Effect of host plants on the infectivity of nucleopolyhedrovirus to Spodoptera exigua larvae

Previous studies have shown that the infectivity of baculovirus to herbivores is affected by phytochemicals ingested during the acquisition of viral inoculum on the foliage of host plants. Here, we measured the effects of 14 host plant species on the infectivity of Spodoptera exigua nucleopolyhedrovirus (SeNPV) to its larvae. The order of the LD₅₀ values of SeNPV among the host plants was Ipomoea aquatica > Brassica oleracea > Raphanus sativus > Amaranthus tricolor > Spinacia oleracea > Vigna unguiculata > Solanum melongena > Capsicum annuum > Apium graveolens > Allium fistulosum > Lactuca sativa > Brassica chinensis > Zea mays > Glycine max, with 940.1 ± 2.26, 424.0 ± 0.60, 295.2 ± 1.13, 147.3 ± 0.63, 138.6 ± 0.22, 119.9 ± 0.07, 119.8 ± 0.02, 109.2 ± 0.18, 104.8 ± 0.62, 102.1 ± 0.66, 97.9 ± 0.22, 89.9 ± 0.32, 79.0 ± 0.13 and 64.0 ± 0.38 OBs per larva, respectively, and the values of mean time to death of virus‐infected larvae were 6.21 ± 0.11, 7.12 ± 0.10, 7.33 ± 0.21, 6.97 ± 0.02, 7.06 ± 0.01, 7.29 ± 0.03, 7.32 ± 0.05, 7.07 ± 0.08, 7.24 ± 0.11, 7.09 ± 0.13, 7.50 ± 0.06, 7.23 ± 0.01, 7.30 ± 0.02 and 7.19 ± 0.07 days, respectively. The mean time to death of larvae decreased with increasing viral dose, and corrected mortality decreased as the larval mean time to death increased. These findings have significance for understanding the effects of host plants on the infectivity of baculovirus to noctuids.     

Glutathione and Vitamin B12 Cooperate in Stabilization of a B12 Trafficking Chaperone Protein

The protein bCblC (bCblCpro) is a bovine homolog of a human B₁₂ trafficking chaperone that is responsible for the processing of vitamin B₁₂ and its escorted delivery in intracellular B₁₂ metabolism. In this study, we found that bCblCpro is highly thermolabile with a T _m = 42.0 ± 0.2 °C as shown for the human homolog, suggesting thermal regulation of these proteins. Binding of the reduced form of glutathione (GSH) that is a predominant cellular thiol increased the T _m of bCblCpro from 42 °C to ~45 °C (ΔT _{m max} = 3.1 ± 0.2 °C and AC₅₀ = 2.1 ± 0.5 mM). Binding of vitamin B₁₂ and its derivatives also stabilized bCblCpro increasing the T _m to a different extent and vitamin B₁₂ (cyanocobalamin, CNCbl) was the least efficient (ΔT _{m max} = 4.3 ± 0.3 °C and AC₅₀ = 291 ± 36 μM). However, the stabilizing effect of CNCbl was significantly greater for GSH-bound bCblCpro (ΔT _{m max} = 12.8 ± 0.6 °C and AC₅₀ = 9.3 ± 1.6 μM) than for GSH-free bCblCpro. In addition, the stabilizing effect of GSH was also greater for CNCbl-bound bCblCpro (ΔT _{m max} = 9.3 ± 0.3 °C and AC₅₀ = 57.0 ± 6.8 μM). Limited proteolysis revealed that thermal stabilization of bCblCpro is derived from conformational changes of the protein induced by binding of the ligands. The results in this study indicate that GSH cooperates with vitamin B₁₂ in thermal stabilization of bCblCpro and is a positive regulator of the protein.     

