THE functional capacity of an endocrine organ such as the islets of Langerhans can be evaluated by measurement of the amounts of circulating hormones produced by its cells and by observation of the clinical and biochemical indexes affected by its hormones. Approximately 75 per cent of the cellular elements that comprise 1,000,000 or more islets of the human pancreas are beta cells, about 20 per cent are alpha cells, and the remainder are delta cells. Glucagon and insulin, the products of alpha and beta cells, respectively, are usually secreted in a fashion such that their actions on carbohydrate, lipid and . . .