Very little that was needed for this study was available from catalogs at the time. In order to study bovine enteroviruses, it was understood that I must produce primary bovine kidney cell cultures. Balanced salt solutions (Hanks' and Earle's) were produced from individual salts, glucose, and deionized water. Medium was either of the salt solutions plus 0.5% lactalbumin enzymatic hydrolyzate. These were sterilized by autoclaving. Growth medium required addition of 5% bovine serum, and maintenance medium had 2% bovine serum. Bovine serum was produced by collecting blood at a slaughterhouse, allowing it to coagulate, and sterilizing the expelled serum by filtration through an asbestos-mat Seitz filter. The kidney to be cultured was collected as aseptically as possible from a freshly slaughtered animal. Only the cortex of the kidney was suitable for culture; since the bovine kidney is lobular, it was necessary to dissect the cortex individually off of each lobe of the kidney. These pieces were minced and mixed with trypsin solution, in an Erlenmeyer flask with a magnetic stir bar. Periodically, cells that had been freed were harvested and sedimented gently in a centrifuge; fresh trypsin solution was added to the flask until enough cells had been harvested to produce a week's cultures. Cultures were grown principally in 4-ounce (*100 ml) prescription bottles closed with white rubber stoppers (Cliver and Bohl 1962a) . These were highly compatible with the cells, but required rigorous cleaning if they were used more than once. Unevenness in the glass limited visibility with the microscope and caused at least some problems with distribution of the cells when the culture was seeded and with distribution of virus inoculum during plaque assays. Semisolid overlays for plaquing combined double-strength growth medium with double-strength agar solution and 0.5% neutral red. When the agar had solidified, the cultures were incubated cell-sideup in darkness at 37°C and observed for plaque formation at approximately 2-day intervals. Further details of how individual enterovirus strains were isolated and how quantitative neutralization tests were performed have been published elsewhere (Cliver and Bohl 1962a, b) .