The accumulation of superoxide radical during the aerobic action of xanthine oxidase A requiem for H2O4−

The action of xanthine oxidase upon acetaldehyde or xanthine at pH 10.2 has been shown to be accompanied by substantial accumulation of O₂^? during the first few minutes of the reaction. H₂O₂ decreases this accumulation of O₂^? presumably because of the Haber-Weiss reaction ($\text{H}{}_2\text{O}{}_2\text{+}\text{O}{}_2{}^{\mathrm{?}}\text{→}\text{OH}{}^{\mathrm{?}}\text{+}\text{OH}\text{+}\text{O}{}_2$) and very small amounts of superoxide dismutase eliminate it. This accumulation of O₂^? was demonstrated in terms of a burst of reduction of cytochrome $\text{c}$, seen when the latter compound was added after aerobic preincubation of xanthine oxidase with its substrate. The kinetic peculiarities of the luminescence seen in the presence of luminol, which previously led to the proposal of H₂O₄^?, can now be satisfactorily explained entirely on the basis of known radical intermediates.     

The permeability of the lysosomal membrane to small ions

The permeability of the lysosomal membrane to small anions and cations was studied at 37°C and pH 7.0 in a lysosomal-mitochondrial fraction isolated from the liver of untreated rats. The extent of osmotic lysis following ion influx was used as a measure of ion permeancy. In order to preserve electroneutrality, anion influx was coupled to an influx of K⁺ in the presence of valinomycin, and cation influx was coupled to an efflux of H⁺ using the protonophore $\text{3-tert-}\text{butyl-5,2′-dichloro-4′-nitrosalicilylanilide}$. Lysosomal lysis was monitored by observing the loss of latency of two lysosomal hydrolases.The order of permeability of the lysosomal membrane to anions was found to be $\text{SCN}{}^{\mathrm{?}}\text{> I}{}^{\mathrm{?}}\text{> CH}{}_3\text{COO}{}^{\mathrm{?}}\text{> Cl}{}^{\mathrm{?}}\text{≈ HCO}{}^{\mathrm{?}}{}_3\text{≈ P}{}_{\mathrm{i}}\text{> SO}{}_4{}^{\mathrm{2?}}$ and that to cations $\text{Cs}{}^{\mathrm{+}}\text{> K}{}^{\mathrm{+}}\text{> Na}{}^{\mathrm{+}}\text{> H}{}^{\mathrm{+}}$. These orders are largely in agreement with the lyotropic series of anions and cations.The implications of these findings for the mechanism by means of which a low intralysosomal pH is produced and maintained are discussed.     

Kinetic study of dissociation of Eu(III) complex with H8dotp (H8dotp = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis(methylphosphonic acid))

The dissociation kinetics of the europium(III) complex with H₈dotp ligand was studied by means of molecular absorption spectroscopy in UV region at ionic strength 3.0 mol dm⁻³ (Na,H)ClO₄ and in temperature region 25-60 °C. Time-resolved laser-induced fluorescence spectroscopy (TRLIFS) was employed in order to determine the number of water molecules in the first coordination sphere of the europium(III) reaction intermediates and the final products. This technique was also utilized to deduce the composition of reaction intermediates in course of dissociation reaction simultaneously with calculation of rate constants and it demonstrates the elucidation of intimate reaction mechanism. The thermodynamic parameters for the formation of kinetic intermediate (ΔH⁰ = 11 ± 3 kJ mol⁻¹, ΔS⁰ = 41 ± 11 J K⁻¹ mol⁻¹) and the activation parameters (E_a = 69 ± 8 kJ mol⁻¹, ΔH^≠ = 67 ± 8 kJ mol⁻¹, ΔS^≠ = −83 ± 24 J K⁻¹ mol⁻¹) for the rate-determining step describing the complex dissociation were determined. The mechanism of proton-assisted reaction was proposed on the basis of the experimental data.     

