1906.] Experimental Analysis of the Growth of Cancer. 197 



old and in young animals. The extent to which the youth of the animals 

 usually favours the continuation of growth after transplantation may he 

 illustrated by the results of 18 series of inoculations, in which portions of the 

 same parent tumours were transplanted simultaneously into young and adult 

 animals respectively ; 214 implantations into adult animals three to six 

 months old yielded 62 tumours, or 29 per cent, were successful; 363 

 implantations into young animals five to seven weeks old gave 172 tumours, 

 or 47 per cent, were successful. This result is by no means an extreme case, 

 either as regards proportion of successes or as regards difference in age of 

 the inoculated animals. 



3. When the precautions above indicated are observed, the individual 

 variations in the general suitability of different mice of the same race and 

 age are negligible if implantation be performed in the same site, provided 

 sufficiently large numbers are used. We have preferred the subcutaneous 

 tissue of the back. The attempt to perform collateral series of intra-peritoneal 

 inoculations was abandoned, owing to the frequency with which growth 

 within the peritoneum had occurred secondarily by extension from tissue 

 implanted in the abdominal muscles. 



4. We have endeavoured to transplant pieces of healthy -looking tissue of 

 uniform size by means of hypodermic needles, and have obtained more 

 satisfactory results by this method than by breaking tumours down into an 

 emulsion and injecting larger quantities of tissue suspended in physiological 

 salt solution. With certain reservations the rate of development and the size 

 the daughter tumours will attain within 10 days is directly proportionate to 

 the amount of healthy tumour tissue implanted ; 0*02 to - 03 gramme of 

 tissue usually gives larger tumours within a given time interval than - 005 to 

 0"01 gramme. 



5. When the conditions referred to in the four preceding paragraphs are 

 maintained uniform, fluctuations independent of them appear, and we shall 

 endeavour to show that they are, in all probability, natural features of 

 proliferation. The detailed study of these fluctuations has been undertaken 

 with the tumour which has proved readily capable of transmission during the 

 longest period yet attained, viz., that of Jensen. This tumour has now been 

 propagated for four and a-half years, without permanent alteration in its 

 histological characters or its behaviour. We have obtained success in from 

 5 to 90 per cent., occasionally even in 100 per cent., of the animals inoculated, 

 the percentages being based on data obtained from those mice which were 

 still alive* 10 days after the inoculations were made. The amount of tissue 



* It is our practice to kill from time to time a number of mice during the first 10 days 

 after inoculation, in order to examine the site of implantation. Tumours of transplant- 



