INTRODUCTION In the development of the recent investigations concerning leptospira, Noguchi (1) emphasized the importance of finding some accurate method for the species identification of the many strains isolated in various parts of the world. He obtained typical strains of L. icterohaemorrhagiae from Japan, Belgium, and America; guinea pigs which had been actively immunized to the Japanese strain were found to resist inoculation with the Belgian and American strains. Similarly, the one from Belgium produced an immunity which was equally effective against all of these three strains; Noguchi therefore considered them to be identical. Thus it would appear that successful cross-immunization affords satisfactory evidence of the identity of these strains of leptospira. Obviously, the final acceptance of this single test for species identification is not advisable until an extensive amount of experience has accumulated.
Thus far, three species of pathogenic leptospira have been described, namely, L. icterohaemorrhagiae of Weil's disease, L. hebdomadis of seven day fever, and L. icteroides in yellow fever.