The Paper by A.C.Nicholls in the October 1954 Journal (p. 724) describes two empirical equations neither of which possesses the first essential of an acceptable strain hardening function, namely that the stress attained in a preliminary straining operation shall become explicitly the threshold stress at which subsequent deformation begins. Eight years of study and the analysis of hundreds of published curves have convinced me that the exponential function put forward in 1948 faithfully reflects the strain hardening process. Far from being empirical, it can readily be deduced from a few simple and credible assumptions, and has counterparts in many branches of physics.