These companion volumes have been edited by two of the leading personalities in British obstetrics and gynaecology. Both have made notable contributions to their subjects, and each is an outstanding teacher who has always subscribed to the dictum that teaching needs research and research needs teaching. With such a philosophy inspiring their professional work, it would follow, therefore, that any publication of theirs would be devoid of pedantry. The reader will not be disappointed and will find an original, lucid, and constructive presentation. Their aim has been to present, so far as possible, a description of obstetrics and gynaecology as practised in Britain. It may be pertinently asked in what way British practice differs from that in other countries. The editors have forestalled this question. They believe that in obstetrics the chief modern contribution from Britain has been \" the results of the study of the relation of social and economic conditions to the health of the pregnant woman and the condition of her child.\" In gynaecology it is conservatism that has been the characteristic British contribution. Sir Eardley Holland has been responsible for the general editorship of the volume on obstetrics and has been assisted by 38 contributors selected from almost all the university and teaching centres. Professor Bruce Mayes, of Sydney University, is the sole overseas contributor. Included in this obstetric oligarchy are physicians, paediatricians, anatomists, a psychiatrist, a venereologist, a medical statistician, and a barrister. The co-authors have been allocated subjects in which they are acknowledged experts; thus each chapter is authoritative and at the same time original. Mr. Aleck Bourne has enlisted the help of 21 authors for the volume on gynaecology, and among these is an anatomist, a psychiatrist, a venereologist, and a barrister. He has always emphasized the importance of the basic sciences in relation to clinical medicine ; the reader will appreciate this from the contents and their presentation. It is doubtful whether a general work of this calibre should contain even brief accounts and exiguous illustrations of operations. The excellent chapter on the cervix uteri is impaired by the descriptions (and diagrams) of the operations for amputation of the cervix and trachelorrhaphy. Those who need pictorial assistance for their surgical technique would refer to a tome on operative surgery. Both volumes are illustrated with diagrams and plates of artistic distinction, and the publishers are to be congratulated on their production. The editors have succeeded in their aim. Their task has been sisyphean, but they have produced a magnunm opus which for many years will be indispensable to those who practise obstetrics and gynaecology. W. C. W. NIXON.

https://www.bmj.com/content/bmj/1/4957/29.2.full.pdf

Identification of enterobacteriaceae

Use of magnetic techniques for the isolation of cells

The principles of magnetic separation aided by antibodies or other specific binding molecules have been used for isolation of specific viable whole organisms, antigens, or nucleic acids. Whereas growth on selective media may be helpful in isolation of a certain bacterial species, immunomagnetic separation (IMS) technology can isolate strains possessing specific and characteristic surface antigens. Further separation, cultivation, and identification of the isolate can be performed by traditional biochemical, immunologic, or molecular methods. PCR can be used for amplification and identification of genes of diagnostic importance for a target organism. The combination of IMS and PCR reduces the assay time to several hours while increasing both specificity and sensitivity. Use of streptavidin-coated magnetic beads for separation of amplified DNA fragments, containing both biotin and a signal molecule, has allowed for the conversion of the traditional PCR into an easy-to-read microtiter plate format. The bead-bound PCR amplicons can also easily be sequenced in an automated DNA sequencer. The latter technique makes it possible to obtain sequence data of 300 to 600 bases from 20 to 30 strains, starting with clinical samples, within 12 to 24 h. Sequence data can be used for both diagnostic and epidemiologic purposes. IMS has been demonstrated to be a useful method in diagnostic microbiology. Most recent publications describe IMS as a method for enhancing the specificity and sensitivity of other detection systems, such as PCR, and providing considerable savings in time compared with traditional diagnostic systems. The relevance to clinical diagnosis has, however, not yet been fully established for all of these new test principles. In the case of PCR, for example, the presence of specific DNA in a food sample does not demonstrate the presence of a live organism capable of inducing a disease. However, all tests offering increased sensitivity and specificity of detection, combined with reduced time of analysis, have to be seriously evaluated. Images

Magnetic separation techniques in diagnostic microbiology.

A model was developed to study inhibitors present in feces which prevent the use of PCR for the detection of Helicobacter pylori. A DNA fragment amplified with the same primers as H. pylori was used to spike samples before extraction by a modified QIAamp tissue method. Inhibitors, separated on an Ultrogel AcA44 column, were characterized. Inhibitors in feces are complex polysaccharides possibly originating from vegetable material in the diet.

Complex polysaccharides as PCR inhibitors in feces: Helicobacter pylori model.

This paper describes a model of the motion of superparamagnetic beads in a microfluidic channel under the influence of a weak magnetic field produced by an electric current passing through a coplanar metal wire. The model based on the conventional expression for the magnetic force experienced by a superparamagnetic bead (suspended in a biologically relevant medium) and the parameters provided by the manufacturer failed to match the experimental data. To fit the data to the model, it was necessary to modify the conventional expression for the force to account for the non-zero initial magnetization of the beads, and to use the initial magnetization and the magnetic susceptibility of the beads as adjustable parameters. The best-fit value of susceptibility deviated significantly from the value provided by the manufacturer, but was in good agreement with the value computed using the magnetization curves measured independently for the beads from the same vial as those used in the experiment. The results of this study will be useful to researchers who need an accurate prediction of the behavior of superparamagnetic beads in aqueous suspensions under the influence of weak magnetic fields. The derivation of the force on a magnetic bead due to a magnetic field also identifies the correct treatment to use for this interaction, and resolves discrepancies present throughout the literature.

The force acting on a superparamagnetic bead due to an applied magnetic field.

A combination of immunomagnetic separation (IMS) and a polymerase chain reaction (PCR) procedure was used for direct isolation and identification of Shigella dysenteriae type 1 and Shigella flexneri from feces. Immunomagnetic particles were coated with monoclonal antibody MASFB, which is specific for a common epitope of the O polysaccharides of S. dysenteriae type 1 and S. flexneri. Bacteria bound to the beads were boiled in water, and target DNA was amplified with a primer pair specific for a gene coded on the invasion-associated locus (ial) of the large virulence plasmid of all four Shigella spp. and enteroinvasive strains of Escherichia coli. A 320-bp DNA fragment was generated and detected by an alkaline phosphatase-conjugated probe. Nonviable cells were also captured and detected by this technique. The method is simple and fast (7 h) and has a detection limit of ca. 10 Shigella organisms per g in fecal samples. The combined IMS-PCR assay correctly identified all 57 samples carrying S. dysenteriae type 1 and 68 samples carrying S. flexneri from 238 fecal specimens and also permitted detection of 17 samples carrying Shigella spp. from 113 specimens from diarrheal patients in whom shigellae were not detected by conventional culture.

A A Lindberg

Papers

Detection of Shigella dysenteriae type 1 and Shigella flexneri in feces by immunomagnetic isolation and polymerase chain reaction.