SUSCEPTIBILITY TO TRANSPLANTABLE TUMORS 123 



4- Sex 



The disputed factor of sex as underlying susceptibility to 

 transplantable tissue has already been briefly discussed (p. 98). 

 Some recent investigations relative to the sex factor have not 

 entirely verified the previous conclusions of Loeb, Ehrlich, and 

 the members of the Crocker Laboratory. The above-mentioned 

 investigators have not observed any differential effect of sex 

 upon susceptibility to transplantable tumor tissue. In the 

 following paragraphs an attempt will be made to reconcile the 

 two opposing theories by pointing out that the sex and age fac- 

 tors as underlying susceptibility to transplantable tumors may be 

 explained as the result of a common group of causative agents 

 affecting the physiological state of the tissues. 



The first work of importance that disagreed with the findings 

 of the various investigators already mentioned was done by 

 Little. This work is a continuation of his and Tyzzer's previous 

 investigations with the Japanese waltzing mouse sarcoma J. W. B. 

 Little predicted that the first back-cross generation individuals 

 (produced by crossing the susceptible Fi hybrids between the 

 Japanese waltzing mice and the non-susceptible common stock 

 back to the non-susceptible parent strain) would behave similarly 

 to the second fiUal generation of hybrids. This he later demon- 

 strated, although, as expected, fewer individuals of the back- 

 cross generation than of the Fo generation were susceptible to 

 the continued growth of the tumor cell. The percentage of 

 positive growths expected can be determined beforehand by 

 mathematical calculation from mendelian principles, and is 

 therefore the most accurate work that has been done with trans- 

 plantable tumor tissue. 



In this partially susceptible strain (B.C) Little determined 

 that the percentage of growth increased with age (4.6 X P. E.) 

 (when very young mice were employed). This difference is 

 mainly confined to the female sex. WTien a definitely proved 

 non-susceptible race was used, susceptibility toward transplanted 

 tissue decreased with age up to the attainment of sexual maturity. 

 Here again this difference was confined mostly to the female sex. 



