SUSCEPTIBILITY TO TRANSPLANTABLE TUMORS 93 



ually, decreases to a minimum. During maturity, the gonads 

 are relatively constant in their activity; at this time suscepti- 

 bility is also relatively constant. With the decreased physio- 

 logical activity of the gonads and accompanying the onset of 

 senescence, susceptibility toward transplantable tissue increases 

 in the reverse order — slowly at first and then rapidly. 



One more experiment dealing with the age groups of the mice 

 for the dBrB tumor may be given here. Eliminating the recog- 

 nized significant differences between class 1 and the three middle 

 classes on one hand and between the three middle classes and 

 class 5 on the other, we have attempted to analyze further the 

 so-called rhythmic activitj^ of the tumor cell. In the following 

 chart only individuals belonging to the three middle classes were 

 employed. There is no significant difference in the susceptibihty 

 of these animals, so the objection cannot be raised that any 

 rhythmic reaction encountered may be due to individuals from 

 different age groups being used from time to time. Figure 8 

 represents the three time groups, calculated from the same data 

 given on page 86 with the one correction of eliminating the very 

 young and very old mice. 



Tabulation 

 Time period (1) 167 negative : 15 reactions ±2.49 or 8.24% ± 1.36 

 Time period (2) 274 negative : 20 reactions ±2.90 or 6.80% ± 0.99 

 Time period (3) 273 negative : 19 reactions ±2.83 or 6.51% ± 0.96 

 Difference between: 



Time period (1) and (3) 1.73% ± 1.66 or 1.04 times probable error 

 Time period (2) and (3) 0.29% ± 1.38 or 0.21 times probable error 

 Time period (1) and (2) 1.44% ± 1.68 or 0.86 times probable error 



This experiment furnishes still clearer results than those given 

 on page 86. We are therefore justified in our previous conclusion 

 that the dBrB tumor has retained a constant reaction potentiality 

 throughout the experiment. 



/. Age at inoculation (dBrA). As with the dBrB tumor, the 

 three middle-age groups (classes 2, 3, and 4) are classified to- 

 gether to simplify the calculations. Comparing the middle-age 

 group with class 1 individuals, we obtain the following graph 

 (fig. 9, p. 95.) 



