The response of the caecotrophy rhythm of the rabbit to single light signals.

The direction of temporary phase shifts depends on the timing of the light signal in the dark period (1800-0600). Delays predominated following signals between 2100 and 2400, while advances tended, even more uniformly, to follow signals given between 0100 and 0400. In one animal the caecotrophy rhythm split into 2 components after a light signal at 0400, while in another it was so disturbed that the signal was followed by a coprostasis of 10 days. The phase responses to light stimuli of the rabbit caecotrophy rhythm correspond well with those obtained in nocturnal rodents.