The recent study of Darling1 on the relapsing fever of Panama has called renewed attention to the probable existence of several distinct varieties of spirilla or spirochetes2 causing types of relapsing fever. The subdivision of these organisms into varieties depends for the greater part on differences in the results obtained after animal inoculation, and as relatively only a few organisms have been so studied up to the present time, it seems desirable to record certain observations which I have been able to make on spirilla obtained from a patient admitted to my service at the Carney Hospital. These observations are far from complete. It was impossible to secure more than three monkeys at that time in the American market, and the local supply of white rats was too small for the simultaneous inoculation each day of several animals. These facts caused the paucity of observations on the monkeys and the