In 1955, American investigators Carlton Schwerdt and Frederick L. Schaffer crystallized the polio virus. This was the first animal virus to be obtained in crystalline form. (The first plant virus, tobacco mozaic virus, had been crystallized in 1935 by Wendell M. Stanley.) Each virus crystal is composed of many thousands of virus particles. Virus preparations pure enough to crystallize usually provide the best material for chemical studied. This was used to split the polio virus into infectious and non-infectious parts. Their research laid the groundwork for the polio vaccine.(Reference: Proc. Natl. Acad. Sci. 41:1020-1023) Jonas Salk: Beyond the Microscope, by Victoria Sherrow. - book suggestion.