Ringtail in infant rats is shown to depend on humidity over a wide temperature range. It is not due to infection or diet, but probably to chronic cooling by evaporation, convection and conduction.
Rats should either be bred in cages with solid floors, or else be given environmental conditions resembling those in the natural nest, which keep the young at a low saturation deficit during the early post-natal period.
I am glad to express my thanks to M. Potter, Senior Animal Technician, for his invaluable aid in keeping the records of the experimental programmes, and to G. Dimmock for his help in building and maintaining apparatus. I am also grateful to the University of London for the loan of a Cambridge portable potentiometer.