Studies on the heredity of cancer in mice / by J.A. Murray.

  • Murray, J. A. (John Andrew)
Date:
1914
Catalogue details

Licence: In copyright

Credit: Studies on the heredity of cancer in mice / by J.A. Murray. Source: Wellcome Collection.

    4/14 (page 68)
    separately by a consideration of family pedigrees, and the main study will be concentrated, as before, on the observations of the relative fre¬ quency of cancer in female mice in the ancestors of which cancer has occurred recently or in remote generations. In the mouse, as in the human subject, cancer arises with greater frequency in the higher age-periods, and although more than 2,000 mice have been bred in the laboratory for these observations during the past six years, no case of malignant new growth has been discovered in a female mouse less than six months old. The restriction of the inquiry to animals aged six months or more has reduced the numbers available to 800 females, among which 136 had developed malignant new growths up to October 24, 1912. Relation to Age These cancer cases are not distributed equally over the months from the sixth to the thirtieth, beyond which few mice survive. As the following table (Table I) shows, the differences in numbers of cases of cancer observed at each successive period of three months are considerable. TABLE I Age-period, in Months 6-10 -13 -16 -19 -22 -25 Over 25 Cases of cancer 13 24 36 34 12 12 5 It might appear from such a table that in the mouse the majority of the cases of cancer occurred in the first eighteen months of life and particularly from the sixth to the nineteenth month, and that thereafter the disease was rarer. Such a statement would be entirely misleading and conceals important information, since no account is taken of the number of animals in which these cases have arisen. It is as if one should state that there are more cases of cancer in a year in London than in Dover, ignoring the enormous discrepancy in population. It is necessary therefore to state in some way the number of animals from which these cancer cases are drawn, and two methods of enumeration have been adopted. The first, and less reliable, consists in assuming that throughout the period of observation the other causes of death have been operating uniformly at each of the successive periods of life. We can then state the total mortality at each age-period and find what proportion the cancer deaths bear to the total mortality of animals of the same age. The second and more accurate method requires that the cancer deaths (or cases) be reckoned on the number of animals living, of equal age. This is the method adopted in human mortality statistics, the proportional numbers for each year being known as annual death- rates. An attempt will be made in the present paper to adopt this method, with modifications made necessary by the small numbers avail¬ able, to the deaths of mice from cancer.