bluuebunny/crossref_metadata_2025_split huggingface dataset:
INCREASED PHOTOREVERSAL OF ULTRAVIOLET INJURY BY FLASHING LIGHT
Authors: Christensen E. , Giese A. C. 
Published: May 2004

1. Photoreversal of ultraviolet (UV) injury was studied in the ciliate protozoan Tetrahymena pyriformis (geleii) strain W, cultured in the absence of other living organisms. The division pattern of progeny of single animals was followed in hanging drop preparations.
2. A sublethal dose of 450 ergs/mm.2 of monochromatic UV of wave length 2654 A produces a lag before the first division followed by a period of cessation of fission after the second division. This cessation sometimes lasts as long as 6 weeks, during which time the animals become smaller and rounder and more opaque. Organisms about to resume division increase in size and transparency; after a few divisions the animals regain their normal division rate.
3. The effect of UV ranging in intensity from 5 to 15 ergs/mm.2/sec. was found to obey the reciprocity law quite well for the UV effect on the division pattern of T. pyriformis. However, the same dose at lower and at higher intensities was less effective.
4. The effect of a dose of UV delivered at high intensity (19 ergs/mm.2/sec.) could be increased by flashing the light, indicating that the system became saturated in the continuous light.
5. A photoreversing dose of monochromatic blue light of wave length 4350 A was found to be more effective when delivered as continuous light at a low intensity, or as intermittent light at a high intensity, rather than as continuous light at the high intensity—indicating that a dark mechanism participates in photoreversal.
6. The time for the dark reaction was determined to be of the order of a few hundredths of a second in experiments in which different lengths of dark period were used while maintaining a constant light period of 0.0025 second.
7. For Colpidium colpoda the efficiency of a given dose of photoreversing light was increased by flashing the light.
8. The present experiments are interpreted in terms of data available in the literature.
APPEARANCE OF NEW PHAGE TYPES AND NEW LYSOGENIC STRAINS AFTER ADAPTATION OF LYSOGENIC B. MEGATHERIUM TO AMMONIUM SULFATE CULTURE MEDIUM
Authors: Northrop John H. , Murphy James S. ,   With the Technical Assistance of Marie King
Published: May 2004

1. Lysogenic B. megatherium 899a was adapted to growth in a minimal ammonium sulfate medium (ASCM).
2. Adaptation took place slowly and the following changes in the culture occurred:
(a) The growth rate increased from 0.5 to 1.5–2.0/hr.
(b) The culture changed from diffuse to mucoid.
(c) The total phage titer, and the gelatinase concentration decreased to 1/100 or less.
(d) The types of phage produced changed from &gt;99 per cent T (wild type) to 30 to 60 per cent miscellaneous clear types. The original T phage was replaced by a different smaller t, never observed in the original 899a culture.
(e) Several new colony types also appeared, but the colony morphology was not correlated with the phage types produced. None of the colony types was stable on repeated transfer either in peptone or ASCM, but continued to disassociate into different colony types (cf. Ivánovics, 1955).
3. Control experiments showed that these changes in phage production and colony types could not be brought about by growing sensitive B. megatherium in the presence of the various new phages, in ASCM. It is therefore unlikely that the changes observed in adapted culture were due to infection of a sensitive cell with phage.
4. Continued growth of the ASCM-adapted strain in peptone resulted in increasing the total phage titer, and also the gelatinase concentration. The growth rate returned to its original value and the ability to grow rapidly in ASCM was soon lost. The phage types, however, remained the same as in the ASCM.
5. An improved cell for steady state growth is described.
THE RELATIONS BETWEEN PREPOTENTIAL, RESTING POTENTIAL, AND LATENT PERIOD IN FROG MUSCLE FIBERS
Authors: Jenerick Howard Peter 
Published: May 2004

