Hormonal Contraception

the mechanism of transformation by RNA viruses. Benyesh-Melnick and co-workers describe the presence of DNA in purified murine leukemia-sarcoma virus preparations, suggesting that, in addition to unexpectedly complex enzymatic machinery, some tumor viruses may contain more than one type of nucleic acid. Several groups analyze differences in the membranes of transformed and normal cells. Burger, for example, has shown that receptor sites for wheat germ agglutinins appear on transformed cells. Another trend of research is to obtain conditional lethal mutants of tumor viruses with the ultimate aim of defining which viral genes are responsible for cell transformation. The volume is admirable because it presents contemporary research about oncogenic transformation at the cellular and molecular levels with only a brief interval between the meeting and publication of its papers. The manuscripts are reproduced directly with a minimum of editing. A more finished product would have certainly included some collation and interpretation of the research trends. Many of the manuscripts have extensive bibliographies so the book should serve as an excellent introduction to the literature of the oncogenic viruses. What of the impact of this research to the "cancer problem"? The focus of this volume is almost entirely on the oncogenic virus per se. Very little is said of the genetic and phenotypic changes in the cell which modulate the influence of the tumor virus; the response of host to the viral-transformed cell is not mentioned.