Letters from Charles Claud Twort Letters to Karl Pearson containing background details and methodology to experiments on the carcinogenic effect of oils and tars used in the cotton industry on mice; enclosing census data on mice kept in their animal house, and tabulated data on the time it took the tumour to arise according to the mouse colour; about the source of mice used in experiments and any congenital defects; enclosing a record of tumours in 5000 mice painted with shale oil from a 1918 experiment; and about the change to malignancy in 4000 tumour mice, and death rates. Jun 1931 - Sep 1931