BS1 antigen was prepared from stable B. subtilis L-forms grown in LPB and harvested (2000 g, 4 C, 10 min) in a High Speed 18 Centrifuge (MSE, Crawley, UK). The pellet was resuspended in 5 ml phosphate solution (0145 mol l ÿ1 NaCl, 001 mol l
ÿ1 phosphate, pH 71; Nairn 1976) and sonicated (Soniprep 150 Ultrasonic Disintegrator; MSE) six times until the L-forms were totally disrupted