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Correspondence

Strangeways Research Laboratory, Cambridge

This excerpt was created in the absence of an abstract.

The contribution of Porter and Berry (1963) to this interesting correspondence might be interpreted to imply that Hewitt and Wilson (1963) were putting forward a two-parameter model for interpretation of the results of radio-therapy. This, alas, is not so; the model involves at least four parameters—D₀, n, the oxygen : nitrogen sensitivity ratio m, and the fraction of cells in the tumour that are anoxic, which I shall call f. This last quantity is at least as little amenable to experimental investigation in patients as the host resistance postulated by Cohen (1963), and by assigning appropriate values and assuming that—as may well be the case—f changes during a course of treatment, these parameters can equally well be manipulated so as to explain almost any set of observations. Host resistance is not the only deus ex machina.