LIGHT AND METABOLISM 13 



Klebs. i'^ora, 11-12, 128 (1918). Tournois. C. R. Acad. Sci. (Faris), 155, 



Lang. Ann. Rev. Plant Physiol, 3, 265 297 (1912). 



(1952). Vegis. Sijmbolae Botan., Upsalienses, 14, 



Loeb. Pfliigers Arch. ges. Physiol. , 54, 81 1 (1955). 



(1893) ; 56, 247 (1894). Verworn. Psychophysiologische Protisten- 



Loehwing. Proc. Soc. exp. Biol. Med., 37, studien, Jena (1889). 



631 (1938). Wareing. Ann. Rev. Plant Physiol., 7, 



Melchers. Biol. Zhl., 56, 567 (1936); 57, 191 (1956). 



568 (1937). Wassink,SluysmansandStolwijk.Xonin^-/. 



Parker, Hendricks and Borthvvick. Botan. tied. Akad. Wetens. Proc, 53, 1466 



Gaz., Ill, 242 (1950). (1950). 



Schubeler. A'«?(/re (Lond.). 21, 31 1 (1880). Wassink and Stolwijk. Ann. Rev. Plant 



van Senden. Biol. Zbl., 70, 537 (1951). Physiol., 7, 373 (1956). 



Smith, F. Meld. Norg. LandbrHoisk., 12, Withrow, Withrow and Biebel. Plant 



1 (1933). Physiol., 18, 294 (1943). 



PHOTOPERIODISM IN ANIMALS 



DIURNAL METABOLIC RHYTHMS are equally remarkable among 

 animals, for the cycle of day and night with its rhythm of changes in 

 illumination, temperature and other environmental factors has so 

 impressed itself upon living creatures in the course of their palaeonto- 

 logical development that many of their metabolic processes vary with 

 a corresponding periodicity, synchronized as it were by an internal 

 physiological clock. 



These physiological rhythms have received much study and have accumu- 

 lated a considerable literature. ^ Among Mammals, including Man, the periodicity 

 of sleep and activity is the most obvious, ^ possibly a survival of the nocturnal 

 reduction of nervous activity in primaeval Amphibians. Most animals are 

 diurnally active ; but in nocturnal animals the cycle of activity is reversed.^ 

 A similar cyclic variation is seen in bodily temperature. ^^ In Man the temperature 

 through the day is higher than at night, but considerable variations occur in 

 the characteristics of the curve ; in some individuals the peak is in the morning, 

 in others in the afternoon and in others at an intermediate .time. The blood 

 constituents show a variation affecting the haemoglobin, haematocrit readings and 

 plasma proteins,^ while the variation in the eosinophil count is dramatic ; in 

 Man, in the morning there is an eosinopenia* ; in nocturnal animals such as 

 mice the count is high in the morning and low in the early hours of the night.' 

 A similar rhythm acting independently of the intake of fluid affects the urinary 

 output, involving not only the excretion of water but also that of electrolytes 

 (Na, K and chlorides, etc.) and urea which persists even if the 24-hour day is 

 disrupted for periods up to 6 weeks. ^ Even more fundamental cellular processes 

 are involved such as mitotic activity which is maximal in the rest-period at 



» See Kleitman (1949), Menzel (1952), Halberg (1953). Marker (1958). 



2 See Kleitman (1939). 



3 Rat— Richter (1922), Browman (1937) ; wood rat— Colton (1933) ; vole— Davis 

 (1932) ; hedgehog— Herter( 1934) ; mice— Achelis and Nothdurft (1939), Aschoff( 1952), 

 Kowalski (1955) ; wikl mice — Johnson (1926). 



« See Kleitman et al. (1937-38), Kleitman (1949), Halberg et al. (1953). 

 « Renbourn (1947). 

 * von Domarus (1931). 

 ' Halberg and Visscher (1950-52). 



« Gerritzen (1936-40), Mills (1951), Mills and Stanbury (1952), Mills et al. (1954), 

 Lewis et al. (1956), Lewis and Lobban (1956). 



