Phyllis Evelyn Pease

Fig. 1 Sexuality in bacteria. Interrupted transfer of plasmid DNA from one bacterium to another conferring antibiotic resistance. This illustrates, at the bacterial level, the transfer of DNA which can alter the characteristics of the recipient. (SEM)

is that the idea mooted in the first book is still a valid proposition. It has become increasingly apparent in the intervening years that AIDS and some malignant diseases, including leukaemias, may fall into the same category. Evidence for this view is adduced from several fields including tissue typing and the association of certain diseases with particular tissue types; graft versus host studies, plant pathology; computer studies and techniques of gene therapy.The book is essentially written from a biological point of view and should be of interest to biologists at all levels - undergraduates, postgraduates, biology teachers in schools and universities and applied biologists such as medical practitioners, surgeons, nurses and other health workers and veterinarians. It is also addressed to members of the general public who have a serious interest in biology. The diseases in question are considered from a broad biological base, taking into account the universality of the genetic code and the similarity in the mechanisms of protein synthesis between widely different organisms. The artificial disciplinary divisions between agricultural and medical bacteriology are regarded as having impeded the progress of medical research. It is suggested that much can be learnt by cancer research workers from studies on plant cancer. The middle image on the book cover shows a plant tumour caused by the plasmid DNA, which interferes with the growth control mechanisms of host cells, carried by the bacterium Agrobacterium tumefaciens - without the plasmid the bacterium is harmless. This discovery confirmed the reality of NGE. The possibility of a similar mechanism for some human cancers is discussed.