Differences in Bactericidal Power of the Blood Within an Inbred Strain of Rats

Abstract

During the course of experiments on the role of heredity in the resistance of rats to infection with S. enteritidis, some discrepancies from the uniform mortality rate to be expected in a highly inbred strain of animals were encountered. 1 An immunological study of the animals from this strain showed marked differences in the bactericidal power of the whole blood. Loeb and King 2 had previously found marked differences in reaction to tissue transplants in rats within each of the Wistar “A” and “B” strains.

The animals used in our experiments were descended from one pair of rats of the Wistar “A” strain, obtained in 1924 from Doctor Helen Dean King. These rats were then in the 48th generation of brother-sister matings. These brother-sister matings have been continued in our tests. All rats used have been shown not to excrete S. enteritidis in their feces and were carefully kept free from exposure to this infection. Blood taken from the heart of each animal was mixed with just sufficient sodium citrate to prevent clotting, and drawn into capillary pipettes previously coated with a thin layer of a saline dilution of an 18 hour culture of S. enteritidis, the method being that proposed by Heist and Solis-Cohen 3 for determining the pneumococcidal power of blood. After the open end of the pipettes had been sealed in the flame, they were placed in the 38° incubator for 4 hours. The contents of each pipette were then expelled into a Petri dish of fluid agar and incubated over night, then the number of colonies counted. Suitable control tubes were inoculated to demonstrate the viability of the organisms and to indicate the numbers of organisms present in each dilution.