Stomatal movement in Zea mays: Shuttle of potassium and chloride between guard cells and subsidiary cells

Summary When stomates of Zea mays open K and Cl migrate from the subsidiary cells into the guard cells; when the stomates close both elements return to the subsidiary cells. Subsidiary cells function as reservoirs for K and Cl. Import of K and Cl into the guard cells and loss of both elements from the guard cells become observable 1 or 2 min after light is turned on or off, both when histochemical methods and the electron-probe microanalyzer are used for detection. Each stomatal complex of maize contains on the average 10±3×10^-13 gram equivalents (eq) of K and 4±1×10^-13 eq of Cl. Guard cells accumulate K in the light and CO₂-free air at an average rate of 10×10^-15 eq K per minute, and Cl at approximately half that rate.     

Experiments on resting site selection by nocturnal moths

When different species of moths are presented with a choice between black and white resting backgrounds, there is a strong correlation between the colour selected and the reflectance of the forewings. Under more natural conditions, light-coloured moths usually rest on fresh vegetation whilst dark-winged species select tree bark or rest upon the ground, and different defensive strategies appear to have been adopted by species in these two latter situations. Studies on the mechanism of background selection, and on background selection in polymorphic species, are reviewed.     

DISTRIBUTION OF PEROXISOMES (MICROBODIES) IN THE NEPHRON OF THE RAT : A Cytochemical Study

The distribution of peroxisomes (microbodies) in the rat nephron was studied cytochemically, using glutaraldehyde- or formaldehyde-fixed tissue, by means of α-hydroxy acid oxidase activity in light microscopy or oxidation of 3,3'-diaminobenzidine (DAB) at pH 9 in both light and electron microscopy.The two cytochemical methods show peroxisomes to be nearly sperical particles found only in cells of the proximal convoluted tubule. Lysosomes were identified in the same or parallel sections, with β-glycerophosphate or 5'-cytidylic acid as substrate. They are found in all cells of the nephron. These cytochemical methods visualize the two organelles for light microscopy; they also permit unequivocal differentiation of all kidney peroxisomes from lysosomes in electron micrographs. Peroxisomes are larger and more reactive in the cells of the pars descendens (P₃ segment) of the proximal convolution, located in the outer medulla and medullary rays, than in the cells of the pars convoluta (P₁ and P₂ segments), situated in the cortex. In contrast, lysosomes are much smaller in the P₃ segment and larger and more reactive in the P₁ and P₂ segments. In all cells of the proximal convolution, peroxisomes tend to be concentrated nearer the base of the cells than do lysosomes. Mitochondria in P₃ cells also show low levels of DAB oxidation at pH 6, in contrast to those in P₁ and P₂ cells. The possibility is discussed that P₃ cells possess an extramitochondrial means of oxidation in which peroxisome oxidases play an important role.     

Correlation Between Degradation of Bacteriophage T2 Deoxyribonucleic Acid and the Resistance of Escherichia coli to Infection

The ability of certain strains of Escherichia coli to degrade T2 deoxyribonucleic acid to acid-soluble fragments is correlated with their high capacity to survive T2 infection.     

A Retraining Program for Inactive Physicians

During the past two years a pilot project was conducted in which 19 inactive physicians were retrained in preparation for resumption of active practice. The initial program consisted of a flexible training program of six months to one year patterned after conventional internship-residency concepts. During the second year the program was modified by providing an initial condensed indoctrination period of two months'' duration especially designed for this purpose, followed by a preceptorship type of training.The project was considered successful in permitting trainees to enter some form of active medical work, or to enroll in formal specialty training. The observations made by the faculty of the program and its accomplishments are discussed in the light of the effort expended and the cost of the project.     

A Modified Pyridine-Silver Stain for Teased Preparations of Motor and Sensory Nerve Endings in Skeletal Muscle

This technique has been developed especially to stain sensory receptors which have been localised intramuscularly by electrophysiological means. Rat intertransverse caudal muscles, removed immediately after death, are fixed for 24 hr in a freshly prepared mixture of absolute ethyl alcohol, 4.5 ml; distilled water, 5 ml; and concentrated HNO_a, 0.1 ml. After a further 24 hr in 10 ml of absolute ethyl alcohol containing 0.1 ml of ammonia solution (sp. gr. 0.88), the muscles are washed in distilled water for 30 min and placed in full strength pyridine for 2 days. They are then washed for 24 hr in distilled water (changed 5-8 times) and left in 2% AgNO₃, in the dark for 3 days at 25 C. Following reduction in 10 ml of 5% formic acid containing 0.4 gm of pyrogallol for 6-24 hr, the specimens are washed briefly in distilled water and stored in pure glycerol. The nerve endings can then be teased out and mounted in glycerol, under cover glasses ringed with a waterproof cement. The advantage of this method is that it gives consistently good staining of receptors and motor end-plates in small muscles of the rat