From the results of etiological study of the disease known as akiyami which prevails in the Shida district of Shizuoka province, we conclude that:
1. Akiyami is an infectious disease caused by a leptospira.
2. The leptospira causing akiyami is very difficult to differentiate morphologically from Leptospira icterohœmorrhagiœ and Leptospira hebdomadis.
3. The strains of leptospira isolated from cases of akiyami are of two types. One type, isolated from three of the sixteen cases, is highly virulent for guinea pigs and is serologically distinct from Leptospira icterohœmorrhagiœ and Leptospira hebdomadis; we have called this the A type. The type obtained from the other cases is less virulent for guinea pigs and is serologically identical with Leptospira hebdomadis; we have called this the B type.
4. The field mouse (Microtus montebelli), which harbors Leptospira hebdomadis, has also been found to harbor the A type of akiyami.