1. Prepotentials and action potentials were recorded from amphibian striated muscle fibers. Intracellular electrodes were used for stimulating and recording. The resting potential was varied from 55 to 120 mv. by alterations of the KCl concentration of the Ringer's fluid. The magnitude of the prepotential at the initiation of the spike potential was measured and compared to the resting potential and the latent period (time between stimulus "make" and excitation). The magnitude of this prepotential varied with the resting potential.
2. A large prepotential or cathodal depolarization was required to excite a fiber with a high resting potential. If a fiber with a high resting potential fired late (long latency), the adequate prepotential was larger than if the fiber fired early. Fibers with low resting potentials had smaller adequate prepotentials. Also, the adequate prepotential was independent of the latent period, in these depolarized fibers.
3. If the concentration of Ca++ was increased tenfold, the adequate prepotential of depolarized fibers became strongly dependent upon the latency.
4. Fibers with large or normal resting potentials were prone to respond repetitively during the passage of long duration shock, whereas depolarized and Ca++-treated fibers were not.
5. The so-called critical membrane potential (which is defined as the transmembrane potential at the point of excitation) was not independent of the resting potential.
THE EFFECT OF ADENOSINETRIPHOSPHATE UPON ACTOMYOSIN SOLUTIONS, STUDIED WITH A RECORDING DUAL BEAM LIGHT-SCATTERING PHOTOMETER
Authors: Mommaerts W. F. H. M. 
Published: May 2004

A recording dual beam light-scattering photometer is described which permits kinetic studies involving changes in turbidity, and which is not, as are single photocell instruments, affected by the errors due to the attenuation of the scattered light within the turbid medium.
With this method, a renewed study has been made of the physical changes occuring in actomyosin under the influence of ATP.
RETINENE ISOMERASE
Authors: Hubbard Ruth 
Published: May 2004

Rhodopsin is formed by the condensation of opsin with a cis isomer of retinene, called neo-b. The bleaching of rhodopsin releases all-trans retinene which must be isomerized back to neo-b in order for rhodopsin to regenerate. Both retinene isomers are in equilibrium with the corresponding isomers of vitamin A, through the alcohol dehydrogenase system.
An enzyme is found in cattle retinas and frog pigment layers which catalyzes the interconversion of all-trans and neo-b retinene. We call it "retinene isomerase." It is soluble in neutral phosphate buffer, and precipitates between 20 and 35 per cent saturation with ammonium sulfate.
In the dark, the isomerase converts all-trans and neo-b retinene to an equilibrium mixture of 5 parts neo-b and 95 parts all-trans. With opsin present to trap neo-b, the isomerase catalyzes the synthesis of rhodopsin from all-trans retinene. This reaction, however, is too slow to account for dark adaptation.
Retinene is isomerized by light, but too slowly to supply the retina with neo-b. In aqueous solution the pseudoequilibrium mixture contains about 15 per cent neo-b.
When all-trans retinene is irradiated in the presence of isomerase, the rate of formation of neo-b is increased about 5 times, and the pseudoequilibrium shifted so that the mixture now contains about 32 per cent neo-b.
The isomerase is specific for all-trans and neo-b retinene. It does not act on two other cis isomers of retinene, nor on all-trans or neo-b vitamin A.
The role of the isomerase in vision appears to be as follows: in the light, as rhodopsin is bleached to opsin and all-trans retinene, the latter is in part converted to the neo-b isomer and stored in the pigment epithelium as neo-b vitamin A. During dark adaptation, the dominant process is the trapping by opsin of neo-b retinene supplied from stores of neo-b vitamin A, and the slow isomerase-catalyzed "dark" conversion of all-trans to neo-b retinene.
AN ADENOSINETRIPHOSPHATE-ACTIVATED HEMOLYTIC SYSTEM
Authors: Borek Blanche Ann , Bovarnick Max 
Published: May 2004

1. Hemolyzed rabbit cells contain a factor which lyses human erythrocytes in vitro when Mg++ and certain nucleotides are supplied to the system. Of the nucleotides tested ATP is the most active, although no net loss of ATP or of labile phosphate seems to be associated with the hemolytic process.
2. The lytic factor appears to be a sulfhydryl enzyme which attacks the membrane of the human red cell, its hemolytic activity being inhibited by human stroma.
3. The system is activated by glutathione and is inhibited by heavy metals, oxidized glutathione, cysteine, ergothionine, and a number of metabolic inhibitors. Physostigmine has no effect.
4. Partial purification of the lytic factor has been achieved by fractional centrifugation.
THE INHIBITION OF HEMOLYSIS, AS STUDIED BY THE TECHNIQUE USED FOR INVESTIGATING PROGRESSIVE REACTIONS, AND BY A TECHNIQUE USING RADIOACTIVE HEMOLYSINS
Authors: Ponder Eric , Ponder Ruth V. 
Published: May 2004

