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Dithizone and aldehyde-fuchsin granules are located in the same (secretory) parts of the B cells of the pancreatic islets, but the content of each varies differently following administration o f glucose and of sodium diethyldithiocarbamate and in the course of development of diabetes. Zinc and insulin, although located in the same structures of the B cells, are evidently incorporated into different systems.If the B cells of the islets of Langherhans are strained with aldehyde-fuchsin and dithizone, two types of granules are revealed. The first reflects the insulin content of the cells [4], and the second the zinc content. The problem of the identity of these two types of granules remains unsolved: data in the literature are indirect and conflicting [5,7]. To obtain direct evidence, the method of comparing several histochemical reactions in the same section through the pancreas was used~ EXPERIMENTAL Experiments were carried out on 35 rabbits, 6 rats, 9 mice, 5 cats, and 6 dogs.Diabetes was produced in the rabbits by intravenous injection of dithizone in a dose of 50 mg/kg body weight as a 1% solution in aqueous ammonia~The criterion of diabetes was persistent hyperglycemia~ detected by repeated determination of the blood sugar by the Hagedorn-Jensen method.Five rabbits received intravenous injections of a 10% aqueous solution of sodium diethyldithiocarbamate in a dose of 500 mg/kg, while another five received i0 g/kg glucose as a 40% solution (two rabbits were given a single injection, and three received 6 separate infusions of the same dose at intervals of 4 h). Healthy intact rabbits and rabbits receiving the same volume of physiological saline acted as controls.The animals were sacrificed 1 h after receiving the injection of glucose, 30 min after injection of carbamate, and 24 h and on subsequent days after injection of dithizone. The pancreas was removed, fixed by Timm's method (in 70% ethanol saturated with H2S) , and in Bouin~s fluid~ The histochemical reaction for zinc was obtained by treating sections of a pancreas stained by Timm's method by means of a 0.2% solution of dithizone in aqueous ammonia and a 0.01% acetone solution of 8-(p-toluenesulfonylamino)-quinoline [i]o Staining with aldehyde-fuchsin was carried out on sections of the pancreas fixed by both methods. The specific reaction for insulin consisted of treatment of sections from the pancreas fixed in Bouin's fluid by means of pseudoisocyanin as described by Schiebler and Schiessler [6]. For comparison of these two reactions the following combinations were used on the same section: quinoline fluorescence with dithizone, dithizone with aldehyde-fuchsin, pseudoisocyanin with aldehyde-fuchsin. A and B cells in the islets were differentiated in control adjacent sections stained with hematoxylin-phloxine [2].

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