“…Any attempt to quantify biological data must be made with the realization that variations occur during the course of a day and that such changes vary from a few per cent to several fold. These diurnal variations are found in such diverse phenomena as metabolic activity (Bahorsky & Bernardis, 1967), motor and e.e.g. activity (Holmquest, Retiene & Lipscomb, 1966;Koella & Czieman, 1966;Mount & Willmott, 1967), and synthetic, enzymatic and catabolic processes (Min, Jones & Flink, 1966;Rapoport, Feigin, Bruton & Biesel, 1966;Civen, Ulrich, Trimmer & Brown, 1967;Wurtman, Chou & Rose, 1967).…”