DEPARTMENT OF GENETICS. 123 



In crosses between albinos and dilute browns, however, the differ- 

 ence should not be nearly so great, and the number of factors should 

 therefore be distinctly smaller. 



The behavior of the F2 hybrid generation which has been raised and 

 observed by Dr. L. C. Strong is in complete accord with this expecta- 

 tion. The B tumor gives a total of 108+ to 89 — . If a two-factor 

 difference is involved, a 9 : 7 ratio is expected. This, in the number of 

 mice involved, would mean 110.7+ to 86.3 — . The dbrA tumor is 

 the same which, by extensive tests with non-susceptible wild house- 

 mice. Dr. Strong found showed significantly fewer indications of growth 

 than did tumor dbrB. The genetic behavior of this tumor gives an 

 interesting clue to the nature and extent of its divergence from tumor 

 B. 88 animals of F2 are plus to tumor A and 110 are minus. On a 

 three-factor basis of 27:37, the numbers expected are 83.5+ to 

 115.5-. 



The back-cross of Fi by albino produced corroboratory evidence in 

 each case. Thus, in this generation, tumor B gives 10+ and 44 — , 

 the expectation on a two-factor basis being in this case 13.5+ to 40.5 — . 

 Tumor A gives a total of 8+ to 46 — , the expectation being 6.75 to 

 47.25. The conclusion can, therefore, be drawn that in the inheritance 

 of susceptibility and non-susceptibility to the B tumor, a ^u'o-factor 

 difference between the dilute brown and albino race is involved, while 

 for the A tumor three factors are concerned. This drives the work 

 with inoculable tumors a point nearer to the isolation of animals and 

 strains differing in a single Mendelian factor. 



Miss Helen Bloomer and Miss Marie Poland have assisted in the 

 genetic work during the summer. More than 200 hybrids other than 

 those recorded have been inoculated and are awaiting observation, 

 while a total of more than 1,200 hybrids are now available for breeding. 



Dr. Strong, who has practically completed the work on inoculation 

 of wild mice with tumors dbrA and dbrB, reports as follows : 



"Several points of genetic interest appear to be brought out by this experi- 

 ment. Among these is the fact of which preliminaiy mention was made 

 last year that physiological tests are more delicate than histological ones 

 in that they record slight differences in the tissue of two tumors, which were 

 histologically indistinguishable . 



"The experiment is a continuation of the one mentioned in the previous 

 report. At present the data relative to tliis point are as follows : 



Total dbrB 876. Negative:80=fc5.68 reactions or 9.23 per cent ±0.66. reactions 

 Total dbrA 705. Negative: 15='=2. 55 reactions or 2.08 per cent =1=0.35. reactions 



Difference 7.15 per cent ±0.74 



The difference is thus 9.66 times its probable error. 



"The susceptibility curve during the full age-cycle for gonadectomized 

 individuals is quite distinct from that of the unoperated controls. 



"Susceptibility is influenced by several general factors, among which age 

 is one of the most important. The present experunent confirms a similar 

 one carried out by Dr. Little with sarcoma J. W. B. It, however, goes further 



