human poisoning, oxygen should be administered but no fluids should be 
given either by mouth or intravaneously." 
How Interest In ANTU As Rodenticide Arose 
Dr. Richter says that interest in ANTU arose directly from studies 
on the self-selection of diets, which showed that rats are capable of 
choosing nutritive substances and avoiding harmful ones. This ability to

make beneficial dietary selections was found to be lost when taste nerves

were completely severed. It was, therefore, concluded that some connec- 
tion exists between the taste of substances and their nutritional or 
toxic values. 
"To test this theory, the toxicity of various bitter substances was

determined," he says. "One very bitter substance which was considered

non-toxic was phenyl thiourea, also known as phenyl thiocarbamide. Since

the observation of Fox in 1931 that, while this compound tasted very bitter

to most people there were some who could not taste it at all, phenyl 
thiourea has been widely used for research in the fields of genetics and

sensory perception." 
Dr. Richter says that following the usual method of testing taste 
ability in human beings with phenyl thiourea, he and his associates placed

a few crystals on the tongues of six rats. To their surprise, all six were

found dead the next morning. 
Wartime Shortages of Staple Rat Poisons Accelerate Research 
"Shortly before the entry of this country into the war it was real-

ized that we were in a very vulnerable pqsition with respect to the con-

trol of rats and rat-borne epidemics," he explains. "Red squill,
the 
staple rat poison, was no longer available in adequate amounts because 
the Axis powers held the sources of supply along the Mediterranean sea- 
board. Other possible poisons were eliminated by critical requirements 
or potential hazards in use. 
"The wide and prolonged use of phenyl thiourea for taste and inher-

itance tests without any accidents indicated that it probably does not 
have any toxic action on man. This probability, coupled with its high 
toxicity to rats, make it seem an excellent candidate as a substitute for

red squill. Through the interest of Colonel Perrin Long, at that time 
chairman of the Committee on Chemotherapeutic and Other Agents of the 
Division of Medical Sciences of the National Research Council, a grant was

given this laboratory to test phenyl thiourea as a rat poison and also to

determine which baits would serve most effectively in its use. The work 
was begun January, 1942." 
Du Pont Supplies Over 200 Compounds for Evaluation 
In his paper, Dr. Richter outlines the successive steps in the 
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