68 LEONELL C. STRONG 



%. Sex (dBrB) 98 



k. Sex (dBrA) 99 



I. Sex composite dBrB and dBrA 100 



m. Gonadectomy 102 



n. Age susceptibility in normal and gonadectomized mice 109 



0. Influence of operation 110 



p. 'Adaptation' 116 



III. General discussion 117 



1. Value of proved stocks 117 



2. Fluctuations in growth energy or adaptation 119 



3. Age 121 



4. Sex 123 



5. Gonadectomy 127 



IV. Conclusions 132 



I. INTRODUCTION 



1. Contributions to the genetics of cancer 



The first part of the following section reviews those genetic 

 investigations that contribute to an explanation of the conclusions 

 reached in this paper. Most of the work, unfortunately, has 

 been published in periodicals not generally seen by medical 

 investigators. Some of the w^ork has been of such a nature that 

 it has led only to skepticism. 



Three contributions to the genetics of cancer appear to be 

 worthy of special significance. These relate to experiments on 

 transplantable tumors, and involve — 



a. The recognition of the factor of race. 



b. The demonstration of mendelian segregation and recom- 

 bination of factors that underlie susceptibility to transplantable 

 tumors. 



c. The possibility that the causation of spontaneous neoplasms 

 may be due to a process of mutation. 



a. Race. Up to within the last few years, most investigators 

 in this field considered the phenomenon of race as a factor under- 

 lying susceptibility to transplantable tumors to be of secondary 

 importance. It has become evident, however, that market mice 

 are not reliable for experimental work in cancer. Where the 

 same tumor tissue is inoculated into mice that have been proved 

 to be homogeneous in their genetic constitution, no rhythms of 



