SUSCEPTIBILITY TO TRANSPLANTABLE TUMORS 133 



6. Removal of the gonads does not change the massed per- 

 centage reactions for individuals of a non-susceptible race. This 

 bears out the previous conclusion that the number of percentage 

 reactions in a given strain depends upon the genetic constitution 

 of the individuals. 



7. Gonadectomy produces, in the stock employed, a significant 

 increase in percentage reactions in mice attaining sexual maturity 

 (age class 3). 



8. Gonadectomy causes an approach towards a 'neutral' 

 type (loss of characteristic differences between sexes) in the 

 percentage of reactions towards both tumors used, just as it 

 does in the case of morphological characteristics (Hatai and 

 others) . 



9. By the removal of the gonads, the individuality of tissues 

 and the normal functioning of the age factor can be interfered 

 with. 



10. A severe shock caused by such an operation as gonadec- 

 tomy produces, in some cases at least, a resistant state to trans- 

 plantable tumors that is at its maximum from five to ten days 

 after the operation. 



Without the assistance of several institutions and individ- 

 uals, the present experiment w^ould have been impossible. 



I am indebted to the Department of Zoology, Columbia Uni- 

 versity, for a grant of the John D. Jones Scholarship Fund during 

 the summer of 1920. The Carnegie Institution of Washington, 

 through the Department of Genetics, has very kindly assisted 

 the experiments from a financial standpoint during the winter 

 of 1920-1921. To Dr. C. C. Little I am deeply indebted for 

 numerous favors, especially for the suggestion of the problem, 

 his kind supervision throughout the experiment, and his pains- 

 taking criticism and help in the preparation of the manuscript. 

 Drs. G. N. Calkins, F. C. Wood, and T. H. Morgan have offered 

 valuable suggestions. Through the kindness of Drs. James Ewing 

 and H. J. Bagg, the technical preparation of the material for 

 histological examination and the making of the microphotograph 

 were done at the Memorial Hospital, New York City. To the 



