“…In an endeavour to trace their true source McKenzie, Morrison & Lambert (1946) examined hair clippings of cows, swabs of the skin of the udder and teats, soil, faeces, fodder and bedding, with negative results. Thomas & Roberts (1946) found only small numbers in farm water supplies. In the latter two investigations the technique employed consisted of pasteurizing the:samples in a watery medium as distinct from heating in milk.…”