1. In a series of virulence experiments a comparison was made between the resistance to infection of 551 mice fed on raw and 495 mice fed on pasteurized milk, each dietary being supplemented by a mineral mixture and a whiteflour biscuit. In one set of experiments the mice were inoculated intraperitoneally with about 100 or 1000 living Bact. typhi-murium and observed for a fortnight; in another set they were fed by the mouth with about 100–200 million living organisms of the same strain and observed for 4 weeks. All animals dying during, and all survivors killed at the end of the experiments were bacteriologically examined for evidence of specific infection.

2. In the intraperitoneal inoculation experiments the results obtained with the raw and pasteurized groups respectively were as follows: Proportion of animals dying of specific infection 51·83 and 51·20 per cent; proportion of all animals found to be specifically infected at death or when killed 95·29 and 91·57 per cent; average survival time of animals dying of specific infection 8·06 and 6·93 days. The proportions of animals dying of specific infection when standardized for weight distribution were 55·1 and 50·6 per cent respectively.