These observations on rigor mortis were made from time to time on cats and rabbits dying after large doses of insulin, on rabbits dying as a result of prolonged thyroid feeding, and on spinal cats to which large doses of insulin had been administered to study the carbohydrate metabolism of the muscles. Rabbits which have received large doses of insulin, and which, as a result, have had periods of convulsions and collapse, may either die very quickly or may survive for long periods. The exact cause of the death is still not clear. In most cases rigor mortis sets in immediately after death, and the onset is invariably much earlier than in a normal rabbit killed by a blow on the head. The same rapid onset of rigor mortis after death from insulin has, no doubt, been noticed by other workers in rabbits and mice, and was mentioned by Baur, Kuhn and Wacker (1) as occurring in guinea-pigs. The death is always accompanied by marked hypoglycæmia.