RHYTHMIC NATURE OF ANIMALS AND PLANTS—BROWN 403 
SUN 
fe) 
ZENITH TIME 
METABOLIC RATE 
METABOLIC RATE 
DAYS OF MONTH 6AM NOON 6 PM 
Ficure 7.—A, The variation in average metabolic rate in the potato with time of the lunar 
month. B, The change in form of the average daily metabolic fluctuation with day of 
the month. 
at the time of third quarter. The rate of metabolism was 20 percent 
higher at third quarter than at new moon. There was also a monthly 
cycle in the form of the daily cycles. As seen by the dotted curve in 
figure 7B, the daily cycles were depressed during the morning hours, 
at the time of new moon, and, as shown by the solid line, quite sym- 
metrical and high, with a maximum at noon, at the time of the third 
quarter. The sun is, obviously, always at its highest point in the 
sky at noon. The time of day the moon is highest depends on the 
time of month. Over full moon, it is midnight; over new moon it is 
noon. These changes in the form of the daily cycles through the 
month seem logical if we think of the sun and moon having qualita- 
tively the same effect on metabolism, the maximum accelerating action 
of each on metabolism occurring about 6 hours later than the time it 
reaches its zenith in the sky. 
An annual cycle in the form of the daily cycles was also found to 
exist in constant conditions. The average monthly values for two 
years of study are shown in figure 8A. The cycles were lowest in 
amplitude in January and February, and highest in September, Oc- 
tober, and November during both years. There was also an annual 
cycle in general metabolic rate in the constant conditions (fig. 8B). 
The highest rate occurred in May, and was about twice that seen in the 
lowest month, October. 
Collectively these facts provide incontrovertible evidence that even 
when we have thought we have excluded all forces influencing the 
living things, there is, nonetheless, cyclic information, unquestionably 
