300 



BIOLOGY OF THE LABORATORY MOUSE 



Complete or partial castration and ovariectomy have also been studied 

 in relation to growth of transplanted tumors. The results obtained by dif- 

 ferent investigators have varied as have the conclusions drawn from them. 

 This is probably due to the fact that various stocks, ages and tumors 

 have been used. An additional variable has been provided in the interval 

 between operation and implantation of the tumor. 



One of the most complete and careful studies of this question has been 

 made by Strong (72). He concludes: 



I. Removal of the gonads does not change the massed percentage reac- 

 tions 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. 



Table 11 



2. Gonadectomy produced, in the stock employed, a significant increase 

 in percentage reactions in mice attaining sexual maturity. 



3. Gonadectomy causes an approach towards a "neutral" type (loss of 

 characteristic differences between sexes) in the percentage of reactions — just 

 as it does in the case of morphological characteristics. 



4. By the removal of the gonads, the individuality of tissues and the 

 normal functioning of the age factor can be interfered with. 



5. A severe shock caused by such an operation as gonadectomy produces, 

 in some cases at least, a resistant state to transplantable tumors, that is at 

 its maximum from five to ten days after the operation. 



Other investigators have found similar shock effects following operative 

 removal of the spleen. 



In all of these physiological studies a common criticism can be made. 

 It is roughly the same as that applied to investigations of diet ; namely, that 

 too little work has been reported on material in which the number of vari- 

 ables has been reduced to a minimum. 



