logical changes which inhibit growth. Mother rats 
so treated exhibited retarded growth, as also did 
their young. Similarly, Holzbauer et al. (73) sub- 
jected rabbits to daily electroconvulsive shocks 
beginning at 1 1 and 1 8 days of age. Experimentals 
exhibited a marked retardation of increase in 
weight. Furthermore, after a time weight actually 
declined and terminated in death. Vogt (74) 
demonstrated that a strange, and presumably emo- 
tional experience, elicits adrenal cortical activity. 
She conditioned one group of rats to the procedure 
of having their rectal temperature taken. On the 
sixth day these, and a group of experimentals who 
experienced this procedure for the first time, were 
killed 1 hour following the taking of their rectal 
temperature. There was a more marked adrenal 
activity on the part of the experimentals as revealed 
by a 60 percent drop in the ascorbic acid content 
of the adrenals in the experimentals. The assump- 
tion here is that those rats chronically subjected to 
a mildly disturbing situation learned that the ex- 
perience was not harmful and, therefore, found no 
need to go into the alarm stage of adrenal activity. 
Weininger (75) provides additional insight into this 
question. He gentled one group of Wistar albino 
rats by daily periods of handling and petting be- 
tween 23 and 44 days of age. By 44 days of age 
the gentled rats had gained (161 vs. 141 g.) sig- 
nificantly more in weight than their nonhandled 
controls. This weight differential was maintained 
to time of autopsy at 79 days of age (319 vs. 265 g.). 
To my knowledge no formulation has been for- 
warded as to the psychological basis for such weight 
differentials. Briefly stated, my hypothesis is as 
follows: For the nonhandled rat many of the events 
taking place in the laboratory external to its cage 
were of unknown meaning and were reacted to in 
an emotional way. However, the handled rat 
generalized its learning that a particular event was 
harmless to all other events of unknown meaning, 
and so existed at a low level of emotional reactivity. 
At 79 days of age Weininger subjected these two 
groups of rats to 48 hours of a situation very strange 
to them. They were bound in an immobile state 
for 48 hours on their backs without food. At 
autopsy at the end of this time the nonhandled 
rats exhibited more bleeding points in the gut, 
more damage to the heart, and enlarged adrenals. 
These citations are adequate to indicate that events 
external to the organism and of a nonbiological 
character can generate release of adrenal corticoids 
with concommitant retardation of growth. 
Social interactions can also produce alterations 
in the adrenal of a nature which the other studies 
cited above indicate may produce retardation of 
growth. Crowding in small cages has been the 
stressor producing such changes in house mice (76, 
77, 78) voles (79) and Norway rats (51). Bul- 
lough’s study (76) revealed a reduction of mitotic 
activity by such stressful conditions. Perhaps this 
finding is the key to the retardation of growth in 
animals subjected to chronic stressful events. Ac- 
cording to Blumenthal (81 ) mitotic rate is inhibited 
by hypoglycemia. Thus, growth should be less 
during any chronic “stage of exhaustion” with its 
characteristic low blood-sugar level. 
Similar lines of reasoning have been forwarded 
by Christian (82) and Clarke (80) to explain the 
rapid die-off of populations which have attained 
densities which may be designated as crowded. 
Disturbances in reproductive physiology, including 
malformation of young, and convulsive death of 
stressed hypoglycemic animals (83), were the ave- 
nues by which Clarke and Christian believe stressful 
conditions of life exert control over population 
density. 
There is thus both a logical and a factual basis 
for anticipating retardation of growth whenever 
conditions or events external to the organism 
chronically overtax the adjustive ability of the 
adrenal cortex. Furthermore, social interactions 
form a category of events which may tax adrenal 
physiology. It is this line of reasoning which has 
led me to assume that the observed differences in 
growth from rat to rat in my Towson colony 
primarily resulted from social interactions. Thus, 
when one does not wish to sacrifice his subjects, 
growth rate may be taken as an index of social 
disturbance. 
One must exercise considerable caution in 
utilizing growth rates as indices of social disturb- 
ances when the subjects include both domesticated 
and wild strains of rats. Domestication has pro- 
duced marked alterations in adrenal and growth 
physiology (34) as judged by decrease in size of 
adrenal cortex and thyroid, and by an increase 
is size of the hypophysis. Richter shows that the 
wild Norway rat is highly resistant to direct insults 
on its physiology. The FD 50 dose of ANTU is 400 
limes that for domesticated strains. In comparison 
to domesticated strains wild Norway rats are highly 
resistant to convulsive seizures of either audiogenic 
or magnesium deficient diet origin. However, the 
wild rats are more likely to show deleterious effects 
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