observed the strange rat dying from physiological 
exhaustion within a day or two. According to 
Selve’s formulations, the terminal stage of exhaus- 
tion must have been reached, without the oppor- 
tunity 7 for the intermediate stage of resistance 
intervening after the initial stages of alarm reaction 
At the time of introduction of a stranger even the 
members of the established group should be under 
a heightened emotional state. Dr. Allan Dittmann 
of the National Institute of Mental Health informs 
me that a similar situation is characteristic of groups 
of delinquent children which he is studying. The 
group is composed of six boys. From time to time 
one boy is released to go home and a replacement 
added. Not only does this new boy have a hard 
time at first, but also the group as a whole is set 
into turmoil for a day or two following his admis- 
sion. 
With this background we are in a better position 
to appreciate the origin of the stress existing in many 
of the local colonies of rats in my Towson popula- 
tion. Most males and a few females are ejected or 
at least depart from the more stable socially higher 
ranking colonies. These individuals are attracted 
to and join seme other, but socially lower ranking 
group. As a consequence this whole group is upset 
and the intruder in particular must receive partic- 
ularly intense interactions. The intruder is some- 
times able to join the group. But this increases 
the size of the group. And since groups tend not to 
exceed 12 individuals pressure builds up to exclude 
some member. When this happens there is a 
drifting rat which usually attempts to join another 
group. Since groups attempt to exclude intruders, 
a drifter should find easiest access to those groups 
which have the most recent additions of other 
drifters, because they will have the less crystalized 
social structure. This process predicts a gradient 
among the colonies in a population such that at one 
extreme membership is highly prolonged and rela- 
tively unchanging, while at the other extreme 
membership is temporary, and the individuals 
represent many places of birth. A reexamination 
of table 57 supports this formulation. 
Mobility, in the sense of frequency of change 
of rr-idence and group membership, is negatively 
correlated with attainment and maintenance of 
body weight and with reproductive performance. 
All evidence indicates that resultant changes in 
social status are downward. 
5 . Events and Conditions Relating to the 
Maternal Period of Life 
In the following seven sections there are presented 
results of several lines of investigation, as well as 
formulations derived from them. These provide 
insight into the field studies and indicate some pro- 
blems toward which future study of the maternal 
period of life may be directed with profit. 
A. Stress Induced by Electroconvulsive Shock in Rela- 
tion to Adrenal Function, Growth, and Maternal Be- 
havior. The studies of Rosvold and his associates 
on rats (53 to 58) provide valuable insight into 
how stressful experiences may have produced some 
of the physiological and behavioral aberrations 
apparent in the present study. Electroconvulsive 
shock (ECS) was the stressor. Chronic ECS pro- 
duced adrenal hypertrophy, and an increased 
output of ascorbic acid. These effects on the 
adrenal were apparently mediated by way of the 
hypothalmus and the anterior pituitary. Futher- 
more, these effects on the adrenal by ECS were 
produced only when behavioral changes simulta- 
neously occured. Thus, adrenal and behavioral 
changes accompany ECS alone but not ECS plus 
anesthesia. On the behavioral side learning and 
retention of a learning is impaired in the ECS 
stressed rats; nest building is impaired or even 
inhibited for at least 10 days post ECS treatment 
in males and for a much longer time in lactating 
females. Females who received ECS treatment 
for 15 days beginning within 84 hours following 
conception resorb many embryos. In these 
females nest building and retrieving of young is 
usually impaired throughout lactation although 
the young reared equaled controls at weaning. 
These maternal behaviors show residual impair- 
ment even with a second litter born 47 days after 
shock treatment. If the mother received ECS 
treatment during the first 1 5 days following partu- 
rition, growth of the young was inhibited both 
during this and the following 15 days during 
which weight data were recorded. Furthermore, 
rats who received 10 days of ECS beginning at 
170 days of age exhibited an inhibited growth 
during the 23 post ECS days. To the extent 
that the ECS stressor and the social interaction 
stressors are equivalent it is logical to believe that 
the inhibition of growth, conception, burrow 
building, nest building, and maternal behavior 
recorded for the wild rats in my 100-foot square 
260 
