the lunar periodicity and also prevented it from 
regaining its timing with the actual moon cycle. 
This effect of continuous high social tension on the 
lunar activity rhythm is quite analagous to the 
effect of continuous light upon the endogenous 
24-hour activity rhythm of nocturnal animals or of 
continuous darkness upon the endogenous 24-hour 
rhythm of diurnal animals (13). In these instances 
the continuous presence of the inhibitory condition 
prolongs the onset of activity and thus increases the 
length of the activity cycle to something greater 
than 24 hours. 
When only the total amount of activity occurring 
through the North and South Passages was con- 
sidered, it was possible to calculate for each day 
the percentage of the total activity occurring 
through each of these passages. These calculations 
are shown as reciprocal curves in figure 94 through 
the period that data were available. We shall 
first examine the relative intensity of activity of the 
more dominant rats utilizing the South Passage 
(No. 5). During the 3 winter months of Novem- 
ber 1947 through January 1948, when factors 
influencing increased competition were at a mini- 
mum, there was an increase in activity during 
times of low intensity of moonlight and a cor- 
responding decrease in activity during periods of 
increased moonlight. These correlations between 
activity and moonlight were quite clear for five 
out of the six moon phases over this period. Since 
this inverse relationship between nocturnal light 
intensity and activity occurred for the more 
dominant rats, it was concluded that this was the 
basic relationship where other conditions modi- 
fying intensity of activity are absent. 
On the other hand, the relative intensity of activ- 
ity of the lower-ranking rats, utilizing the North 
Passage (No. 7), showed the opposite relationship 
to nocturnal light intensity. The interpretation 
placed upon this was that there was sufficient 
social interaction between these two groups of rats, 
that the augmentation of the activity of the more 
dominant rats inhibited that of the more submissive 
ones. These reciprocal rhythms exhibited by rats 
of opposite rank, which appear to be correlated 
with the phase of the moon, are rhythms of relative 
intensity only. Whatever effect lunar luminosity 
may have on activity, it may be masked by other 
conditions which modify intensity of activity. 
That this is so may be seen in figure 95 in which the 
trend of the actual number of passages through the 
South Passage is graphed. 
During the winter months (November, Decem- 
ber 1947, January 1948, and February 1949 as 
shown in fig. 94) there was a consistently greater 
amount of activity through the North Passage, 
even at times when there was a relative inhibition 
of activity by the rats involved. This is interpreted 
as being a direct reflection of the fact that more 
adult rats usually inhabited the north side of the 
pen. This is just another line of evidence to that 
presented later in the paper, that socially lower 
ranking rats are subjected to conditions which im- 
pose a greater frequency of contacts between 
individuals. 
As the 1948 breeding ensued there was a dis- 
appearance of the apparent correlation between 
the lunar cycle and the relative amount of activity 
through the North and South Passages. Likewise 
the consistently greater amount of activity through 
the North Passage disappeared. It is not possible 
to offer a rational explanation for the near equality 
of activity through these two passages during 
February 1948, the beginning of the breeding 
season. However, those fluctuations, which oc- 
curred during March through June 1948 (fig. 94) 
were apparently dependent upon the number of 
lactating females and the number of weaned 
young present in the north and south sides of the 
pen. Coincident with the presence of three to 
four lactating females and then their 30-weaned 
young on the south side of the pen there was 
a period of 3 weeks in March and April 1948 during 
which there was for the first time a greater amount 
of activity through the South Passage than through 
the North Passage. This relationship between 
intensity of activity and place of entry into the 
Food Pen changed twice more during April to 
June 1948. First a group of 19-weaned young 
from the north side of the pen altered the balance 
in density. Then a second group of weaned 
young from the south side of the pen made their 
appearance, and they produced a second period 
of greater activity through the South Passage 
(No. 5). Because of the greater reproduction 
occurring on the south side of the pen one might 
have anticipated that at future dates there would 
have been a maintenance of greater activity 
through the South Passage. However, by Febru- 
ary 1949 there was again nearly twice as much 
activity through the North Passage as through the 
South Passage. This was a result of the fact the 
many of the young born on the south side of the 
pen were forced to migrate (see table 30) to the 
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