Inhibition of hemolysis by plasma has been studied in systems containing saponin, digitonin, and sodium lauryl sulfate, using the methods developed for the study of the kinetics of progressive reactions. The results are that the progressive nature of the hemolytic reaction in saponin systems becomes less when the inhibitor is added, that the addition of inhibitor to digitonin systems has no effect on the final result although the velocity of the progressive reaction is reduced, and that the effect of plasma in lauryl sulfate systems is intermediate between the effects in saponin systems and digitonin systems. A simple explanation is that the lysin is very strongly fixed, to form an internal phase, to the cell surfaces in digitonin systems, less strongly in laurate systems, and still less strongly in saponin systems.
To answer the question as to whether, in a system in which some of the lysin forms as internal phase, the addition of an inhibitor results in a redistribution of the lysin between the internal phase and the bulk phase, sodium lauryl sulfate-S35 and sodium cetyl sulfate-S35 were prepared, and their distribution between the internal phase and the bulk phase was measured before and after the addition of plasma, the lysins being added to the cells either before or after the addition of the inhibitor. The results show that there is a large uptake of these lysins at the red cell surfaces when they are added first, and that the subsequent addition of plasma greatly reduces the quantity of lysin held in the internal phase. Further, if the inhibitor is added first and the lysin subsequently, the internal lysin phase is very incompletely formed.
Serum albumin, used in place of plasma, gives essentially similar results.
THE NATURE OF THE GECKO VISUAL PIGMENT
Authors: Crescitelli Frederick 
Published: May 2004

Retinal extracts of the Australian gecko, Phyllurus milii (White), have revealed the presence of a photosensitive pigment, unusual for terrestrial animals, because of its absorption maximum at 524 mµ. This pigment has an absorption spectrum which is identical in form with that of other visual chromoproteins. It is not a porphyropsin, for bleaching revealed the presence, not of retinene2, but of retinene1 as a chromophore. Photolabile pigments with characteristics similar to those of the Phyllurus visual pigment were also detected in retinal extracts of six other species of nocturnal geckos.
The presence of this retinal chromoprotein adequately accounts for the unusual visual sensitivity curve described by Denton for the nocturnal gecko. This pigment may have special biological significance in terms of the unique phylogenetic position of geckos as living representatives of nocturnal animals which retain some of the characteristics of their diurnal ancestors. The occurrence of this retinene1 pigment, intermediate in spectral position between rhodopsin and iodopsin, is interpreted in support of the transmutation theory of Walls. The results and interpretation of this investigation point up the fact that, from a phylogenetic point of view, too great an emphasis on the duplicity theory may serve to detract attention from the evolutionary history of the retina and the essential unitarianism of the visual cells.
THE EFFECT OF CHANGES OF ENVIRONMENT ON THE ELECTRICAL AND IONIC PATTERN OF MUSCLE
Authors: Shaw F. H. , Simon Shirley E. , Johnstone B. M. , Holman Mollie E. 
Published: May 2004

