a1 Division of Insect-Borne Diseases, Medical Research Laboratory, Kenya
1. Cyclical development of Spirochaeta duttoni in lice was observed in seven experiments. In the last four, the same strain was transmitted through four successive batches.
2. The resultant infections in animals behaved exactly like S. duttoni even after the fourth transmission through the abnormal host.
(Received August 26 1946)