diurnal. Hoarding, more appropriately designated 
simply as storage, is a behavior with many nuances, 
to whose origin many conditions contribute, when 
it develops in the context of a socially structured 
population. Likewise, experimental studies of the 
rat, covering such areas as perception, motivation, 
learning, and emotion, all of which have been 
intensely pursued in the laboratory, promise to 
become much more fruitful when further pursued 
with respect to the conditions which foster social 
interaction and development of culture. Only 
after completion of such complex studies can we 
hope to arrive at an approximate evaluation of the 
rat as a social organism. 
The remaining portion of the discussion section 
of this monograph will suggest, or fill in, some of 
the obvious gaps required to describe the sociology 
of the Norway rat. 
4 . The Learning of Social Adjustments as 
a Factor in Determining Physiological 
Disturbance and Social Mobility 
Barnett (57) has investigated competition among 
wild Norway rats in 1 -cubic-meter enclosures in 
which the inhabitants were marked for visual 
identification. Several males which were simulta- 
neously introduced might live together for as long 
as 22 months without mortality or rarely ever any 
injury to one another. However, the introduction 
of another male leads to his attack by the resident 
males. Barnett concludes that this latter is evi- 
dence of territorialism. Such a conclusion is prob- 
ably not warranted. The study cage was much 
smaller than the normal range of a rat, nor was 
there the opportunity of sustained exclusion from 
a given space. When these two conditions are not 
fulfilled we are not justified in speaking of territo- 
riality but merely in ter individual antagonism. 
From this latter viewpoint Barnett’s observations 
become important. 
The stranger introduced into the group frequendy 
died, not from wounds, but from an undetermined 
physiological breakdown. This raises a very inter- 
esting question: Why do several rats who are 
strangers to each other make a satisfactory adjust- 
ment when simultaneously placed in a confined 
space in contrast to the inability of another strange 
rat to make a similar adjustment when introduced 
into the group at a later date? Contact rate can- 
not be the cause. There is only a 25 percent 
increase in contact rate per rat from a group of 5 
to one of 6. No substantiated explanation of this 
important question may be made. However, I 
wish to suggest a plausible hypothesis, which is 
amenable to experimental verification. 
It has been shown by Marx (52) that rats who 
have learned a maze exhibit a declining ability to 
retain this learned behavior as more and more 
different types of mazes have to be learned between 
acquisition of the learning of the first maze and the 
later date at which they are tested for its retention. 
In other words, interpolation of different but simi- 
lar learning tasks mutually interfere with each 
other. Development of a hierarchy or similar 
system of social adjustment among a group of rats 
who are strangers to each other requires learning. 
Furthermore, one would suspect that the rate of 
acquisition of a learned adjustment between any 
two rats is inhibited by the interference of learning 
adjustments with other rats. In the early stages 
of this slowed down social learning each rat should 
serve as a relatively unconditioned stimulus for 
the other rats. Therefore, contact between any 
two rats should produce only a mild emotional 
response and physiological disturbance. Physio- 
logical adjustment, such as increase in adrenal 
size, should be able to keep pace with the gradual 
increase in intensity of interaction as social learning 
proceeds. Thus, at the termination of hierarchy 
formation each rat’s physiology should have 
achieved a state capable of coping with the inten- 
sities of interaction then existing. Barnett showed 
that such physiological accommodation actually 
took place. During the initial contacts of the first 
2 days among members of the group being formed 
there was depletion of the sudanophilic material 
of the adrenal cortex (Selye’s alarm reaction), 
following which there developed a stage of increase 
in adrenal size with maintenance of sudanophilic 
content (Selye’s stage of resistance). At the time 
of the introduction of another rat each of the resi- 
dent members of the group are involved in only 
one learning situation, that directed toward the 
stranger. Thus, the intensity of action of each 
group member toward the stranger might be desig- 
nated as 1, or a total intensity of jV, in contrast to 
the relative intensity of 1/jV-l characteristic of 
each interaction while developing the hierarchy. 
This means that a strange rat introduced into an 
established group of N rats receives N times the 
intensity of action that characterized the group 
during its formation. If this formulation ap- 
proaches correctness, it is small wonder that Barnett 
259 