The resting and action potentials of sartorius muscles of the toad, Bufo marinus, have been measured under varying conditions of external environment. At the same time, analyses for Na+ and K+ content were carried out.
There was a slight elevation of 2 mv. when the measurements were made in phosphate-Ringer instead of in bicarbonate-Ringer. The R.P. was independent of the hydrogen ion concentration between pH 6.5 and 8.5, although at these pH's there was marked alteration in the level of Na+ and K+ in the muscle.
Alteration of the external K+ level between 0 and 50 m.eq./liter has little influence on the internal K+ concentration. When the log of the external K+ concentration is plotted against the R.P. there is not a linear relationship until the external K+ is raised above 12 m.eq./liter, at which point the cell is unexcitable. Above this value a straight line with a slope of 58 mv. per ten-fold change in concentration is obtained, but the absolute values at any point are about 35 per cent higher than those which would be given by the Nernst equation.
Alteration of the external Na+ level within a range of 45 to 650 m.eq./liter resulted in marked changes in the internal Na+ content, without, however, having any effect on the ratio Na+out/Na+in. This ratio has remained at about 3 in spite of marked fluctuations in the absolute value of the internal and external Na+ levels. When the Na+ level is lowered there is a decrease in the height of the action potential although there is no alteration in the ratio Na+out/Na+in. As the Na+ level is raised the height of the action potential is not affected even in the presence of a fivefold increase in Na+ in the Ringer.
The results do not support the conclusion that the bioelectric potentials can be calculated from the ionic ratios by means of simple physical chemical hypotheses such as the Nernst or Goldman equations.
The maintenance of the normal K+ content of the cell cannot be accounted for by a Donnan mechanism. No definite evidence has been produced to explain the mechanism of a Na+ "pump." In other words, the concept of a Na+ pump requires that there shall be a physico- or organochemical mechanism which will distinguish between Na+ and K+ (or other) ions. There is evidence that Na+ can be extruded against a concentration gradient. On the other hand the cell is able to maintain a constant ratio of external to internal Na+ even when the cell has been severely damaged by very high external Na+ levels.
EVIDENCE FOR THERMAL REACTIONS FOLLOWING EXPOSURE OF DIDINIUM TO INTERMITTENT ULTRAVIOLET RADIATIONS
Authors: Giese A. C. , Shepard D. C. , Bennett J. , Farmanfarmaian A. , Brandt C. L. 
Published: May 2004

1. The nature of ultraviolet injury and its variation with the same dose given at different intensities and wave lengths have been investigated in the protozoan Didinium nasutum, using time to the fourth division as a measure of injury.
2. The injury has been found to consist of a "slowdown" of division rate, which always occurs, and a "stasis," usually at the second division after irradiation, which appears in varying degrees among more severely injured samples.
3. Injury was found to be almost independent of intensity at three wave lengths out of four studied over a wide range of intermediate and high intensities, but was found to rise sharply with lower intensity at all except the longest wave length.
4. Flashed UV of high intensity is much more effective than the same dose of continuous radiation at high intensity and shorter total time of treatment. It is also more effective than the same dose at low intensity and equal time of treatment, though only slightly so.
5. An increase of injury with rise of temperature and with increase of dark period clearly indicates that injury depends on thermochemical reactions following the absorption of UV in Didinium.
6. The most reasonable assumption is that a similar conclusion applies to other organisms as well, and that its general application may be useful in the investigation of UV effects on protoplasm.
REFLEX DEPRESSION IN RHYTHMICALLY ACTIVE MONOSYNAPTIC REFLEX PATHWAYS
Authors: Lloyd David P. C. , Wilson Victor J. 
Published: May 2004

A study has been made of the depression that occurs when a monosynaptic reflex pathway is subjected to repetitive stimulation.
Reflex depression has a dual origin. High frequency or early depression is postsynaptic in origin and results from subnormality in the motoneurons. Low frequency, late, or enduring depression is presynaptic in origin.
The conditioning volley-test volley technique and the frequency-mean monosynaptic reflex amplitude relation yield similar information concerning reflex depression. Each method has its advantages and for some purposes one or the other of the methods necessarily must be employed.
The results of a variety of experiments are consistent with the proposition that reflex depression in the monosynaptic reflex pathway originates by action in the group IA afferent fibers of muscle origin that are responsible for monosynaptic reflex transmission.
Depression is present at a frequency of 0.1 per second (6 per minute) and absent at a frequency of 0.05 per second (3 per minute). Thus it is impractical for most purposes to employ repetition rates that satisfy the requirement for designation as "single shock" stimulations.
The temporal course of enduring depression has been determined. It is identical with that for a number of other phenomena observable in monosynaptic reflex pathways, which suggests a common origin. The mechanism of low frequency or enduring depression is discussed in the light of this suggestion.
TEMPORAL SUMMATION IN RHYTHMICALLY ACTIVE MONOSYNAPTIC REFLEX PATHWAYS
Authors: Lloyd David P. C. 
Published: May 2004

Monosynaptic reflex responses elicited by repetitive stimulation in the frequency range between 60 and 100 per second yield evidence of temporal summation.
The relation between stimulus interval and mean monosynaptic reflex response in the steady state at the frequencies studied is described adequately by an exponential decaying to 1/e in 4 msec.
Since the temporal course of spatial summation is described adequately by the same exponential it is concluded that the two phenomena, temporal and spatial, are expressions of the same fundamental process intrinsic to the workings of the monosynaptic reflex pathway, to wit the synaptic potential-residual facilitation mechanism of prior descriptions.
Some discussion of implications is appended.
CHEMICAL TRANSMISSION AND ADAPTATION
Authors: Florey Ernst 
Published: May 2004

