112 LEONELL C. STRONG 



The most important point to emphasize in this connection is 

 the fact that if individuals are inoculated five to ten days after 

 operation, they give a significantly smaller number of percentage 

 reactions than if inoculated at the other times. There is no 

 significant difference between controls and the first-time group 

 (0 to 5 days). 



By including the data on second-inoculation individuals as 

 well as first inoculations (since there is no significant difference 

 between first- and second-inoculation observations when the 

 data are massed), we are able to study further the apparent 

 deleterious effects of the operation (fig. 28). 



The data for the first three points of the curve are the same 

 as those given on page 110. The data for the additional points 

 are as follows: 



(Group 4) 16 da- 60 da. 106 negative : 4 reactions ±1.33 or 3.64% ± 1.21 

 (Group 5) 60 da.- 90 da. 177 negative : 10 reactions ±2.08 or 5.34% ± 1.12 

 (Group 6) 90 da.-120 da. 250 negative : 17 reactions ±2.68 or 6.36% ± 1.07 

 (Group 7) 120 da.-150 da. 93 negative : 4 reactions ±1.32 or 4.12% ± 1.36 

 (Group 8) 150 da.-180 da. 73 negative : 1 reaction ±0.67 or 1.35% ± 0.91 

 Differences : 



Controls-Group 4 5.57% ± 1.37 or 4.07 times its probable error 

 Controls-Group 5 2.87% ± 1.30 or 2.21 times its probable error 

 Controls-Group 6 2.85% ± 1.26 or 2.26 times its probable error 

 Controls-Group 7 5.09% ± 1.51 or 3.37 times its probable error 

 Controls-Group 8 7.86% ± 1.15 or 6.83 times its probable error 



Three items concerning this curve will be emphasized here: 

 1) Individuals inoculated from five to ten days after operation 

 are significantly more resistant to the tumor tissue, 2) from 

 sixteen days on there is a gradual increase of susceptibility until 

 the maximum is reached with individuals inoculated about 110 

 days after operation, and 3) the result obtained by keeping in- 

 dividuals for about 150 days and longer between operation and 

 inoculation (irrespective of the age at which they were gonadec- 

 tomized) is the same as that obtained by inoculating individuals 

 that had been operated on when they fell in age class 5 (old 

 mice) — there is an approach toward zero susceptibility in each 

 case. It may be well to recall that in normal individuals sus- 

 ceptibility to transplantable tissue increased with old age. 



