It has been found that the ability of the saliva to neutralise acids can be influenced by a large variety of means. It can be increased by introducing into the mouth alcoholic liquors, acids and other irritating substances (1, 5, 8); and by either active or passive movement of the jaws (1, 4, 5, 6, 10, 13). Foods increase the acid neutralizing power of the saliva in the following order of increasing magnitude of effect: hard boiled eggs, roast chicken, black bread, boiled potato, sour red apples and citrus fruits (3, 7). Injection of insulin was found to increase the potential alkalinity of the saliva of depancreatised dogs (9). The acid neutralising power of the saliva was found to be higher in the afternoon than in the morning (11). Dieminger (2) found the alkalinity of the saliva to be highest during fasting and to fall after breakfast. At the usual time for lunch it increased strongly, and fell during the 2-3 hours following the meal. Van der Molen and Offringa (4) found that after a meal the alkalinity of the saliva was lowered, although immediately afterwards it was usually slightly increased, but returned to its original level within 2 hours of completion of the meal. Pickerill (7) found that an acid diet (fruit, vegetables and meat rendered acid with sauces) materially increased both the amount and alkalinity of the saliva. A high cereal diet was found (12) to lower the acid neutralizing power of the saliva, while a high meat, egg, vegetable and fruit diet increased it. The acid neutralizing power decreased after a lunch of sandwiches, but fell only slightly after a meal of meat, vegetables, bread, dessert and coffee (13).