THE STUDY OF CANCER 19 



contemplated as a whole, fluctuations in the rate and amount 

 of growth are observed, even when many batches of the in- 

 oculations yield 90 to 100 per cent, of tumours. These fluctuations 

 can be considered from two standpoints : either they are due to 

 variations in the suitability of the mice inoculated, or to others 

 inherent in the tumour cells. While variations in the suitability 

 of the mice, or even of the same mouse at different times, no 

 doubt contribute to their production, they are insufficient to 

 explain all the phenomena. The fluctuations may be revealed by 

 (1) variations in the success of transplantation, (2) a contrast 

 between the sizes of the tumours in different batches, or even 

 in the same batch, (3) a tumour which is growing rapidly may 

 come to a standstill, diminish in size, subsequently grow 

 rapidly, and again diminish, (4) diminution in size, however, is 

 frequently followed by entire disappearance and absorption of 

 the tumour. Those features of growth can be studied in parallel 

 experiments in such a way as to bring out the probability that 

 they are for the most part manifestations of a variation in 

 the assimilative energy of the tumour cells themselves. In 

 the human subject there are corresponding fluctuations in the 

 growth of cancer. In one part of a tumour growth is proceeding 

 rapidly, in another part slowly. Periods of exacerbation alter- 

 nate with periods of amelioration. Further, secondary nodules 

 of growth are known to disappear while others are growing, 

 and occasionally primary growths have disappeared. The 

 observations made on mice emphasise the importance of those 

 clinical features, largely discredited, in the human subject, since 

 they have been often interpreted to mean that the growths 

 exhibiting them were not cancer. The experimental propa- 

 gation of cancer has demonstrated conclusively that mice can 

 recover from artificial tumours. In the elucidation of this 

 process, and of its counterpart in spontaneous cancer, lies the 

 hope of assisting the surgeon. At present I can only foresee a 

 still remote possibility that dissemination from the primary 

 focus may be hindered; I can foresee no probability that the 

 primary focus will be got rid of by other means than early 

 surgical removal. 



The ultimate absorption of transplanted tumours requires to 

 be considered in relation to certain other facts. The mice in 

 which it has taken place are protected highly against subsequent 

 inoculation with the same growth, and to a lesser extent against 



