“…In controlled trials of the prophylactic use of antibiotics the total period of disability from exacerbations has been found to be reduced but the number of exacerbations unaffected (Murdoch, Leckie, Downie, Swain, and Gould, 1959;Francis and Spicer, 1960 ;Francis, May and Spicer, 1964). This suggests that the acute exacerbations are initiated by factors unrelated to bacterial infection but may be prolonged by its secondary effects.…”