2 F. M. BURNET AND W. M. STANLEY 



being their adoption of the role of strict intracellular parasite. On this view 

 we may find that any treatise on general virology will eventually be reduced 

 to a discussion of the ways by which a living cell can have its metabolic 

 activities diverted to allow the replication of material of alien pattern. As a 

 matter of fact, we have given considerable space to this general area, as 

 may be seen from an examination of the following chapter in this volume. It 

 remains necessary, however, to attempt to discuss at least representative 

 examples of each mam group of viruses. 



This leads to the second difficulty — the unevenness with which topics 

 bearing on general aspects of virology have been dealt with in the different 

 groups. Folio wmg what Sir Charles Harington (1957) has characterized as 

 "the intellectual shock that was administered" to science by the discovery 

 of crystalline tobacco mosaic virus more than 20 years ago, there occurred a 

 great surge of activity in virology. There has, for instance, been a great 

 concentration of biochemical and biophysical work on TMV (tobacco mosaic 

 virus), a moderate amount on some of the other "macromolecular" plant 

 viruses, and virtually none on the larger and less stable plant viruses. Similar 

 work on the animal viruses has lagged behind that on the plant viruses. 

 Details of the process of infection and of the interference by virus with the 

 metabolism of the host are known in much more detail about bacterial 

 viruses, particularly T2 with Escherichia coli B as host, than about any other 

 combination. Genetic work is almost limited to a few bacterial viruses and 

 influenza A virus. It is already clear that generalizations about virus be- 

 havior cannot safely be drawn on the basis of one or a few well-studied 

 examples. We have, in fact, considerable sympathy with one or two poten- 

 tial collaborators who declined the task on the basis that the time was not 

 yet ripe to undertake a general treatise on viruses. They felt that the study 

 of the bacterial viruses had perhaps gone far enough to give a reasonably 

 clear picture of the process of infection and that attempts to provide a com- 

 prehensive description of the processes involved in infection by representa- 

 tive animal, plant, and insect viruses should be deferred imtil knowledge of 

 these had reached much the same level of completeness as exists for bacterial 

 viruses. The reason for going on with the project is simply our belief that it 

 is of the very nature of science that knowledge must always be incomplete 

 and that the present is a better time to attempt our task than 5, 10, or 20 

 years ago. We believe, too, that the same two remarks will be made with 

 equal cogency at any time in the foreseeable future. 



II. The Double Approach 

 A. The Infective Particle 



Virus research is a segment of experimental biology and mevitably en- 

 counters the same methodological and interpretative difficulties that beset 



