By means of differential ultracentrifugation a macromolecular fraction can be isolated from stools of normal children and of patients with poliomyelitis (1). When obtained from normal stools, these preparations are non-pathogenic for monkeys. When isolated from stools of human patients infected with poliomyelitis, they produce poliomyelitis in rhesus (Macaca mulata) monkeys. In view of the successful application of the electron microscope to the determination of the sizes and shapes of viruses (2), it became desirable to examine such stool concentrates in this instrument. This report presents a preliminary account of studies of such fractions which have been made at Camden, N. J., and at Stamford, Conn.

In March, 1942, samples from several extracts of human stools were prepared by isolating in the ultracentrifuge that fraction which is sedimented by spinning at 39,000 rpm (about 107,000 times g) for 60 min but is not sedimented at 18,000 rpm (about 20,000 times g) for 20 min.

1

Aided by a grant from the National Foundation for Infantile Paralysis, Inc.

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