266 PHYSIOLOGIC GENETICS 



viruses to elicit a variety of leukemias in their hosts suggests the possibility of a single 

 virus producing a variety of tumors within a species. The logical conclusion to this 

 discussion is that the methodology of genetics has contributed, and will continue to 

 contribute, much to the solution of the cancer problem. 



Dr. Nalbandov: A year ago in Russia I learned of a method which impressed 

 me and which may interest you. It involves applying uniform standard stresses (such 

 as electric shock) to inbred strains of mice (C57 and A) and classifying the individuals 

 according to their responses: nervous (unstable nervous system) to nonnervous (stable 

 system). According to V. K. Fedorov (Pavlov Physiol. Inst. Koltushi, Leningrad) 

 mice with an unstable nervous system died very rapidly after inoculation with cancers, 

 whereas mice with a stable nervous system died after a more prolonged period of time 

 and showed many metastases. Mice made neurotic by repeated electrical shocking 

 were more susceptible to cancer (both spontaneous and inoculated) than were their 

 non-neurotic counterparts. In dairy cows responses to light, sound, and electrical shock 

 stimuli were measured and cows classified into four groups from very stable to unstable. 

 The milk yields in 300 days were 6,193 kg. for the most stable group I; 5,516 kg. for 

 group II; 4,918 kg. for group III; and 4,708 kg. for the least stable group IV. 730 



Dr. Pilgrim: I do not know what methods they were using, but most people who 

 work with mice probably consider the C3H one of the calmest and easiest strains to 

 work with and one with the highest incidence of cancer. 



Dr. Nalbandov: That is not the point. They subject them to a uniform stress 

 in order to determine the degree of stability of the nervous system. 



Dr. Heston: Were the growth curves of the mice followed? Cancer is a disease 

 of the healthy, and almost anything one does to make the mouse less healthy, if such a 

 term is permissible, and which will reduce growth rate will decrease the occurrence of 

 tumors. 570 For example, a deficient diet will decrease the occurrence of tumors and 

 a growth-promoting diet will increase their occurrence. 24, 572, 759, 1311, 1312 Various 

 genes affect susceptibility to pulmonary tumors. The gene which increases growth 

 rate of skeleton and muscle is associated with an increase in these tumors, whereas those 

 that decrease growth rate are associated with a decrease in pulmonary tumors. 556, 566 



Dr. Klein: Dr. Heston, you said that in serial backcrossing the agent was elimi- 

 nated due to the reactivity of the females by antibodies. What is the evidence for this ? 



Dr. Heston: No one, to my knowledge, has shown that the mouse can produce 

 antibodies against the mammary-tumor agent. When Dr. Andervont 26 gave the 

 agent to low tumor strain C57BL females these females did not get tumors, but they 

 did not eliminate the agent they received, for they were able to transmit it to foster 

 nursed, susceptible young that later developed tumors. Their own C57BL young, 

 however, could not transmit any agent. In our own segregation studies, 571 among the 

 females resulting from backcrossing F x females to C57BL males one would have expected 

 that some would not have genes for susceptibility to the agent; yet, although many of 

 these backcross females did not get tumors, none of them eliminated the agent com- 

 pletely, for all of them transmitted it to susceptible test females that later developed 



