Armstrong – Table of Contents

When he received the Lansing brain and spinal cord material in August 1937,
Armstrong sought previously unused rodent species in which he would try to adapt
poliovirus. On November 8, 1937, he received several species of rodents, including a
limited number of cotton rats (Eastern cotton rat, Sigmodon hispidus hispidus), from Dr.
A. Packchanian, an investigator at the National Institutes of Health. He inoculated
monkey-passaged infected nervous tissue into the brain, nose and abdomen of a limited
number cotton rats. A few animals developed limb paralysis after prolonged periods but
Armstrong could not passage the infection further through the cotton rats. He also had a
limited supply of the rats, and he stopped further attempts at passage after the first few
months of 1939. He decided to try again during the polio season of 1939 (23) after he was
able to accumulate more animals. This time he was able to infect rats consistently in
serial passage. With the fourth rat serial passage tissue he was able to produce typical
poliomyelitis in monkeys. The virus seemed to be gaining virulence with successive
passages in rats.
After the successful establishment of polio in the cotton rat, Armstrong utilized
this new tool to explore whether monkey antisera derived from various infecting polio
strains, including some isolated by Armstrong, were able to neutralize the Lansing strain
(24). He found that two of the antisera he tested neutralized the Lansing strain and one
did not. This result was consistent with the belief, extant since the early 1930s, that there
was more than one immunological type of poliovirus.
Armstrong also realized that, in order to gain more knowledge of the
epidemiology of poliomyelitis, he would need another laboratory host available in
unlimited quantities to test the immunologic and serologic status of large population