The adulteration of London milk and cream in the nineteenth century (and before) is presented in gruesome detail by John Timbs in Curiosities of London (1855):
The adulteration of milk is a pestilential practice. The substances usually employed are water, flour, starch, chalk, and the brains of sheep, oxen, or cows; the brains have been detected with a microscope, shewing the nerve-tubes, their natural size being only about 1500dth of an inch in diameter ; they are rubbed with warm water into an emulsion, and then added to the milk, or in larger proportion to London cream. This is a vile fraud imported from Paris. In Smollett's time (see Humphrey Clinker) London milk was described as chalk and water, with beaten snails for froth; the milkmen of our day have added treacle, salt, whiting, sugar-of-lead, annatto, size, &c. : the sugar-of-lead is most pernicious, being formed into carbonate of lead, which is held in suspension, a little giving a great bulk of water a milky appearance. A never-failing pump, or “cow with the iron tail," is indispensable to a Dairy establishment, to balance the statistics of demand and supply.