THE STUDY OF CANCER 13 



the two forms of growth are interchangeable experimentally. 

 For different carcinomata Murray, Cramer, and myself have 

 shown that this interchange of the mode of growth is dependent 

 on the anatomical surroundings of the tumour, and not on an 

 alteration of the properties inherent in the tumour cells. It 

 therefore suffices to study mere growth, and in doing so one 

 may disregard the features of most use in the current classifica- 

 tion of tumours. 



The transplantation of a sporadic tumour is effected according 

 to our method as follows : The tumour is removed from the 

 animal so as to avoid bacterial contamination, and weighed. 

 It is divided into portions which are placed in separate 

 receptacles. The portions are then inoculated by means of 

 hypodermic needles, minute fragments {circa o'oi — C03 grm.) 

 being broken off and inserted subcutaneously. The tumour is 

 thus distributed over as large a number of mice as possible — 

 it ' may be fifty or four hundred. The experimenter must then 

 possess his soul in patience. Rarely is he rewarded by the 

 appearance of true tumours, at the site of inoculation, within 

 a fortnight. He may have to wait from three to six months 

 before the inoculations can be pronounced to have fallen out 

 either positively or negatively. 



The nature of the result is determined mainly by two factors : 

 variations in the suitability of the soil the mice afford for the 

 growth of the grafts introduced as above ; and variations in the 

 character of the tumour cells, not only of different tumours, but 

 of one and the same tumour. The suitability of the soil may be 

 taken to be fairly constant when large numbers of young mice 

 of the same age (six to eight weeks) and of the same stock are 

 employed. Adult and old mice are not only much less suitable 

 than young animals, but they also exhibit greater individual 

 idiosyncrasies. Normal mice may be said to offer a certain 

 unsuitability, or to be resistant, to inoculation, when tumour 

 cells are transferred to them after removal from their natural 

 environment in the animal in which they developed. This 

 resistance acts as a sieve, sifting out the tumour cells which are 

 unable to nourish themselves and proliferate in this new and, 

 it may be, very strange environment. Thus the positive results 

 of the primary transplantation seldom form a high proportion of 

 the animals inoculated. They are probably obtained by the 

 segregation of groups of cells of high assimilative energy and 



