IMPROVED POCK COUNTING METHOD FOR THE TITRATION OF ROUS SARCOMA VIRUS IN EMBRYONATED EGGS

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Abstract
Enumeration of pocks on the chorioallantoic membrane was effectively utilized for titrating RSV when: younger embryos (9 day) were employed; the eggs were incubated at 38[degree]C for 10 days in a forced draft incubator; a punch or low speed drill was used to create the false air sac and the hole was sealed immediately after injection of 0.1 ml of inoculum; the air space was returned to its normal position by placing the egg in a vertical position, thus distributing the inoculum evenly over the membrane; and the diluent for RSV was saline containing 0.001% hyaluronidase, 2% inactivated horse serum, and 100 units each of penicillin and streptomycin. This method was successfully employed with the fowl pox virus using saline or tryptose broth as diluent. However, when vaccinia virus was similarly handled large areas of confluent lesions were frequently observed even with high dilutions of virus and accurate enumeration was precluded.