For the turtle Pseudemys scripta the temperature characteristics for excitability of the response to visual flicker are found to be independent of flash frequency F, flash intensity I, and proportion of light time in the flash cycle. The maximum F to which the flicker response contour (F vs. log I) rises, and the abscissa of its inflection, are rectilinear functions of the percentage light-time in the flash cycle, but µ for 1/Iat any flash frequency is the same with different values of the percentage light-time (10 to 90 per cent).
These facts, together with the properties of the variation of the critical intensity, objectively demonstrate the essentially simple or unitary character of the controlling events in the mechanism governing the excitability. They also provide a means of further illustrating a procedure whereby certain statistical factors in the performance of a population of units may be analytically separated from excitability properties common to all of the individual units. In particular, it is of general significance that it can be seen how it is possible for biologically exhibited frequencies or rates of performance to provide simple and physically significant relations to temperature, despite the fact that this performance may involve, almost inevitably does involve, the integrated actions of many individual units.