Biooxidation of ferrous iron by immobilized Acidithiobacillus ferrooxidans in poly(vinyl alcohol) cryogel carriers

PVA-cryogels entrapping about 10⁹ cells of Acidithiobacillus ferrooxidans per ml of gel were prepared by freezing-thawing procedure, and the biooxidation of Fe²⁺ by immobilized cells was investigated in a 0.365 l packed-bed bioreactor. Fe²⁺ oxidation fits a plug-flow reaction model well. A maximum oxidation rate of 3.1 g Fe²⁺ l^–1 h^–1 was achieved at the dilution rate of 0.4 h^–1 or higher, while no obvious precipitate was determined at this time. In addition, cell-immobilized PVA-cryogels packed in bioreactor maintained their oxidative ability for more than two months under non-sterile conditions. Nomenclature: C _A0 – Concentration of Fe²⁺ in feed stream (g l^–1) C _A – Concentration of Fe^{2 +} in outlet stream (g l^{– 1}) D – Dilution rate of the packed-bed bioreactor (h^–1) F – Volumetric flow rate of iron solution (l h^–1) F _A0 – Mass flow rate of Fe²⁺ in the feed stream (g h^–1) K – Kinetic constant (l l^–1 h^–1) r _A – Oxidation rate of Fe²⁺ (g l^–1 h^–1) V – Volume of packed-bed bioreactor (l) X _A – Conversion ratio of Fe²⁺ (%)     

沙质草地3种优势植物叶片光合生理对增温和降水减少的响应北大核心CSCD

以沙质草地优势物种猪毛蒿、胡枝子和糙隐子草为研究对象,利用开顶式生长室(OTC)模拟增温,研究降水减少20%、40%和60%与增温的交互作用对3种典型植物叶片光合气体交换特征及叶绿素荧光特征的影响,以揭示沙质草地3种优势植物对气候变化的响应规律。结果显示:(1)与自然温度相比,OTC模拟增温增加了猪毛蒿C_(i),显著降低了胡枝子G_(s)、P_(n)和T_(r)、糙隐子草G_(s)和P_(n)、猪毛蒿WUE和L_(s),也显著降低了猪毛蒿和胡枝子F_(v)/F_(m)和F_(v)/F_(o)。(2)无论增温与否,随着降水减少幅度的增加,猪毛蒿G_(s)和P_(n)呈下降趋势,且中度以上的干旱胁迫下(降水减少>40%)胡枝子和糙隐子草P_(n)显著低于对照。(3)在自然温度条件下,轻度干旱胁迫时(降水减少20%)猪毛蒿T_(r)显著低于对照,重度干旱胁迫时(降水减少60%)其WUE、F_(v)/F_(m)和F_(v)/F_(o)显著低于对照;重度干旱胁迫时,胡枝子C_(i)显著高于对照,差异幅度达10.7%,L_(s)显著低于对照,轻度干旱胁迫时(降水减少20%)其F_(v)/F_(m)和F_(v)/F_(o)显著高于中度以上的干旱胁迫;中度以上的干旱胁迫下糙隐子草T_(r)和G_(s)显著低于对照,重度干旱胁迫时,其C_(i)、F_(v)/F_(m)和F_(v)/F_(o)显著低于对照,WUE和L_(s)显著高于对照。(4)增温与降水减少交互作用下,所有处理猪毛蒿C_(i)均高于对照,差异幅度分别达4.5%,6.0%和8.4%;胡枝子T_(r)均显著低于对照,差异幅度达57.8%;重度干旱胁迫时猪毛蒿L_(s)和WUE显著低于对照,糙隐子草F_(v)/F_(m)和F_(v)/F_(o)随降水减少而降低,中度以上的干旱胁迫时其值显著低于对照。(5)相关性分析表明,3个优势物种的P_(n)与F_(v)/F_(m)和F_(v)/F_(o)均呈显著正相关关系,其中猪毛蒿和糙隐子草的P_(n)—F_(v)/F_(m)和P_(n)—F_(v)/F_(o)斜率明显高于胡枝子。研究表明,气候变暖会在一定程度上加剧降水减少对沙质草地3种群落优势物种光合作用的抑制。     

