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We utilised genetic markers (ISSR's) to investigate population structuring inCrambe maritima, a coastal perennial found in isolated populations on either side of the English Channel. Despite the expectation that smaller populations would contain lower levels of genetic diversity, we found no correlation with total population size or the number of flowering plants and genetic diversity. Although populations were genetically differentiated from each other, isolation by distance was not apparent in the whole data set or within the UK samples.Despite being sampled from a wide geographic range, the majority of diversity (71%) was contained within populations, with no unique genotype, or even allele, identifying any population. When genetic distances were plotted using MDS techniques, samples from each population had a tendency to cluster, but the spread of points was wide indicating high levels of gene flow. High levels of gene flow, through the dispersal of seeds, were verified by assignment testing, which showed that 8.7% of individuals were assigned to a population other than the one they were collected from. The pattern of genetic variation can be explained by examining the direction of currents in the English Channel and Bay of Biscay. Gene flow, via seed dispersal, is possible between UK and French populations on either side of the English Channel. In contrast, French populations on the Bay of Biscay coast are effectively isolated by the direction of currents and consequently show a greater degree of genetic differentiation. [ABSTRACT FROM AUTHOR]

An International Standard for Colistin has been established and the International Unit defined as the activity contained in 0.00004878 mg of this preparation. The unit was defined on the basis of a collaborative assay in which nine laboratories from six different countries participated. The material used to prepare the international standard had been manufactured in Japan; it was shown to have a composition similar to that of material produced in Europe and to be suitable for the assay of colistin from the existing sources of manufacture.

As supplies of the International Standard for Chlortetracycline were practically exhausted, it was replaced. The potency of the second international standard was defined on the basis of an international collaborative assay comprising 157 individual assays performed in 9 laboratories in 6 countries. The mean potencies obtained in the participating laboratories, although they varied by only 7%, were heterogeneous. However, the mean potency for all the laboratories combined did not differ significantly from that of the first international standard. The International Unit for chlortetracycline was therefore defined as the activity contained in 0.001 mg of the second international standard, corresponding to a potency of 1 000 IU/mg.

The National Institute for Medical Research, London, was requested by the WHO Expert Committee on Biological Standardization to establish an International Reference Preparation of Gramicidin. This preparation was needed to standardize preparations of gramicidin containing predominantly gramicidin A, B and C, for which purpose the International Reference Preparation of Gramicidin S cannot be used. A batch of 100 g of crystalline gramicidin obtained in 1963 was distributed into ampoules in 55 mg amounts and dried in vacuo; the ampoules were then filled with dried nitrogen and sealed. The proposed international reference preparation was assayed biologically against the Master Standard of Gramicidin of the US Food and Drug Administration in 7 laboratories in 6 countries by turbidimetric methods.Significant curvature of the dose-response lines was found for most assays; no single transformation improved the linearity of assays from all laboratories. Although significant heterogeneity of potencies was obtained in 5 laboratories the mean potency ratios for all laboratories only varied over a range of 5% to 6%. The composition of the material is 7% gramicidin B, 50% gramicidin A and 25% gramicidin C; preparations of gramicidin containing appreciably higher concentrations of gramicidin B can be expected to give invalid assays against the international reference preparation.The material has been established as the International Reference Preparation of Gramicidin with a defined potency of 1000 IU/mg. The International Unit of Gramicidin is defined as the activity of 0.001 mg of the International Reference Preparation of Gramicidin.

The study of procaine benzylpenicillin in oil with aluminium monostearate (PAM) described in this paper was undertaken to devise laboratory assay methods, based on animal tests, to evaluate those properties of PAM responsible for the persistence of penicillin in the circulation, as a preferable substitute for the existing test in man. Comparative studies of a number of batches of PAM in man proved, with statistical certainty, that the duration of the blood level of penicillin which they produced varied from batch to batch. The chemical and physical properties of the batches gave inadequate characterization and were of no value in assessing material for clinical use. A blood level duration test in rabbits was developed which reflected the blood level duration properties shown in man. The test was incorporated in the Requirements for Procaine Benzylpenicillin in Oil with Aluminium Monostearate that were set up by the WHO Expert Committee on Biological Standardization to ensure the suitability of batches for clinical use. An International Reference Preparation was necessary and was established. Batches of PAM in use in the field by WHO in anti-yaws campaigns were examined by the test described and found to be satisfactory.

An International Standard for Rolitetracycline has been established and the international unit of this antibiotic defined as the activity contained in 0.001004 mg of the international standard. The definition of the international unit was based on the results of a collaborative assay in which 8 laboratories in 6 different countries participated; a total of 133 assays were performed. The assay was in terms of the Working Standard of the USA Food and Drug Administration; mean potencies for individual laboratories varied within a range of only 2% of the mean for all assays although 7 different test organisms were used in both diffusion and turbidimetric assays. Individual assays, however, provided potencies that varied within a range of 40%.

The National Institute for Medical Research, London, was requested by the WHO Expert Committee on Biological Standardization to establish a second International Standard for Oxytetracycline, since stocks of the first International Standard were depleted. A batch of 500 g of oxytetracycline dihydrate obtained in 1963 was distributed into ampoules in 125-mg amounts; the ampoules were filled with dried nitrogen and sealed. The usual procedure of exhaustively drying the material was omitted since removal of water of hydration adversely affects stability of oxytetracycline dihydrate. The proposed replacement material has been assayed biologically in terms of the first International Standard in 9 laboratories in 7 countries by means of plate-diffusion and turbidimetric assays.Significant heterogeneity of the potencies obtained by the different laboratories and within 3 laboratories was not attributable to any known differences in assay technique; the weighted mean potencies obtained by all laboratories were within a range of +/-2% of the over-all mean potency.The potency of the second International Standard is approximately 3% less than that of the first International Standard but no significant difference in composition or purity could be detected by a variety of chemical and physical analytical methods. The material has been established as the second International Standard for Oxytetracycline with a defined potency of 880 IU/mg. The International Unit of Oxytetracycline is defined as the activity of 0.0011364 mg of the second International Standard of Oxytetracycline.

The first International Reference Preparation of Viomycin was replaced by the second international reference preparation, consisting of material from the batch that provided the second Working Standard of the US Food and Drug Administration. The International Unit of viomycin was redefined as the activity contained in 0.0012285 mg of the second international reference preparation. Examination of batches of viomycin sulfate from the various sources of production showed that the second international reference preparation was suitable for their assay, whereas a sample previously proposed as the international standard of viomycin was unsatisfactory.

The international unit of colistin methane sulfonate has been defined by collaborative assay as the activity contained in 0.00007874 mg of the international reference preparation. The definition was based on results from 7 laboratories in 5 countries which carried out assays against their existing national standards. Because of the complex heterogeneity in composition of this antibiotic the international reference preparation was not designated as an international standard.

The second International Reference Preparation of Procaine Benzylpenicillin in Oil with Aluminium Monostearate was established in replacement of the first international reference preparation. The blood-level duration test (WHO Requirements for Biological Substances, No. 9), used to evaluate batches of manufactured material in relation to this reference preparation, was revised to relate to the new reference preparation. Thus a batch now passes the test if the lower confidence limit of the ratio is greater than 0.45, instead of 0.50-the value that related to the first international reference preparation. This change will ensure that material passing the test in the future will be of the same quality as in the past.