at the new location revealed that the rats were able 
to detect it immediately. It seems as though the 
perception of a stimulus such as this is not specific, 
but embodies other objects in the environment. 
If the food hopper had been repeatedly moved 
from one location to another one could determine 
if rats can develop the behavior of immediately 
responding to this stimulus irrespective of the other 
stimuli in the surroundings. Even though this 
might prove to be the case, the initial observation 
of the importance of location remains relevant, 
since occasional changes rather than repeated 
changes are the more customary sequence of events 
in the life of a rat. 
In a study of the effect of DDT dusting on the 
prevalence of typhus antibodies in rats ( 67 ) DDT 
dust was placed across rat runways and at access 
openings in buildings. Reuse of runways can be 
determined by presence of tracks through this 
insecticide dust. “Whenever possible, rats aban- 
doned old well-established runways in favor of 
new undusted runways.” There was also evidence 
of rats moving out of dusted areas into surround- 
ing undusted areas, with return to the home sites 
only after the surrounding area was also dusted. 
These behaviors of the wild Norway rat suggest 
the following generalization: Rats develop an 
habituation to particular stimuli and to pattern 
relationships among them, and thus those responses 
may be expressed which immediately lead to satis- 
faction of some drive. Any change in the normal 
stimuli impinging upon the rat interferes with 
elicitation of the appropriate response by engen- 
dering some of the physiological changes associated 
with Selye’s ( 18 ) General Adaptation Syndrome. 
Alleviation of these physiological changes and re- 
sumption of a situation where responses are appro- 
priate to existing stimuli can only be made by 
avoiding the place where the new stimuli occur 
and by returning to the burrow or to other places 
in the environment where such changes have not 
taken place. 
Psychologists [e.g. (95); (59)] have dealt with 
essentially the same phenomenon with domestic 
breeds of the Norway rat, but in situations which 
preclude complete avoidance of the new stimuli. 
1 he most widely used test situation is that of the 
“open field.” In this test rats which have pre- 
viously lived in the confines of a small cage are 
placed in the center of a much larger cage. Avoid- 
ance is permitted only in the sense that retreat to 
the peripheral wall allows a contact response simi- 
lar to that previously experienced in their home 
cage. Urination, defecation, and excessive groom- 
ing are the outward manifestations of the stress 
experienced by such rats. Any new situation that 
cannot be avoided elicits similar responses. In 
the absence of definitive experiments one is led 
to infer that the ability of free-ranging rats to avoid 
strange stimuli reduces the frequency of such 
marked physiological changes. 
In the section, “Social Stress and Proneness to 
Enter Traps”, (pp. 95 to 99) it was pointed out 
that socially low-ranking rats tended to enter traps 
more frequently than did their higher ranking 
associates. Chitty and Southern [( 31 ), p. 317] 
cite an observation which confirms my observa- 
tions that low-ranking rats exhibit a reduced 
avoidance of strange or disturbing situations: 
“Other populations have contained a proportion 
of rats that would come out for token baits in the 
afternoon, while their fellows refused to move out 
from cover. These ‘ bolder’ rats were frequently 
attacked upon their return from the wheat, the 
younger ones sometimes being thrown over on their 
backs, and the wheat removed into the jaws of 
the assailants.” Presuming that these observations 
are typical and represent examples of a general 
principle, three hypotheses may be forwarded to 
explain the origin of reduced avoidance of emo- 
tionally disturbing situations by rats which have 
experienced marked social stress from their 
associates: 
1. The situation is actually less emotionally 
disturbing to them. 
2. Perception is impaired; that is they are less 
able to discriminate between noxious and 
favorable stimuli. 
3. They actually seek out situations which pro- 
duce emotional disturbance; that is emotional 
disturbance has embodied in it the charac- 
teristic of a reward. 
Hypothesis 2 is merely a special case of why 
hypothesis 1 might be true. The only evidence 
that I am aware of negates these two explanations. 
Seitz (59) has reared domestic rats in litters of 
sizes 6 and 12, and isolated the members at 
weaning. There was more competition among 
larger litters for nursing opportunity. When 
placed in an open field the members of larger litters 
defecated more and also walked much less about 
the field. These .data suggest that rats who have 
experienced unfavorable social interactions are 
actually more emotional in a strange situation. 
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