changes in endotoxin associated with loss of biological potency. J. Bacteriol. 84:803-814. 1962.-The preparation of endotoxins whose gross chemical composition approached that of refined polysaccharide haptenes raised anew the question of which

Techniques of column chromatography with cellulose ion exchangers have been successfully applied to mammalian viruses and rickettsiae. Recovery of virus is excellent, and appreciable purification in terms of phosphorus and protein removal has been demonstrated. Elution characteristics of poliovirus (types 1, 2, and 3), and Coxsackie A9 virus are similar, whereas those of ECHO-13 and Colorado tick fever differ from them as well as from each other. Elution diagrams of preparations of ECHO-13 and polio 2 viruses grown on P(32)-labeled tissue cultures show a high degree of correlation between the distribution of titratable virus and the distribution of radioactivity. A single adsorption and elution of Q fever or epidemic typhus fever rickettsiae results in a striking degree of purification, as demonstrated by electron micrographs. The chromatographic behavior of the animal viruses and rickettsiae appears to depend more upon the chemical nature of the surfaces of these infectious agents than upon their size. The chromatographic procedure described may prove useful in the preparation of purified, P(32)-labeled, fully infectious animal viruses for further fundamental research. It may also prove useful for the removal of unwanted host materials in the preparation of vaccines.

The technique of measuring deoxyribonucleic acid (DNA) complimentarity described by B. J. McCarthy and E. T. Bolton (Proc. Natl. Acad. Sci. U.S. 50:156, 1963) has enabled genetic comparisons of various bacteria, viruses, mammals, and other organisms. DNA homologies existing among five species of bacteria now classified in the genus Pasteurella (Bergey's Manual, 7th edition) were studied. The species were: P. tularense