Microbic Virulence and Host Susceptibility

One of us (Webster) has shown that the general non-specific resistance of mice bred at the Rockefeller Institute includes important elements associated with heredity and that, by selective breeding, the general resistance of a mouse population may be altered? We wish now to describe some experiments which demonstrate the effect of diet on host susceptibility to infection and intoxication. For some years the mice in the breeding room of the Rockefeller Institute have received a diet consisting of a daily ration of baker 's bread soaked in fresh pasteurized Grade B milk warmed to at least 60-70°C., supplemented by two weekly feedings of an oatmeal and buckwheat mixture and one weekly feeding of dog biscuit. On this diet the animals thrive and breed well and are to all appearances in excellent health. It was thought desirable to compare the resistance of these mice with that of similar mice raised on some other stock diet in general use. Consequently, a so called normal diet for mice and rats, advocated by E. V. McCollum, was chosen 2 which consists of the following ingredients: wheat 67.5 per cent, casein 15 per cent, milk powder 10 per cent, NaC1 1 per cent, CaCO~ 1.5 per cent, and butter fat 5 per cent. This diet was prepared by mixing the finely ground whole wheat with the inorganic salts, casein, commercial milk powder, and the clear fat from melted sweet butter. Small quantities were continually avail-