This paper identifies sources of numerical instability within the critical loads for acidity calculation developed by Sverdrup and de Vries and examines the effects of these instabilities on critical load calculations for sitka spruce forests in Wales. It is shown that the instabilities can introduce large changes in the calculated critical load for small changes in the calculation parameters and that it is essential for researchers to be aware of such unstable parameter regions before applying the equations to experimental situations or to regional mapping.

A computer model has been developed to simulate ferromagnetic resonance (FMR) in a randomly packed interacting fine particle system. Using Stoner-Wohlfarth particles with a random distribution of easy axes, the FMR response was calculated from the second derivatives of the equilibrium energy. The results show a qualitative agreement with available experimental data and are in agreement with previous mean field calculations. However, it is shown that the mean field theory does not predict changes in the interaction effects as the field is reduced from saturation.

Caudal anaesthesia was described in 1901 but is now essentially used for paediatric surgery. From their experience of 56 caudal blocks in adult patients scheduled for pelvic surgery or endoscopy, the authors discuss the value of this technique. The anatomical and physiological basis and the main guidelines of caudal anaesthesia are recalled through some references.

Les complications neurologiques périphériques des blocs plexiques sont de survenue rare mais réelle; trois modalités physiopathologiques sont reconnues: l’atteinte mécanique par le traumatisme direct de l’aiguille et/ou l’injection intraneuronale, la neurotoxicité des solutions, l’atteinte ischémique enfin. Une sommation de ces trois mécanismes est possible. La symptomatologie de ces neuropathies est très variable, de la simple paresthésie durant quelques jours aux phénomènes hyperalgiques par lésions de désafférentation et/ou causalgie, associés à des atteintes motrices pour les formes plus sévères. Si le bilan de ces complications diffère peu d’un quelconque syndrome neurologique, il doit être cependant diligent et prudent car des incidences médico-légales sont possibles. La thérapeutique pharmacologique est proche de celle des neuropathies post-traumatiques; une exploration chirurgicale précoce est intéressante dans les formes sévères d’emblée. La prévention impose une technique rigoureuse.

An International Standard for Netilmicin has been established on the basis of a collaborative assay. There were five participating laboratories in five countries. The activity of the contents of each ampoule of the International Standard for Netilmicin is defined as 4810 IU of netilmicin.

The International Reference Preparation of Kanamycin has been replaced by the International Standard for Kanamycin. The potency of the standard is based upon a collaborative study in ten laboratories in ten countries. Each ampoule of the International Standard of Kanamycin is defined as containing the activity of 10345 International Units of Kanamycin.

The second International Standard for Nystatin has been established, the potency of which was estimated from the results of a collaborative assay carried out by nine laboratories in nine countries. Variations in the results resulted from the dissimilar compositions of the first International Standard for Nystatin and the second International Standard for Nystatin. The potency agreed upon by the collaborating laboratories was 4855 i.u. mg−1. The International Unit of Nystatin is defined as the activity contained in 0·0002059 mg of the second International Standard for Nystatin.

The antifungal polyene antibiotic candicidin isolated from soil actinomyces is produced by Streptomyces sp. It is one of many macrocyclic ring compounds which display potent antifungal properties with no apparent antibacterial activity. These antibiotics are characterized by the possession of a large macrolide ring containing a series of conjugated double bonds (1). These double bonds confer potential instability to the molecule similar to that seen with both squalene and the polyunsaturated fatty acids (PUFA) (2). This type of oxidative instability in the presence of molecular oxygen is characterized by free-radical-mediated chain reactions. Consequently, autoxidation of polyene antibiotics has been recognized as a problem of handling and storage which results in loss of antifungal activity (3).

An International Reference Preparation of Candicidin has been established, the potency of which was estimated from the results of a collaborative assay carried out by five laboratories in four countries. Variations in the results resulted from the heterogeneous nature of the antibiotic and the difficulty experienced in handling it. The potency agreed upon by the collaborating laboratories was 2098 i.u. mg−1. The International Unit of candicidin is defined as the activity contained in 0·0004766 mg of the International Reference Preparation of Candicidin.

The second International Reference Preparation of Lymecycline was established. Nine laboratories in 8 countries collaborated in assaying its potency in terms of the first International Reference Preparation, of which stocks had become exhausted. The best estimate of potency was taken to be 948 IU/mg, which was the unweighted geometric mean of a total of 124 assays. On this basis, the International Unit of lymecycline was defined as the activity contained in 0.0010548 mg of the second International Reference Preparation.