1. Four mouse lines have been tested for “H” and “O” antibody production following inoculation with Salmonella typhi murium and S. enteritidis; two of these lines had been selected for resistance and susceptibility but not inbred; two, D and E, had been brother-sister inbred for over thirty generations but not selectively as far as resistance is concerned.
2. After immunization with S. typhi murium:
(a) Female mice, in all four lines, tend to give higher “H” and “O” titres than do males, a positive correlation between ability to produce antibody and resistance to infection being thus established.
(b) Interline differences exist for both these antibodies. Those concerned with “H” antibody may be correlated with resistance. In the case of “O” antibody, no correlation is suggested.
3. After immunization with S. enteritidis:
There appears to be no correlation sexually or interlineally between resistance and antibody production. That genetic differences exist, in respect of this organism also, is shown by the fact that the pure lines, D and E, give a better antibody response than the selected lines A and B. When tested for immunizability by subsequent infection with S. enteritidis no useful information could be obtained with strain A or B owing to their great internal variation. Strains D and E both showed a gain in expectation of life following immunization. The more resistant strain D showed a significantly greater gain than did E, the strain with a lower natural resistance.
4. The titres of normal “O” enteritidis-antibody found in the four lines indicates that there may be a negative correlation between the titre of these antibodies and resistance to infection with S. enteritidis.
5. The significance of the above findings is discussed and it is stressed that a significant correlation between resistance and antibody formation does not imply that the two phenomena are causally related.
6. It is pointed out that strains that have been inbred even without selection react far more homogeneously in the infection experiments here described than do strains that have been selected but not intensively inbred.