Tubercle bacilli contain a lipid component which is characterized by a high degree of toxicity. This material was termed “cord factor.” 3 It was first obtained from young bacterial cultures by superficial extraction with petroleum ether (1). A number of observations reported and discussed in previous papers (2, 3) sug gest that the material extracted in this manner originates from the surface of the bacterial cell. With the method of extraction used, it could be obtained only from young cultures of “cord-forming”(4) organisms (virulent strains and BCG). Subsequent studies showed that the petroleum ether extracts are mixtures of various compounds, only one of which is toxic (5). The toxic component was separated from the other remaining fractions and obtained in concentrated form (6).

The present experiments were begun in the summer of 1950 wi (h the intention of searching for a material of comparable toxicity in preparations which were obtained in the course of a chemical investigation of various bacterial lipids at the Institut de Biologie Physico-Chimique in Paris. The extraction procedure used in the Paris laboratory is a slight modification of the scheme elaborated by RJ Anderson and his associates (7). It has been described before (8, 9) and it is sufficient at present to state that the following fractions were obtained: