From Russell, W.M.S. and R.L. Burch. 1959. The Principles of Humane Experimental Technique. Methuen, London:
“Chapter 4, THE SOURCES, INCIDENCE, AND REMOVAL OF INHUMANITY; The three chief principles stated…
The Removal of Inhumanity: The Three Rs
We turn now to consideration of the ways in which inhumanity can be and is being diminished or removed. These ways can be discussed under the three broad headings of Replacement, Reduction, and Refinement (Russell, 1957a; cf. also Hume, 1957; Medawar, 1957). An earlier attempt to classify the subject (Russell, 1955) dispensed, like the Mock Turtle, with the advantages of alliteration; but the three modes now considered have conveniently been referred to as the three Rs of humane technique (Russell, 1957a).
Replacement means the substitution for conscious living higher animals of insentient material. Reduction means reduction in the numbers of animals used to obtain information of a given amount and precision. Refinement means any decrease in the incidence or severity of inhumane procedures applied to those animals which still have to be used.”