METHODS Mice were used in the experiments described here because it is comparatively easy to make an extract of the whole mouse and its excreta. It is thus possible to distinguish effects caused by the destruction or formation of histamine from those due to its transference from one part of the body to another. The technique was similar to that used by Alexander (1944) in this laboratory to study the disappearnce of injected histamine. The mice were all male and white, weighing 20-30g. and fed on oats, bread and bran. They were anasethetized with ether and then plunged wholly, except for the head and neck, into hot water at 600C.(thermostatically controlled) for 10 or 30 sec. Immediately after they had been removed from the water-bath they were carefully dried with filter paper. In some experiments they were killed within 10 min.; in others they were placed in metabolism cages in a warm room and given free access to water. The faeces and urine were collected together in the first two series of experiments. In the third series only urine was collected. After different periods they were killed by a blow on the head. Each carcass was divided into three fractions, the whole skin, the entire gastro-intestinal tract (with contents), and the rest of the body, and extracted by the methods described below. The exereta were either collected in trichloroacetic acid or preserved by the addition of chloroform to the collecting vessel. Extraction of histamine. This was carried out in two distinct ways:(a) Chemical. In some experiments, histamine was extracted by the method of Barsoum & Gaddum (1935) as modified by Code (1937). Minced tissues were ground in a mortar, and extracted for 1 hr. with10% trichloroacetic acid, using 1-5 cc of acid to 1 g. tissue. Faeces and urine were treated likewise. After filtering by gravity, an aliquot of the filtrate was taken and heated with 10 cc of conc. HCI for 1-5 hr. on a boiling water-bath. The liquid was then evapo. rated to 5 cc in vacuo andthe rest of the acid and water removed by washing the flask down