Use of visual analogue scales.

G. R. V. HUGHES plates. Sixteen wells 3 mm in diameter and 1-5 mm apart are cut in a row, and a trough 3 mm wide is cut parallel to the wells 3 mm from their cathodal side. Heat inactivated sera (8 .lI) are added to the wells, and a tissue extract containing soluble antigens (150 ,ul) is placed in the trough. We use human spleen extract4 or rabbit thymus extract at a final protein concentration of 5 mg/ml.' Electrophoresis is carried out at 12 mA/slide for 1 hour in barbital buffer, after which the slides are washed in saline and stained in 0-1 % Coomassie blue. Precipitins are identified by the formation of lines of identity with reference sera in adjacent wells (Fig. 1). CIE carried out in this way permits the detection and immunological identification of precipitating antibodies by a single technique. Staining the plates enhances the appearance of weaker precipitin lines and provides a permanent record. CIE is more sensitive than Ouchterlony immunodiffusion and far more economical in the use of reference sera and antigen extract. Furthermore the need to perform enzyme digestion of the antigens is largely eliminated because of the greater separation and sharpness of precipitin lines produced by CIE. The virtue of the method is its simplicity, making it suitable for the identification of antibodies to acidic antigens in most laboratories.