstration of infiltrative growth in the gut-wall and diaphragm (Bashford, Murray and Cramer, 1905). v. Hanseman and after him Lazarus - Barlow contended vehemently that most of the the tumours of the mammary region of the mouse were endotheliomata and not carcinomata, following the views expressed by Eberth. Apolant (1906) and, with Bashford, we (Lancet ' 1907) showed the improbability of this view.

The best reply, however, to all these criticisms has been afforded by the gradual accumulation of a number of growths from other regions in the mouse in which the histological diagnosis is unequivocal, and quite distinct from that of the ordinary mammary growths, which have led to so much dubiety in the minds of advocates for a continuation of histological and pathological study in man without resort to experiments on animals. The mere fact that mice suffer from cancer of other organs of the body and that in those other situations the growths extend in the same way as do those met with in other animals and in man, diminishes the importance of the apparently exceptional characters of the majority of the mammary growths. Furthermore the tumours of the mammary region now include primary growths of unusual type in this animal, such as the squamous-celled carcinoma and the angioma and chondro-osteo-sarcoma described at pp. 78 and 81. It would indeed be remarkable if true carcinoma of the mamma did not occur in the mouse, an animal in which primary carcinoma of the lung (Livingood, Haaland and Tyzzer), the floor of the mouth (Borrel, Haaland), and the small intestine (Bashford, Murray, Cramer, and Twort) have been recorded. Therefore we shall preface the following account of the malignant new growths of the mammary region by giving a description of a number of malignant new growths of the mouse which do not belong to that group. From the standpoint of experiments it is also of moment to know that they are not carried out on an animal with a peculiar idiosyncrasy to a single form of cancer, viz., of the mamma as is too frequently asserted.

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