“…This paradox might be explained by differences in the sulphonamides used. Much of the available information on the serum levels obtained with procaine penicillin concerns either small doses no longer used in the treatment of gonorrhoea (Pulaski and Connell, 1949;Jones and Shooter, 1948;Boger, Crosley, Carfagno, and Bayne, 1952), or doses used for the treatment of syphilis for which lower serum levels were considered necessary (Guthe, Reynolds, Krag, and Wilcox, 1953). Data on serum levels obtained after administering various penicillin preparations are given in Tables XV to XXIV, those mainly concerned with doses relevant to the present-day treatment of gonorrhoea being presented in Tables XVII-XXIV.…”