Simultaneous Influx and Efflux of Nitrate during Uptake by Perennial Ryegrass

Experiments with intact plants of Lolium perenne previously grown with ¹⁴NO₃⁻ revealed significant efflux of this isotopic species when the plants were transferred to solutions of highly enriched ¹⁵NO₃⁻. The exuded ¹⁴NO₃⁻ was subsequently reabsorbed when the ambient solutions were not replaced. When they were frequently replaced, continual efflux of the ¹⁴NO₃⁻ was observed. Influx of ¹⁵NO₃⁻ was significantly greater than influx of ¹⁴NO₃⁻ from solutions of identical NO₃⁻ concentration. Transferring plants to ¹⁴NO₃⁻ solutions after a six-hour period in ¹⁵NO₃⁻ resulted in efflux of the latter. Presence of Mg²⁺, rather than Ca²⁺, in the ambient ¹⁵NO₃⁻ solution resulted in a decidedly increased rate of ¹⁴NO₃⁻ efflux and a slight but significant increase in ¹⁵NO₃⁻ influx. Accordingly, net NO₃⁻ influx was slightly depressed. A model in accordance with these observations is presented; its essential features include a passive bidirectional pathway, an active uptake mechanism, and a pathway for recycling of endogenous NO₃⁻ within unstirred layers from the passive pathway to the active uptake site.     

Preferential solvation of methylmercurated calf thymus deoxyribonucleic acid.

The changes in polymer-solvent interactions that occur when native calf thymus DNA is dialyzed against Na₂SO₄ solutions of a given ionic strength and buffer concentration but of varying concentrations in methylmercuric hydroxide have been investigated with the help of solution density measurements at 25 °C and pH 6.8–7.0. From measurements executed under equilibrium dialysis conditions at the three salt levels 5 mm, 0.05 m, and 0.5 m Na₂SO₄ (m refers to molality) and in the presence of 5 mm cacodylic acid buffer, the density increments $\text{(}\text{??}\text{?c}{}_2\text{)}{}_{\mathrm{\mu }}{}^0$ for native calf thymus DNA were determined as a function of CH₃HgOH concentration. $\text{(}\text{??}\text{?c}{}_2\text{)}{}_{\mathrm{\mu }}{}^0$ was found not to vary with organomercurial concentration, irrespective of the concentration of supporting electrolyte, until a certain CH₃HgOH concentration level has been reached, viz., , beyond which $\text{(}\text{??}\text{?c}{}_2\text{)}{}_{\mathrm{\mu }}{}^0$ increases strongly with increasing concentration of CH₃HgOH. As is shown by optical melting, $\text{(}\text{??}\text{?c}{}_2\text{)}{}_{\mathrm{\mu }}{}^0$ becomes a function of organomercurial concentration the moment DNA undergoes denaturation brought about by the complexing of CH₃HgOH with the various N-binding sites of the base residues in the DNA double helix.Polymer-solvent interactions, expressed in terms of preferential water interactions (“net hydration”) and preferential salt interactions (“salt solvation”), were derived from the $\text{(}\text{??}\text{?c}{}_2\text{)}{}_{\mathrm{\mu }}{}^0$ data in combination with data obtained on the preferential interaction of CH₃HgOH with denatured DNA and data on the partial specific volumes of all major solution components, gathered from density measurements on solutions with fixed concentrations of diffusible components. Evidence is presented which shows that denaturation in general decreases the net hydration while salt becomes preferentially associated with the polyelectrolyte. This process is further amplified by the interaction of CH₃HgOH with denatured DNA: Methylmercurated DNA alters the redistribution of diffusible components at dialysis equilibrium to such an extent that in a formal sense large amounts of water are rejected from the immediate vicinity of the polymer. The molecular implications of these findings are explored. The results are further discussed in the light of previous findings where the methylmercury-induced denaturation of DNA had been studied with the help of buoyant density measurements in a Cs₂SO₄ density gradient and by velocity-sedimentation in a variety of sulfate media.     

The covariance of relatives derived from a random mating population.

