this relationship is still incomplete for other serologically distinct strains of leptospires iso- lated from human and animal cases of leptospirosis. Because leptospires cannot be satisfactorily studied by the methods used for the true bacteria or even for other spirochetes, it has proved difficult to apply the species concept to this important group. The differentiation of strains of leptospires is however of epidemio- logical importance as well as of academic interest. Various schemes of differentiation have been used, but at present the most satisfactory method is based on the antigenic constitu- tion of the leptospires, which can be determined by agglutination-lysis and cross-absorption tests. Complement -fixation tests have not yet been developed as a means of typing, though they are probably of value in confirming a clinical diagnosis of leptospirosis. Neither has any system so far been evolved of cultural or biochemical tests which could be used as a basis for differentiation. Building on and extending the work begun by Schiiffner and his collaborators and con- tinued by Borg-Petersen and many other workers in this field, Wolff and Broom (Docu- menta de Medicina Geographica et Tropica, 6, 1954, 78) compared the serological characters of a number of strains of leptospires whose origins and subsequent histories could be fully authenticated. These workers assembled into 'serogroups' (serological groups) serotypes which showed marked similarities in their serological reactions. These serological groupings quite probably have some relation to the differentiation of the organisms into species, but Wolff and Broom consider that knowledge of the bionomics of leptospires is not yet suffi- ciently far advanced to allow a decision to be taken regarding the criteria on which the sub- division of the genus should ultimately be made. Hence, for the time being, they propose that the term 'serotype' should be adopted to designate the basic taxon of a serological classification based on the agglutinogens of the leptospires. In view of the tentative nature of this classification, Wolff and Broom have retained the specific epithets or place names which have been applied to various leptospires as a means of designating serotypes. In this way they follow much the same custom that has been followed by students of salmonellas. The serological Table as prepared by Wolff and Broom is given here by permission of these authors; complete bibliography will be found in their original paper.
