Origin of S o m e Inbred Mice

The introduction of the use of inbred micc into cancer and other biological research has been a long and slow process. Even at the present time the application of this technic is not by any means universal. A glance at Hartwell 's recent extensive survey of compounds which have been tested for carcinogenic activity (13) will show that, a l t hough the use of inbred mice is largely appreciated, considerable work is still being done on mice of unknown or uncertain origin. For example, in this monograph there are approximately 3,747 references to thc usc of animals in cancer research. Sixteen groups of animals are mentioned. There are 2,202 references to the use of mice (58.7 per cent of grand total); 876 to rats; 339 to rabbits; i t 6 to guinea pigs; 95 to fowls; 34 to dogs; .32 to monkeys; and 53 references to the use of the other 9 minor groups of experimental animals. The 2,202 refercnccs to the use of mice can be scparated into 4 classes as follows: (a) 883 to mice whose origin is not stated; (b) 532 (24.I per cent of the total use of mice) to the inbred strains developed by the present author, the origin ot which will be discussed in this paper; (c) 414 to the use of "heterozygous" t mice (many of the "he te rozygous" mice used were obviously produced by hybridization from our inbred mice, but are not includcd, however, in the computed 24.I per cent; and (d) 373 references to mice f rom all other sources. That is, when the source of mice is definitely, stated (17,319 times) the use of the inbred strains ot~ S t rong was 40.3 per cent of the total use of mice (exclusive o f derived heterozygous animals). This percentage would probably be even greater since many of the references to stocks are too vague for propcr classification; e.g., (a) black agouti, (b) inbred, (c) cancer-resistant, (d) cancersusceptible, and (e) inbred albino. It is the conviction of many geneticists that the use of the inbred mouse in cancer research has made possible many contributions of a fundanaental nature that would not have been made otherwise. Perhaps it would not be out of place to make the suggestion that wi th in the near future all research on mice should be carried out on inbred animals or on hybrid mice of known (genetically cont ro l led) origin where the degree of biological variability has been carefully controlled. A major step in this direction has been taken by investigators at the