Abstract
Dr. Roger Berry was kind enough to send to me a copy of the article on Excess Late Subcutaneous Fibrosis after Irradiation of Pig Skin Consequent Upon the Application of the NSD Formula. I feel that the following comments are justified. (1) The value of 0·33 as the regression coefficient for the isoeffect line when log dose is plotted against log time has considerable basis in many previous publications. This is used as a basis which, suitably partitioned according to the NSD concept for the first time, made possible for the first time separation of the effects of fractionation and of time (Ellis, 1966; 1968; 1971).

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