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 specialists to recognize the viruses under discussion, thus prompting some workers to suggest standardizing the numbering or lettering systems.

Other investigators have felt that if a classification were drawn up according to the Linnean system and that if the procedures outlined in Codes of Nomenclature were followed, a binomial nomenclature could be developed for viruses. Such a system was first presented for the plant viruses by Holmes (Handbook of Phytopathogenic Viruses, Burgess Publishing Co., Minneapolis, 1939, 221 pp). This was followed by the more complete classification given in the last edition of the Manual (6th ed., 1948, 1125).

At the 5th International Congress of Microbiology, held at Rio de Janeiro in August, 1950, the consensus of opinion seemed to be that an acceptable system of classification could be achieved by giving primary consideration to the viruses that are best known and that can be most adequately described. Specialists were asked to prepare classifications for several groups of viruses, and the results of this plan were reported in 1953 by Andrewes (Annals N. Y. Acad. Sci., 56, 1953, 428).

So-called "non-Linnean" names for a number of groups of viruses were presented in 1954 (Andrewes, Nature, 173, 1954, 620). Among these were binomial names applying to the viruses of the smallpox, herpes simplex, poliomyelitis and influenza groups as well as names applicable to some viruses causing diseases in insects.

Substantial revisions of virus taxonomy and nomenclature in the hvmian and other animal virus field have been published also in Russia by Zhdanov (OpredeliteP Virusov Cheloveka i Zhivotnych, Izd. Akad. Med. Nauk, U.S.S.R., Moskau, 1953, 348 pp) and in Canada by van Rooj-en (Canadian Jour. Microbiology, 1, 1954, 227). Revisions of the classification of viruses causing diseases in insects were published in 1949 and 1953 by Steinhaus (Bact. Rev., 13, 1949, 203; Annals N. Y. Acad. Sci., 56, 1953, 517) and in 1953 by Bergold (Annals N. Y. Acad. Sci., 56, 1953,495).

For the present it seems feasible to continue with the custom, tacitly accepted in the past, of classifying bacteriophages separately as one sub-group, viruses causing diseases in higher plants as a second sub-group and those causing diseases in man and other animals as a third sub-group. It should be recognized that this may prove to be only a temporary arrangement, necessary because we have little or no evidence to warrant taxonomic overlapping of the three groups and useful while we await critical investigations and possible development of a substitute plan capable of displaying natural relationships to better advantage. It is further possible that there may be discoveries of common physical properties which would aid in formulating an interlocking classification, for which at present we lack any substantial basis. It is interesting to note that Ryzhkov (Mikrobiologiia, 21, 1952, 458) has attempted to outline such a classification; confirmation of the ideas underlying this attempt at a unified classification must be sought in the future.

The rapid expansion of the field, by the frequent discovery of new viruses and the development of new methods for their recognition and characterization, together with some uncertainties evidenced by virologists, makes it seem inappropriate to include a formal classification of Virales in this edition of the Manual. The need for an accepted nomenclature and classification has now made itself felt, and it is expected that recognition of this will be reflected in the next report of the Committee of the I.A.M.S.