Abstract

Dilutions of a standard serum were made in saline and in negative sera, and comparative tests by immunodiffusion and by immunoosmophoresis were made against one antigenic component of Micropolyspora faeni (Thermopolyspora polyspora). The endpoint dilution of the standard serum in saline and serum in wells of different sizes was ascertained in each test. The endpoint dilution was unaffected by the distance of separation (from 1·5 mm to 6 mm) between the origins of serum and antigen, provided that the tests were read at times appropriate to each separation, the greater separations requiring longer periods of development. Higher endpoint dilutions were obtained by the use of 1% Noble agar in immunoosmophoresis than with 1% Ionagar no. 2 (Oxoid). This difference was more noticeable when low osmophoresis potentials were used.