ORIGIN AND AIMS OF THE STUDY 
1 . General Background 
Dr. Curt P. Richter (7) showed that rats are 
capable of choosing nutritive substances and 
avoiding harmful ones. One of his hypotheses 
was that there was a relationship between the taste 
of substances and their nutritive value. While 
investigating this hypothesis he (2) found that 
phenyl thiourea was lethal to rats in minute 
quantities. Although domesticated rats normally 
took sufficient food containing phenyl thiourea to 
be lethal, field tests on wild populations of rats 
were unsatisfactory in producing significant kills. 
Wild-caught rats transported to the laboratory 
demonstrated marked ability to avoid food con- 
taining phenyl thiourea, choosing, instead, un- 
poisoned food. There followed a search for a 
toxic thiourea derivative which lacked the bitter 
taste of phenyl thiourea. The result of this search 
led to the selection of Alpha-Napthyl Thio-Urea 
(ANTU) as a suitable rodenticide. These in- 
vestigations occurred at the beginning of World 
War II when the normal sources of several pre- 
viously proven rodenticides were cut off. 
There developed a cooperative program of rat 
control and research between the city of Baltimore 
and the Johns Hopkins University (3). In the 
normal course of block by block treatment with 
ANTU, 50 to 85 percent reductions were regularly 
obtained. Depending upon the extent of reduc- 
tion of the original population, recovery to the 
prepoisoning level took between 1 5 and 44 months 
(4). This necessitated repeated applications of 
ANTU poison. It soon became apparent that, 
whereas poisons played an integral part in rat 
control, they were no panacea. The continued 
support of the International Health Division of the 
Rockefeller Foundation to the Johns Hopkins 
School of Hygiene and Public Health enabled a 
broad approach to the problem. As a result, 
mainly through the efforts of Dr. David E. Davis, 
the emphasis of technical procedures in rat control 
turned from poisons to environmental control. 
The understanding of the philosophy underlying 
this shift in the emphasis requires an appreciation 
of the rat ( Rattus norvegicus ) as an organism. We 
must understand how they manage to live in close 
association with others of their kind; and how as 
individuals or as groups conditions of the environ- 
ment modify the satisfaction of those basic require- 
ments necessary to survival. 
The study presented in this publication attempts 
to provide this understanding. In addition, the 
findings will point to the usefulness of the rat in 
investigating other topics which have little or no 
relationship to the problem of rat control. The 
author was given complete freedom to make such 
investigations as he thought would be most 
productive in revealing the nature of the rat’s 
biology. At the time he joined the staff of the 
Rodent Ecology Project, there was one fact amply 
documented by Drs. John T. Emlen, Jr., and 
David E. Davis and Mr. Allen W. Stokes. This 
was that each city block where rats were poisoned 
would, following termination of poisoning, ulti- 
mately arrive at a stable population level closely 
approximating its original prepoisoning level. 
This posed the general problem of why the popula- 
tions leveled off, and furthermore, why two blocks 
of approximately the same size would have 
different stable levels or carrying capacities. 
As an initial probing into this problem the author 
(5) introduced into a stable population a number 
of alien rats caught from distant blocks. The 
number of aliens was approximately 65 percent 
of that of the resident population. Following 
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