IT is often assumed that the serum of a healthy uninoculated rabbit contains only insignificant amounts of antibacterial agglutinins. This view is largely supported by the findings of Gibson (1930), but Boyd (1939-40) and Messer (1943) have drawn attention to the occurrence of agglutinins in considerable concentration in some " normal " rabbit sera. Indeed, with a agglutinin, the natural antibody titres may be as high as those found in sera from immunised animals (Stamp and Stone, 1943-44 ; Francis and Buckland, 1945).I n the present work, certain paracolon bacilli isolated from desoxycholate-citrate-agar plate cultures during the examination of fieces from cases of enteritis or their contacts were found to have biochemical reactions superficially resembling those of certain specific pathogens and to be agglutinated to titre by a considerable number of batches of Oxford standard agglutinating sera prepared against different organisms. I n preliminary absorption experiments with antisera to Shigella sonnei and Shigella jlexneri, types Newcastle and Boyd 103, the paracolon bacilli failed to remove the specific agglutinins for the dysentery bacilli, and the homologous dysentery bacilli had no effect on the ability of the sera to agglutinate the paracolon strains. Subsequently the paracolon strains were found to be agglutinated to high titres by the sera of two healthy uninoculated rabbits. These rabbit sera also agglutinated lactose-fermenting and non-lactosefermenting coliforms from human fieces or contaminated war wounds. The agglutinins in these sera were studied in absorption experiments and the results form the subject of this paper.
MethodsStrains. Four strains of paracolon bacilli (PR, PW and PM from faxes, P 6 from a contaminated war wound) and 4 strains of Bacterium coli of Wilson et al. (1935), type I (CA and CB from fseces, C 5 and C 7 from wounds) were used for the main absorption experiments. Part of the work was repeated with three known tc strains, including the classical 1721, kindly provided by Dr Doris Stone.Bacterial suspensions. The organisms grown on Lemco-agar slopes for 18 hours at 37' C. were washed off in saline (0.85 per cent. sodium chloride)
