1912.] Resistance to the Growth of Implanted Cancer. 



203 



Murray, and Haaland,* since they have shown that the resistance to 

 re-inoculation which a tumour-bearing animal frequently exhibits, is of the 

 nature of an active immunity. This development of an active resistance 

 during the growth of a transplanted tumour is a most important factor in 

 determining the character of growth which a tumour will show, and the 

 following experiments will demonstrate that this power of rendering a soil 

 unsuitable for further inoculations is a distinctive feature of various tumour 

 strains. 



The procedure adopted has been to inoculate in one flank a series of young 

 animals with a given tumour strain, and then to excise all the growths after 

 10-30 days, i.e. after intervals long enough to allow the tumours to attain a 

 considerable size, 1-4 grm. One, two, or three days after extirpation, the 

 animals have been inoculated on the other flank with a tumour of the same 

 or of another strain. In this way two readings are obtained ; the result of 

 inoculating a given series of normal animals, and the result of inoculating 

 the same animals after a tumour had been growing in them over a known 

 period. The precise way in which the experiments have been carried out 

 will be rendered clearer by the accompanying charts, which portray the 

 tumours first inoculated as black silhouettes, whilst the tumours inoculated 

 after operation, as also the controls to the second inoculation, are outlined in 

 black, and filled in with dots. 



The experiment with strain T, shown in fig. 3, exemplifies the course of 

 such an experiment conducted with a progressively growing tumour strain. 

 Eleven mice bearing this tumour had their growths excised on the 33rd day, 

 and were re-inoculated with carcinoma 63 two days later. The 11 animals 

 all remained free from recurrence, and in every case strain 63 gave rise to a 

 rapidly and progressively growing tumour. When strain 63 is subjected to 

 a similar analysis, it has been found to give a result similar in every respect 

 to that just shown with strain T. These two carcinomata do not affect the 

 suitability of mice for subsequent grafting, and have been much employed in 

 the present series of experiments, where it was desired to obtain a very 

 accurate estimate of the suitability of a series of mice for transplantation. 



The discussion will now be directed to a tumour exhibiting the other 

 extreme type of growth, namely, one which gives rise to temporary growths 

 only. The number of transplantable tumours exhibiting this peculiarity is 

 large, but the date at which spontaneous absorption sets in varies widely 

 from series to series, and from animal to animal, so that the majority of 



* Bashford, E. F., Murray, J. A., and Haaland, M., " Eesistance and Susceptibility to 

 Inoculated Cancer," 'Third Scientific Report of the Imperial Cancer Research Fund, 

 1908, p. 359. 



P 2 



