SUSCEPTIBILITY TO TRANSPLANTABLE TUMORS 87 



There is no significant difference between any of the three 

 periods. It will be noted, however, that there is a gradual 

 decline in the percentage of reactions from the first period 

 through the third. This decline is not significant for the entire 

 period of the experiment which consumed about a year. Whether 

 this decline will continue in the future is problematical and 

 will be referred to later. It may be well, however, to emphasize 

 the fact that this decline is primarily caused by the use of 

 numbers of individuals from the different age groups, more 

 very young individuals being employed at the beginning of 

 the experiment than at any other time. All we can conclude 

 from the results is that the adenocarcinoma dBrB has probably 

 retained a constant reaction potentiality throughout the present 

 experiment. 



c. Exceptional dBrA. The same phenomenon was encoun- 

 tered with the dBrA tumor, with one exception. Experi- 

 ment N (started August 16, 1920) gave such a large num- 

 ber of positive reactions that the question arose whether we 

 were dealing with the same tumor reaction that we had ob- 

 served up to that time. In fact, this one experiment gave more 

 indications of growth than did all the other experiments in- 

 volving the dBrA tumor combined. This experiment also 

 included the only wild mouse, adult male W238, that ever grew 

 the dBrA tumor progressively. Comparing the percentage 

 of reactions of the exceptional dBrA tumor (xA) with all the 

 other dBrA (nA), we obtain the graph on page 85 (fig. 3). 



With the exception of the last point, it will be seen that every 

 point in the exceptional dBrA reaction curve is significantly 

 greater than the corresponding point in the normal dBrA curve. 

 The data relative to this matter may be combined as follows: 



1. Exceptional dBrA 55 negative : 23 reactions ±2.72 or 29.48% ± 3.49 



2. Normal dBrA 705 negative : 15 reactions ±2.58 or 2.08% ± 0.36 



Difference 27.40% ± 3.51 



The difference is thus 7.81 times its probable error 



The difference between the two dBrA tumors is therefore 

 mathematically significant. 



