Since the review on virus quantitation by Sharp (1965), interest has increased in developing more accurate methods to recognize and quantitate oncornaviruses. The available quantitation procedures (Sharp 1949, Williams and Backus 1949, Kellenberger and Arber 1957), including the negative staining technique introduced by Monroe and Brandt (1970), present problems of virus recognition, especially under the following conditions: 1. highly pleomorphic particles; 2. low numbers of viral particles; 3. mycoplasmal contamination and 4. large amounts of cell debris. To improve accuracy in particle counting and particle recognition, an embedding method using pointed Beem capsules was developed.
