Transient Fluctuations in the Resistance of Mice to Infection withB. aertrycke

Abstract

1. The virulence of a given strain ofB. aertryckewas tested on 54 occasions during the 3-year period, October 1926–October 1929. Each test was made by inoculating intra-peritoneally about 100 viable organisms into 20 parti-coloured mice, usually of 17–23 grm. in weight, drawn at random from the general laboratory stock. The average number of specific deaths caused by this procedure was 12·71 ± 3·39, but very marked deviations were noticeable, varying from a minimum of 5 to a maximum of 20. These deviations occurred without any observable regularity, and appeared to have no definite seasonal relationship. Evidence is brought to suggest that they were chiefly determined not by variations in the dosage or in the virulence of the strain, but by fluctuations in the resistance of the mice.2. The meaning of the term “resistance” is discussed, and it is suggested that the term “fluctuating immunity” should be used to denote those variations in resistance which occur from time to time, and which are due to alterations in the physiological behaviour of the animal dependent on changing environmental conditions. This fluctuating immunity should be distinguished from innate, inherited, orgenetic immunity on the one hand and from acquired immunity on the other.3. It is pointed out that the existence of fluctuations from time to time in the susceptibility of animals to infection renders fruitless any attempt to obtain an absolute measure of virulence. The most that can be done is to compare the relative virulence of two or more strains injected simultaneously.