1. By the use of tryptamine as substrate in the presence of tetrazolium salts in a solution buffered to pH 7.6 histochemical localization of monoamine oxidase activity is achieved during a 45 minute incubation of tissue sections at 37°C. 2. Inhibition experiments implicate the postulated acetaldehyde product of monoamine oxidase action on tryptamine and serotonin in the reduction of the tetrazoles. It was not determined whether this reduction is nonenzymatic or mediated through a flavoprotein enzyme system. 3. Localization of the formazan to autonomic ganglia and fibers, chief cells of the gastric fundus, mucosal epithelium of the duodenum and certain specific zones of the renal tubules by means of the tryptamine-tetrazolium technique was confirmed as indicating monoamine oxidase activity by identical localization using the hydrazone precipitation technique of Koelle and Valk.

The histochemistry of the "sexual segment" granules of the kidney of male diamondback rattlesnakes has been studied to define the nature of these androgenitally responsive granules. The kidneys were variously fixed and sections stained with a number of acid dyes, as well as by a variety of carbohydrate, lipid, and protein histochemical methods. The results indicate that "sexual segment" granules bind acid dyes strongly, contain some lipids and neutral glyco-or mucoproteins, much tyrosine and lysine, and some tryptophan and cysteine. A resemblance, concluded to be superficial, is noted between the histochemical properties of zymogen granules and the predominantly proteinaceous "sexual segment" granules.The existence of a macroscopically hypertrophied segment of the distal tubule of snake and lizard kidneys was first observed by Gampert in 1866. Not until early in this century, however, was the morphology and histology of this segment investigated. 'Tribondeau and Bongrand ('02), Tribondeau ('03), and Regaud and Policard ('03a,b,c) noted that in male snakes and lizards the hypertrophied, or "preterminal" segment of the renal distal tubule was greatly engorged with discrete microscopic granules. Because of this sexual dimorphism and the fact that this segment was found to enlarge seasonally in males at the same time that the testes become functional, Regaud and Policard ('03c) termed it the "sexual segment," and the granules it contains the "sexual granules." These authors' reports include complete histological details and reconstructions of nephrons of six species of snakes, and describe investigations of the effect of various fixing and staining procedures on the appearance of the nephron.Subsequent histological work (Reiss, '23; Cordier, '28; Courrier, '29; Herlant, '33; KehI, '35; Forbes, '41; Reynolds, '43; Fox, '52) on reptilian kidneys has dealt mainly with establishing species characteristics and demonstrating androgenic control of "sexual secretion." Fox ('52) in particular reviews the work on seasonal variations in the sexual segment. Although Forbes ('61) states that during the secretory phase the distal tubules contain "protein-like" granules, no histochemical or biochemical in-J. MORPH., 116 189-196. vestigations appear to have been done on this segment of the nephron of male snakes. This study reports a histochemical investigation of the nature of the sexual granules in male rattlesnake kidneys. MATERIAL AND METHODSBlocks of fresh kidneys from male diamondback rattlesnakes (Crutalus adamant e u s ) were fixed at room temperature for one day in 70% ethanol, Zenker-formol, and Lillie's ('54) aqueous mercuric formalin, and for two days in 10% aqueous buffered formalin and Bouin's fluid. The tissue was processed as usual through paraffin, and sections were cut at 6 u.A routine hematoxylin-and-eosin stain was done after all fixatives for general oversight. Since Regaud and Policard ('03c) reported a pronounced eosinophilia of the sexual granules following fixation in Zenker's fluid, staining with...

It seems improbable that leucocyte oxidase is a fatty acid peroxide, as suggested by Sehrt, on these grounds: 1. Positive reactions for aldehyde and for ethylene groups are not obtained. Hence the presence of fatty acid peroxides in leucocytes seems unlikely. 2. Peroxidase has been isolated from leucocytes by Agner. Histochemical behavior on treatment with adverse reagents and with heat indicates similarity of benzidine peroxidase and of indophenol oxidase, but dissimilarity of these from the sudanophil substance in leucocytes. 3. Sudan dyes demonstrate or produce in neutrophil leucocytes deeply colored granules of quite variable size, and the size of the granules apparently increases with the duration of staining. 4. The demonstration of sudanophil granules in leucocytes is accomplished with difficulty. The colored granules are highly stable toward many Sudan dye solvents. Decolorization is difficult and recoloration is uncertain. 5. True fats and lipoids, after staining with Sudan dyes, are readily decolorized by appropriate dye solvents and are restainable in apparently undiminished amounts. 6. Some oxidants tend to impair sudanophilia of leucocytes. Potassium bichromate improves the preservation of sudanophil lipoids, as in the Ciaccio method, but destroys the sudanophilia of polymorphonuclear leucocytes. 7. Hydrogen peroxide apparently possesses an inconstant and irregular, though sometimes quite pronounced, accelerating effect on the production of Sudan stained granules in leucocytes. 8. The sudanophilia of leucocytes depends on an as yet unexplained chemical combination of the dyes with cytoplasmic constituents which are probably not in the form of preexisting granules, rather than on lipoid staining.