The blood sugar in normal individuals is maintained at a relatively constant level from day to day. The sugar is being continually drained from the blood stream for storage or oxidation in the tissues and is constantly being supplied to it from the liver. After taking carbohydrate food the blood in the portal vein is enriched with glucose and the liver storehouses are replenished. The blood in the systemic circulation has a greater amount of sugar for a short time after the meal than is found in the fasting condition. When insulin is given an increase both in the storage of glycogen in the liver and in the oxidation of glucose has been noted but the exact r6le played by insulin in performing these functions is still obscure. Conditions which may affect the level of the blood sugar include disturbances in the liver which may affect storage in and release of sugar from this organ and changes in the amount or quality of the internal secretion of the pancreas-insulin.There is some variation in the normal level of the blood sugar depending on the method used. Most observers consider blood sugar readings between 80 and 120 mgm. per 100 cc. of blood as normal. Some would place the normal range between 85 and 115 mgm. In this discussion any blood sugar reading below 80 mgm. is taken as evidence of hypoglycemia. In a recent review of blood sugar methods Folin and Svedberg (1) pointed out that if plasma is used for the determination of the blood sugar instead of whole blood the discrepancies noted by many observers between the amount of fermentable sugar and the amount of reducing substances in the blood will disappear.Many conditions have been reported where hypoglycemia was found either with or without symptoms and a brief review of some of these reports may be of interest.1. Fasting. Griffith (2) found levels between 28 and 54 mgm. in 9 children who were having convulsions which could be relieved temporarily by glucose ingestion. Some of these children were vomiting and some had infections but all were taking very little nourishment. He considered