108 IMMUNOLOGY 



in resistance of various inbred litters of rats to S. enteritidvi in- 

 fection. Schott (1932) has also studied the effect of selection on 

 the resistance of mice to S. aertrycke and Monreas (1932) of rab- 

 bits to Br. abortus, var. suis. These have all shown that under 

 experimental conditions, inheritance is important both in resistance 

 and susceptibility of mice and rabbits to infection. Similar con- 

 clusions have been drawn by Lewis* (1928) from an extensive 

 study of experimental tuberculosis in guinea pigs. He says that 

 his "observations agree very well with the older conception of 

 an inlierited predisposing constitutional diathesis as a significant 

 factor in the incidence of tuberculosis. ' ' 



These views are somewhat at variance with those of Topley, 

 Wilson, Lewis and Greenwood (Topley, and Wilson, 1929, 1936) 

 who conclude from a study of statistical data on host survival 

 during epidemics that active immunity due to either recognized or 

 subclinical infection is a more important factor in survival than 

 selection of innately resistant animals. Similar conclusions have 

 been drawn from Armstrong's studies on mice surviving nasal in- 

 stillation of the St. Louis encephalitis virus. He found them rel- 

 atively resistant to a second instillation and concluded they had 

 become immunized. 



Webster and Hodcs (1940) point out certain sources of error 

 in the experiments cited above and present very convincing ex- 

 perimental evidence in support of their previous conclusions that 

 inheritance factors play an important role in survival. Their re- 

 sults cast grave doubts upon the conclusions of Topley et al. as well 

 as those of Armstrong. They found that survivors were almost 

 exclusively individuals known to be innately resistant and that 

 there was no tendency for known susceptibles to become immunized 

 through exposure before or during epidemic times. They grant the 

 possibility that future research may show that survivors of an 

 epidemic may develop through infections, what Webster and Hodes 

 call a luxury iynmunity. They^were unable to immunize susceptibles 

 by giving them sublethal doses of mouse typhoid bacilli or St. 

 Louis encephalitis virus by a natural route. 



These observations may not invalidate the contention of Topley 

 and Wilson that under field conditions the possession of an active 



♦Lewis, Paul A., Loomis, D. : J. Exper. Med. 47: 1437. 1928. 



