The mast-cell distribution in the digestive tract of the rat, dog, cat, and guinea-pig was studied. In the rat mast-cells were present in the tongue, oesophagus, and forestomach, but practically absent from the glandular stomach, duodenum, ileum, and rectum. In the other species, mast-cells were numerous throughout the whole of the digestive tract, presenting a large individual variation. In th...