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.

    5/14 page 69
    The first method, that of estimating the cancer fraction of the total mortality, was adopted in the earlier accounts of these observations(1’2) and also by Tyzzer.3 As the breeding of fresh mice suffered no inter¬ ruption, a date was fixed up to which the enumeration was to be carried. All the animals which had died from causes other than cancer were counted, and those whose ages at death differed by less than three months were added together, commencing with animals which were at least six months old at death. A difficulty arose in deciding the age- periods to which the cancer cases should be ascribed. Ordinarily cases of spontaneous cancer in the mouse terminate fatally within four to six weeks after the discovery of the tumour if left to themselves. If the tumours be extirpated death may be postponed for several months. On the other hand, the animal may die under the anaesthetic or be sacrificed early for other reasons. Hence the age at death of cancer mice bore a highly variable relation to the age of onset of the disease, and it was decided to adopt the age of onset as determining the age-period to which the animals should be ascribed, rather than the age at death. As some of the cancer cases were discovered just before the day selected for the enumeration, the mice living at the time were also counted and added to the totals of dead mice in the age-periods embracing their ages on the * census ’ day. TABLE II A ge-p erio d in M onths 6-10 -13 -16 -19 -22 -25 over 25 Totals. No tumour Dead 165 126 75 74 59 56 43 598 Living • ?5 16 12 17 5 1 0 66 Tumour mice • 13 24 36 34 12 12 5 136 Total 193 166 123 125 76 69 48 800 Percentage . • 6-7 I4-S 29-^ 27-2 15-8 17-4 io*4 16-6 (The first age-period is of 4 months’ duration, 6-10 months. This gives a more uniform distribution at the higher age-periods than is obtained with the periods 6-9-12, &c.) With all this additional information added, the first table takes the form seen in Table II. The discrepancy between the first age-period and the middle ones is now greater, and in particular the two highest age-periods are found to contain so few animals that their small number of cancer cases constitute a higher proportion of the total deaths at these ages than do the more numerous cancer cases at the first age-period. Another way of stating the results of this table is to say that one out of every six animals reaching the age of six months ultimately dies of cancer, while of mice dying after reaching the age of sixteen months, one in every five falls a victim. The successive estimations of this kind which have already been made during the past four years have given similar results, and there is so far a justification of the fundamental assumption of a fair uniformity, in the operation of the other causes of death. The segregation of the
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