Attention is drawn to errors common in the derivation of forms for the genotypic covariance of noninbred relatives from a Hardy-Weinberg population of diploids. A synthesis of Fisher's least-squares method of partitioning the genotypic variance and Malécot's probability method of expressing kinship, yields a general form. For one locus, the form is $\text{(P}{}_{\mathrm{ss}}\text{+ P}{}_{\mathrm{sd}}\text{+ P}{}_{\mathrm{ds}}\text{+ P}{}_{\mathrm{dd}}\text{)}\text{1}\text{2}\text{σ}{}_{\mathrm{a}}{}^2\text{+ (P}{}_{\mathrm{ss}}\text{P}{}_{\mathrm{dd}}\text{+ P}{}_{\mathrm{sd}}\text{P}{}_{\mathrm{ds}}\text{) σa}{}_{\mathrm{d}}{}^2$, where σ_a² is the additive genetic variance, α_d² is the variance of dominance deviations, p_ij is the probability that parental gamete i is identical by descent to parental gamete j, i = s, d indexes the parents of one relative, and j = s, d indexes those of the other. The form provides a framework for obtaining the covariance of relatives from an equilibrium population with linkage.     

Additions to the checklist of Scoliidae,Sphecidae, Pompilidae and Vespidae of Peru,with notes on the endemic status of some species (Hymenoptera,Aculeata)

The first checklist of the Peruvian Hymenoptera listed 1169 species and subspecies of aculeate wasps, including 173 species of Pompilidae, seven of Scoliidae, 39 of Sphecidae and 403 of Vespidae. Herein are reported 32 species as new for Peru based mainly on the collection of the Natural History Museum, London. The loss of the endemic status of two species is also reported: Entypus peruvianus (Rohwer) (Pompilidae: Pepsinae) and Omicron ruficolle schunkei Giordani Soika (Vespidae: Eumeninae).     

Phospholipid exchange between bilayer membranes

The mode of interaction of aqueous dispersions of phospholipid vesicles is investigated. The vesicles (average diameter 950 Å) are prepared from total lipid extracts of Escherichia coli composed of phosphatidylethanolamine, phosphatidylglycerol and cardiolipin. One type of vesicle contains $\text{trans-}\text{Δ}{}^9\text{-octadecenoate}$, the other type $\text{trans-}\text{Δ}{}^9\text{-hexadecenoate}$ as predominant acyl chain component. The vesicles show order?disorder transitions at transition temperatures, $\text{T}{}_{\mathrm{<mtext>t</mtext>}}\text{= 42°}\text{C}$ and $\text{T}{}_{\mathrm{<mtext>t</mtext>}}\text{= 29°}\text{C}$, respectively. A mixture of these vesicles is incubated at 45° C and lipid transfer is studied as a function of time using the phase transition as an indicator. The system reveals the following properties: Lipids are transferred between the two vesicle types giving rise to a vesicle population where both lipid components are homogeneously mixed. Lipid transfer is asymmetric, i.e. $\text{trans-}\text{Δ}{}^9\text{-hexadecenoate}$-containing lipid molecules appear more rapidly in the $\text{trans-}\text{Δ}{}^9\text{-octadecenoate}$-containing vesicles than vice versa. At a given molar ratio of the two types of vesicles the rate of lipid transfer is independent of the total vesicle concentration. It is concluded that lipid exchange through the water phase by way of single molecules or micelles is the mode of communication of these negatively charged lipid vesicles.     

Pressure jump relaxation kinetics of frog skin open circuit voltage and short circuit current

The relaxation kinetics of frog skin open circuit voltage, V_oc, and short circuit current I_sc, was studied by analyzing the effects of subjecting the tissue to sudden increments of hydrostatic pressure. Both V_oc and I_sc are perturbed by the pressure jump. Changes in V_oc can be resolved into three components: a rapid decrease (phase I), a second, additional decrease with time constant 2.2 s (phase II), and finally a very slow increase found only in some preparations. The amplitudes of phases I and II are linear in the range of pressures studied (<350 atm) and have respective pressure coefficients of −1.2 · 10⁻⁴atm⁻¹ and −3.7 · 10⁻⁴atm⁻¹.Under short circuit conditions phases I and II persist. The pressure coefficients of the amplitudes of phase I and II, −4.3 · 10⁻⁴atm⁻¹ and −5.0 · 10⁻⁴atm⁻¹, respectively, are larger than those of V_oc, but the time constant of phase II, 2.2 s, is the same. The sum of the amplitudes of phases I and II is directly proportional to I_sc when it is inhibited with ouabain. It is argued that in both electrical states pressure perturbs the same transport mechanism giving rise to phases I and II of V_oc and I_sc.The magnitude of the pressure coefficients of these processes implies that they arise from chemical reactions, rather than from simple, physical solution properties. Comparison of the pressure jump kinetics with the previous spectral analysis of the electrical fluctuations of frog skin suggests a common origin for both sets of phenomena.     

