LIGHT AND METABOLISM 15 



the 24 hours and the reversal of the sleep habit. Similarly, the normal 

 phasic swing of the ocular tension is independent of the blood pressure, 

 osmotic changes in the blood, illumination, the time of meals, feasting 

 or fasting, or bodily activity ; the rhythm can only be altered by a 

 complete reversal of the sleep habit established over some time 

 (Raeder, 1925) (Fig. 8). The fact that such rhythms as the diurnal 

 variation in temperature in the new-born infant, or the 24-hour 

 periodicity of activity of the newly hatched chick kept under constant 

 laboratory conditions (Aschoff and Meyer-Lohmann, 1954), are 

 apparent from birth indicates that at any rate some of these fluctuations 

 are fundamental and innate — an environmental influence of biological 

 value which has with time so impressed itself upon organisms that it 

 has become hereditarily transmitted. 



Some of these diurnal variations, however, seem to depend on environ- 

 mental stimulation. Thus the cyclic variation in the eosinophil count of mice 

 was found by Halberg and his associates (1954) to be abolished by the enucleation 

 of both eyes, although it partially returned some 5 months after blinding. The 

 rhythm of diurnal activity of the minnow, Phoxinus, is said to be reversed on 

 blinding (Jones, 1956). In man the variation in eosinophilia depends to some 

 extent on activity (Halberg et al., 1953), and illumination has a subsidiary 

 influence (Appel and Hansen, 1952 ; Landau and Feldman, 1954). 



The same rhythms in general activity are seen in Invertebrates, 

 among which Insects provide some of the most dramatic examples (see 

 Welsh, 1938 ; Wigglesworth, 1953). The habit of nocturnal activity 

 and diurnal catalepsy show^l by the stick-insect, Dixippus, for example, 

 persists unchanged for some days in permanent darkness or in reversed 

 illumination (Steiniger, 1933), a daily rhythm which applies to such 

 activities as defsecation and ovij^osition (Kalmus, 1938). The same 

 general tendency is seen in many other species.^ The rhythm may, 

 indeed, be acquired in the larval stage in response to diurnal changes 

 of light, persist through the pupal stage and determine the activity in 

 the adult. 2 A metabolic rhythm in which the CO2 is higher (some- 

 times by 30%) during the night even although the animal is kept in 

 constant darkness is seen in Crustaceans.^ A similar diurnal rhythm 

 of the opening and closing of the valves of the clam, Venus mercenaria, 

 persists under laboratory conditions of constant illumination ; it is 

 interesting that in this case there is also a persistent tidal rhythm and 

 the interaction of the two produces a lunar cycle (Bennett, 1954). A 

 similar phenomenon whereby an endogenous tidal rhythm displaces 



^ It is seen in some forest insects (Lutz, 1932 ; Park and Keller, 1932), mayflies 

 (Harker, 1953), cockroaches (Gunn, 1940 ; Mellanby, 1940 ; Marker, 1954), millipedes 

 (Park, 1935), and other species. 



2 In Leptinoiarsa — Grison (1943). 



^ The crab, Carcinus — Menkes (1952) ; the woodlouse, Oniscus — Cloudesley- 

 Thompson (1952). 



