comprehensive and theoretical in scope than any of the others. It 

 served as preamble to those who wrote the other papers and may well 

 serve as such also to the readers of this book. The other papers and 

 the major discussion remarks then follow in alphabetical order of their 

 authors. It was felt that the book may be most useful for reference 

 purposes and that this arrangement will make it easiest to find a given 

 paper. Finally, we have put at the end, as a kind of appendix, a syl- 

 labus on procedui'es, facts, and interpretations in phage. This was pre- 

 pared by the phage group at Caltech, and is intended as a guide to 

 the phage literature of the last years. A short paper presented at the 

 conference by W. Weidel on his recent findings on receptor spots of 

 bacteria has been inserted into the syllabus as section 17a (p. 119). 

 This syllabus has been read by most of those whose work has been 

 cited and their comments have been taken to heart in preparing the 

 revised version here printed. No general criticism was expressed in 

 any of these comments with one exception. Dr. S. S. Cohen felt that 

 the syllabus did not give proper weight to the biochemical approach, 

 to which he himself has so pre-eminently contributed, and that this 

 failure of a proper appreciation of the biochemical results had led to 

 a false appraisal of the present situation. While the authors of the 

 syllabus do not accept this criticism they would like to draw particular 

 attention to the recent review article by Dr. Cohen in the Bacterio- 

 logical Reviews, to which reference is made in the syllabus, and which 

 should be considered as a complementary report, giving particular em- 

 phasis to the biochemical approach to phage. 



We would like to ask for special indulgence from the readers of 

 this book on two scores. First, there are many who could have made 

 important contributions but were not invited simply because we wanted 

 to have an informal conference and therefore a small group. Thus, the 

 readers should not expect a comprehensive coverage of all virus prob- 

 lems in this book. Second, when the participants were asked to make 

 their preliminary written statements, they were asked to do so with 

 the specific purpose of enlightening the fellow participants, and not a 

 wider public. It was only after the manuscripts had been received and 

 distributed that the idea of revising and printing them began to be con- 

 sidered. Originally the papers contained no references to the literature, 

 and only a few were added later. The reader should keep in mind 

 that these papers are not formal review articles. They are personal 

 evaluations of the virus problems as they appeared to some of us in 

 1950. 



The conference was sponsored by the fund for virus research of 

 the California Institute of Technology. This fund was established by the 

 James G. Boswell Foundation. 



M. DELBRliCK. 