Structural polypeptides and products of late genes of bacteriophage Mu: Characterization and functional aspects

This paper describes the identification and functional role of late gene products of bacteriophage Mu, including an analysis of the structural proteins of the Mu virion.In vitro reconstitution of infectious phage particles has shown that four genes (E, D, I, J) control the formation of phage heads and that a cluster of eight genes (K, L, M, N, P, Q, R, S) controls the formation of phage tails.Sodium dodecyl sulphate/polyacrylamide gel electrophoresis of Mu polypeptides synthesized in Escherichia coli minicells infected by Mu phages carrying amber mutations in various late genes has resulted in the identification of the products of gene C (15.5 × 10³M_r); H (64 × 10³M_r); F (54 × 10³M_r); G (16 × 10³M_r); L (55 × 10³M_r); N (60 × 10³M_r); P (43 × 10³M_r) and S (56 × 10³M_r). Minicells infected with λpMu hybrid phages and deletion mutants of Mu were used to identify polypeptides encoded by the V-β region of the Mu genome. These are the products of genes V, W or R (41.5 × 10³M_r, and 45 × 10³M_r); U (20.5 × 10³M_r) and of genes located in the β region (24 × 10³M_r (gpgin) and 37 × 10³M_r (possibly gpmom)).Analytical separation of the proteins of the Mu virion revealed that it consists of a major head polypeptide with a molecular weight of 33 × 10³, a second head polypeptide of 54 × 10³ (gpF) and two major tail polypeptides with molecular weights of 55 × 10³ and 12.5 × 10³ (gpL and gpY, respectively). In addition, there are five minor components of the tail (including gpN, gpS and gpU) and approximately seven minor components of the head structure of the virion (including gpH).     

The genus Scapheremaeus (Acari,Oribatida, Cymbaeremaeidae) in the oribatid mite fauna of New Zealand,with description of two new species

Two new species of oribatid mites of the genus Scapheremaeus (Oribatida, Cymbaeremaeidae), Scapheremaeus gibbus sp. n. and Scapheremaeus luxtoni sp. n., are described from New Zealand. Scapheremaeus gibbus sp. n. is morphologically most similar to Scapheremaeus humeratus Balogh & Mahunka, 1967, but differs from the latter by the number of notogastral, genital and adanal setae, morphology of bothridial setae, position of adanal lyrifissures and absence of humeral processes. Scapheremaeus luxtoni sp. n. is morphologically most similar to Scapheremaeus yamashitai Aoki, 1970, but differs from the latter by the morphology of notogastral and rostral setae, morphology of leg solenidia φ₂ and development of humeral processes. The species Scapheremaeus zephyrus Colloff, 2010 is recorded for the first time in New Zealand. An identification key to the known New Zealand species of Scapheremaeus is provided.     

Salt lakes of La Mancha (Central Spain): A hot spot for tiger beetle (Carabidae,Cicindelinae) species diversity

