The international pyrogen reference preparation.

In accordance with authorization given by the WHO Expert Committee on Biological Standardization in 1950, the National Institute for Medical Research, London, obtained samples of two bacterial pyrogens and arranged for an international study of their pyrogenic properties in rabbits. The results of this study showed that the dose response curves were flat and there was a large variation in response within and between colonies of rabbits.It was agreed that some reference preparation was needed. There was no evidence to indicate the most suitable type of preparation, and there was insufficient as regards either of the two which had been studied. It was therefore decided to make available a quantity of a preparation of the O somatic antigen of Shigella dysenteriae for the International Reference Preparation. Such a substance has been obtained for this purpose and the distribution and characteristics are described.