Acetylcholine and factor I appear to be transmitter substances of excitatory and inhibitory regulatory nerve fibers supplying the sensory neurons of stretch receptor organs of the crayfish.
Sudden application of a low concentration of acetylcholine causes the impulse frequency to jump to a peak value. But immediately the frequency falls again and gradually reaches a steady state which is not far above the previous frequency level. If the acetylcholine is now withdrawn there follows a silent period after which the frequency returns to its original level. The time course of these events is identical with that of adaptations to sudden increase or decrease of stretch.
Factor I in sufficiently low concentrations causes an immediate fall in impulse frequency (silent period) which is followed by a return to a value near the previous frequency level. Withdrawal of factor I is followed by excitation and again return of the frequency to the rate measured before the application of factor I. The time course of these phenomena is identical with that of adaptations to sudden decrease and increase of stretch.
It is suggested that adaptation may be a property not only of sensory neurons but of neurons in general and that even central neurons may be considered as receptor neurons inasmuch as they respond to chemically transmitted excitatory and inhibitory stimuli.
THE COURSE OF RESPIRATION DURING THE LIFE CYCLE OF CHLORELLA CELLS
Authors: Sorokin Constantine , Myers Jack 
Published: May 2004

Endogenous and glucose respiration were studied during the life history of Chlorella pyrenoidosa. A generalized picture of the course of respiration during the life cycle is suggested. At the liberation of daughter cells from the wall of the mother cell, or soon after, the respiration rate reaches its lowest level. If the daughter cells are placed in light the respiration rate rapidly increases with time, soon reaches a maximum, and then declines slowly. Two factors are important in the initial increase—the early developmental stage of the cells and the influence of light. In autotrophically developing algae the parts played by developmental processes and by light have not been separated. Direct activation of respiratory enzymes by light, in addition to the level of respiratory substrate, cannot be excluded.
The decline of respiration rate over most of the cell history seems to have no connection with light and is probably bound to the developmental processes per se. Darkening the suspension interrupts growth and induces liberation of daughter cells, with concomitant faster decrease in respiration rate. The rate of respiration of small daughter cells decreases in darkness only slowly with time. Illumination seems necessary to bring these cells back to a high level of respiratory activity.
THE EFFECT OF ULTRAVIOLET AND WHITE LIGHT ON GROWTH RATE, LYSIS, AND PHAGE PRODUCTION OF BACILLUS MEGATHERIUM
Authors: Northrop John H. ,   With the Technical Assistance of Marie King
Published: May 2004

Cultures of megatherium 899a, growing under different conditions, were exposed to ultraviolet or white light.
1. Cultures exposed to ultraviolet light and then to white light continue to grow at the normal rate. Cultures exposed to ultraviolet light and then placed in the dark grow at the normal rate for varying lengths of time, depending on conditions, and then lyse with the liberation of from 5 to 1000 phage particles per cell, depending on the culture medium.
2. Increasing the time of exposure to ultraviolet light results in an increase in the fraction of cells which lyse in the dark. The lysis time decreases at first, remains constant over a wide range of exposure, and then increases. The lysis can be prevented by visible light after short exposure, but not after long exposures.
3. The time required for lysis is independent of the cell concentration.
4. Effect of temperature. After exposure to ultraviolet the cell concentration increases about 4 times at 20°, 30°, or 35°C., but only 1.5 to 2.0 times at 40–45°. This is due to the fact that the growth rate of the culture reaches a maximum at 38° while the lysis rate increases steadily up to 45°.
5. Terramycin decreases the growth rate and lysis rate in proportion.
6. At pH 5.1, the cultures continue to grow slowly in the dark after exposure to ultraviolet light.
7. Megatherium sensitive cells infected with T phage lyse more rapidly than ultraviolet-treated 899a, and visible light does not affect the lysis time.
The results agree with the assumption that exposure to ultraviolet results in the production of a toxic (mutagenic) substance inside the bacterial cell. This substance is inactivated by white light.