Photographic recording of precipitin bands in agar gel.

The method for producing antigen-antibody precipitin bands in agar gel, due to Ouchterlony, is becoming increasingly useful in diagnostic immunology as well as in research into antibody-antigen reactions. For both these purposes a dimensionally accurate record of all bands, including faint lines, crossovers, and spurs, is necessary for correct interpretation of the plate. The dimensional accuracy is obligatory if an investigation is to be carried out on the relative molecular weights of the proteins involved (Kormgold and Van Leeuwen, 1957). The method of drying the agar plate on to a lantern slide is not one of choice, as it is both laborious and the record is liable to deteriorate (Gell, 1955; Hayward and Augustin, 1957). Freehand drawings are both inaccurate and liable to bias. Most methods of photography used until now have employed the capacity of the precipitin band to reflect the incident light, making it necessary for the camera to be slightly inclined from the perpendicular to the plate to give