No. 636] GUINEA PIGS AND TUBERCULOSIS 43 



and zero-bloods in lots 10-14 and in a combination of 

 lots 3, 4, 5 with lots 7, 8, 9. 



Curiously enough the crossbreds with no blood of 

 family 35 do not show the improvement over their an- 

 cestral inbred families shown by the half and quarter 

 bloods. They exceed the average of families 2, 13 and 

 32 by only 13 per cent, in lots 3-5, 8 per cent, in lots 7 9 

 and 7 per cent, in lots 10-14. They are not consistently 

 superior to the best of these families, family 2. There 

 seems to be dominance of resistance on the whole but no 

 supplying of complementary factors for resistance such 

 as was indicated in the crosses of family 35. This indi- 

 cates that families 2, 13 and 32 are in the main sus- 

 ceptible because of the same genetic factors. The rela- 

 tions of the factors present in the different families is a 

 question on which it is hoped more extensive evidence 

 can be presented later (Charts 6 and 7). 



Inhekitance of Eesistance and Sex 

 The crosses involving family 35 give some evidence on 

 the inheritance of resistance from sire and dam. The 

 average length of life in reciprocal crosses is given in 

 Table XV. 



TABLE XV 



The Average Length of Life of Males and Females from KECiPKOCAii 

 Crosses Involving Family 35 



d" (35) X ? (misc.) 7^ 63.6 



5? 59.4 



12 6L9 



(35 X misc.) X ? (misc.) 6 64.0 



d- (misc.) X ? (35 ; 



The results are irregular, as might be expected with 

 such small numbers, but they show that there is trans- 



