SUSCEPTIBILITY TO TRANSPLANTABLE TUMORS 73 



be taken up next under the consideration of 'virulence or 

 adaptation.' 



Tyzzer and Little, on their work with the Japanese waltzing- 

 mouse tumors (J. W. A. and J. W. B.), determined that every 

 mouse of that strain inoculated grew the two tumors progressively 

 and at a constant rate of growth (there was no significant differ- 

 ence between the rates of growth of any two transplanted tumors 

 in those series). Evidently, the results observed by Bashford, 

 Murray and Bowen and Calkins may have been largely due to 

 fluctuations in the genetic constitution of the 'market mice.' 

 WTiere a definitely proved constant homogeneous race of mice 

 is employed, no rhythms of growth activity are encountered 

 throughout a period of over ten years. 



h. Virulence or adaptation. It has long been recognized that 

 by continually inoculating tumor tissue into animals of a foreign 

 strain, one can gradually increase the percentage of takes until 

 the maximum is reached. The English observers were the first 

 to determine that this percentage of positive tumor takes fluc- 

 tuates between the minimum and maximum for any given race. 

 At present two explanations are possible: 1) the tumor cell has 

 an inherent capacity of adapting itself to a foreign host or, 2) 

 the cell possesses fluctuating 'virulence.' 



The first explanation has the support of Bashford, Murray, 

 Haaland, Bowen, Cramer, Woglom, and others; the second that 

 of Ehrlich and Apolant. 



The arguments for and against these explanations are too 

 well known to be repeated here. We may emphasize, however, 

 that neither theory is entirely acceptable. Each assumption 

 rests on the old idea of the inheritance of acquired character- 

 istics, although several attempts have been made to mask this 

 implication. 



The conception of virulence has been analyzed into two ele- 

 ments by Apolant, 1) transplantability, determined by the per- 

 centage indication of positive takes, and, 2) prohferative energy, 

 calculated from the rate of growth of the transplanted mass. 

 In the light of modern genetical investigation, both of these 

 terms lose much of their significance. The percentage indica- 



