الفهرس 
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Abstract
During the past two decades, increasing knowledge in the field 0±’ virology has emphasized the great need for systematic studies directed toward the identification and classification of viruses. For a long time, human and animal viruses usually were classified on the basis of sympto-. matology, virulence, host range, and cytotropisms. Because such characteristics are known to be extremely variable, these criteria becan unsuitable for classification.
from the taxonomic point of view, physical and chemical properties of viruses, like other microorganisms, have furnished a more solid basis for identification and classification. Andrewes et al. (1961) have emphasized the importance of stable physical and chemical properties as prime characters to be used for virus differentiation. Cooper (1961) used nucleic acid as the first criterion, ether sensitivity as the second, and immunological characters as the third in his proposed classification. Hamparian etal. (1963) based their classification of animal viruses on acid stability or lability, nucleic acid type, and sensitivity to organic solvents (ether or chloroform). Size, shape, and heat lability were used for further subgrouping. The same tests were used by Huck (1961.i-) in his recent work on the classification of viruses. Sensitivity to ether or chloroform, to pH and to heat were the main physical and chemical properties in his system o± classification. Studies of physical and chemical characteristics, therefore, are of prime importance not only for identifying an isolate, but also provide a basis for classification into the virus groups.