THE St UDY.OFr- 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 goto 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 
thetumour. 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 