The tiger beetle assemblage of the wetlands of La Mancha (central Spain) comprises nine species: Calomera littoralis littoralis, Cephalota maura maura, Cephalota circumdata imperialis, Cephalota dulcinea, Cicindela campestris campestris, Cicindela maroccana, Cylindera paludosa, Lophyra flexuosa flexuosa, and Myriochila melancholica melancholica. This assemblage represents the largest concentration of tiger beetles in a single 1º latitude / longitude square in Europe. General patterns of spatial and temporal segregation among species are discussed based on observations of 1462 specimens registered during an observation period of one year, from April to August. The different species of Cicindelini appear to be distributed over space and time, with little overlapping among them. Three sets of species replace each other phenologically as the season goes on. Most of the species occupy drying or dried salt lakes and salt marshes, with sparse vegetation cover. Spatial segregation is marked in terms of substrate and vegetation use. Calomera littoralis and Myriochila melancholica have been observed mainly on wet soils; Cephalota circumdata on dry open saline flats; Cephalota dulcinea and Cylindera paludosa in granulated substrates with typical halophytic vegetation; Cephalota maura is often present in man-modified areas. Cephalota circumdata and Cephalota dulcinea are included as species of special interest in the list of protected species in Castilla–La Mancha. Conservation problems for the Cicindelini assemblage arise from agricultural activities and inadequate use of sport vehicles. Attempts at restoring the original habitat, supressing old semi-industrial structures, may affect the spatial heterogeneity of the lakes, and have an effect on Cicindelinae diversity.     

Growth inhibition of hybridoma cells by ammonium ion: correlation with effects on intracellular pH

The effect of NH₄Cl addition on intracellular pH (pH _i ) was determined by flow cytometric measurements of the fluorescence of a pH-sensitive dye. The effects of NH₄Cl on growth were determined for batch growth of cells in flasks in an incubator. The addition of NH₄Cl caused a cytoplasmic acidification. A new lower steady-state value of pH _i was attained within 20–40 min of NH₄Cl addition. A correlation was found between the effects of NH₄Cl on growth and on pH _i : whereas 3 mM NH₄Cl had little effect on growth and on pH _i , 10 mM NH₄Cl caused a substantial growth inhibition and a pH _i decrease of 0.2–0.3 units. The effects of NH₄Cl on growth and on pH _i were found to be independent of the external pH value (pH _e over the range 6.8 to 7.6, except that 10 mM NH₄Cl was more toxic at pH _e 7.6. The addition of NH₄Cl caused an increase in the average cell volume at pH _e 7.6, but had no effect on the average cell volume at pH _e 's 6.8 and 7.2. For comparison, the effects of pH _e alone on growth and on pH _i were determined. There was little difference in cell growth at pH _e 's 6.8, 7.2 and 7.6. At pH _e 6.6, there was a substantial growth inhibition. Some measurements of the effects of pH _e on pH _i were made, although the steady-state value of pH _i as a function of pH _e was not determined due to limitations in the pH _i -measuring technique. These measurements showed that pH _i remained constant from pH _e 7.6 to 6.8, but fell by 0.2 units at pH _e 6.6, in agreement with the growth results.     

ON THE VARIABILITY OF CRITICAL ILLUMINATION FOR FLICKER FUSION AND INTENSITY DISCRIMINATION

From the data of experiments with bees in which threshold response is employed as a means of recognizing visual discrimination between stripes of equal width alternately illuminated by intensities I ₁ and I ₂, it is shown that the detectable increment of intensity ΔI, where ΔI = I ₂ - I ₁, is directly proportional to σ_I2 (I ₁ being fixed). From tests of visual acuity, where I ₁ = 0 and the width of the stripes is varied, σ_I2 = kI ₂ + const.; here I ₂ = ΔI, and ΔI/I ₂ = 1. When the visual excitability of the bee is changed by dark adaptation, λI ≡ kΔI (= k'' σ_ΔI) = k'''' I + const. For the measurements of critical illumination at threshold response to flicker, σ_I2 (= σ_ΔI) = k I ₂ = k'' ΔI + const. The data for critical illumination producing threshold response to flicker in the sun-fish Lepomis show for the rods σ_I2 = K I ₂ for the cones σ_I2 = K''(I ₂ + const.). The data thus indicate that in all these experiments essentially the same visual function is being examined, and that the recognition of the production of a difference in effect by alternately illuminated stripes takes place in such a way that d (ΔI)/d (σ_I2) = const., and that ΔI is directly proportional to I (or "I ₂," depending on the nature of the experiment). It is pointed out that the curve for each of the cases considered can be gotten equally well if mean I or σ_I is plotted as a function of the independent variable involved in the experiment. Certain consequences of these and related facts are important for the treatment of the general problem of intensity discrimination.