bluuebunny/crossref_metadata_2025_split huggingface dataset:
MONOSYNAPTIC REFLEX RESPONSE OF SPINAL MOTONEURONS TO GRADED AFFERENT STIMULATION
Authors: Hunt Carlton C. 
Published: May 2004

Monosynaptic reflex response of spinal motoneurons to graded afferent volleys has been studied in natural populations and in a representative sample of individual motoneurons. By analysis of input-response relations certain of the requirements for initiation of reflex discharge have been defined.
Initation of motoneuron discharge by monosynaptic afferent excitatory volleys results from the development of transmitter potentiality among members of a pool. Transmitter potentiality is considered to have the following characteristics:
1. It is a function of the number of active excitatory synaptic knobs, the degree to which such knobs are aggregated on the motoneuron soma, and the intensity of action per knob.
2. It has an appreciable spatial decrement and rapid temporal decay.
3. While transmitter potentiality has considerable dependence on number of active excitatory knobs, proximity of such knobs is an important variable. Total activation of a discrete zone does not appear to be necessary for initiation of discharge.
In addition to initiation of discharge, volleys in monosynaptic afferent excitatory fibers facilitate response otherwise engendered. Such facilitation depends upon the production of an increment in transmitter potentiality. Facilitator potentiality has the following characteristics:
1. It depends principally on number of active excitatory synaptic knobs and intensity of action per knob.
2. Facilitatory action may result from synchronous activity in knobs interspersed among aggregations of knobs otherwise activated, thus fulfilling spatial requirements for transmitter potentiality. Alternatively a residual facilitation may result from a generalized action.
3. Residual facilitation has a slow temporal decay in comparison with transmitter potentiality.
ELECTROLYTE DISTRIBUTION AND ACTIVE SALT UPTAKE IN FROG SKIN
Authors: Huf Ernst G. , Wills Joyce P. , Arrighi Mary F. 
Published: May 2004

1. The "chloride space" in frog skin was determined and found to be 69.7 per cent by weight of wet skin. The chloride space occupies about 94 per cent of the total water space of skin. From this and other information, it appears that the "non-chloride space" measures only a part of the space occupied by the structural elements of skin. This space is referred to here as the intracellular compartment and the remainder as the extracellular compartment of frog skin. On this basis, potassium and sodium in skin are distributed as follows: total sodium, 60 to 75 µeq./gm. of wet skin; all sodium is probably extracellular; total potassium, 39 to 49 µeq./gm.; intracellular potassium, 37 to 47 µeq./gm.
2. Skins were immersed in solutions differing from each other in their sodium and potassium concentrations. Three levels of NaCl were studied: 48, 119, and 169 µeq./ml. For each of these solutions (referred to below as diluted, physiological, and concentrated saline), the potassium levels were varied from 0.1 to 20 µeq./ml. For skins in solutions low in potassium and high in sodium, it was found that an exchange of intracellular potassium against extracellular sodium occurs. The ratio for the number of potassium ions lost/number of sodium ions gained was 4:1,4:6, and 4:8 for skin in K+-free diluted, physiological, and concentrated saline, respectively.
3. Uptake of NaCl by the epithelium of frog skin is dependent on the potassium concentration of the environment. For skins in physiological saline, net uptake of NaCl was optimal (0.90 µeq. x cm.–2 x hr.–1) at 1 to 5 µeq. K+/ml. For skins in diluted and concentrated saline optimal NaCl uptake was seen at potassium concentrations of approximately 5 and 10 µeq. K+/ml., respectively. Net uptake of NaCl by the skin is also discussed, with relation to the potassium balance of skin.
4. Skin potentials decreased with increasing extracellular potassium concentration when diluted saline solutions were used. The opposite of this was found for skins in concentrated saline. For skins in physiological saline, skin potentials rose sharply from rather low values, when placed in solutions very low in potassium, to relatively high values, when immersed in solutions containing 1 to 5 µeq. K+/ml. Further increase in potassium concentration of the bath led to slight reductions in skin potentials. The highest potentials observed were of the order of 40 mv. In all cases studied, the inside was positive with relation to the outside.
5. It can be shown that values for intracellular potassium concentration as a function of extracellular potassium concentration satisfy, at a first but good approximation, Freundlich's isotherm. A modification of Freundlich's isotherm, recently introduced by Sips, may also be used to correlate the experimental data quantitatively. Since the latter isotherm has a rational interpretation, it is suggested that this be used, rather than Freundlich's isotherm, to express quantitatively the dependence of intracellular on extracellular potassium in frog skin.
RELATIONS BETWEEN PIGMENT CONTENT AND PHOTOSYNTHETIC CHARACTERISTICS IN A BLUE-GREEN ALGA
Authors: Myers Jack , Kratz W. A. 
Published: May 2004

1. The blue-green alga Anacystis nidulans was cultured under steady state conditions at 25 and 39°C. and under several different light intensities to give five different types of cells.
2. Cells were submitted to pigment analysis based upon acetone extracts and aqueous extracts obtained by sonic disintegration. The different cell types show a threefold range of chlorophyll content and a fourfold range of phycocyanin content with only minor changes in the chlorophyll/phycocyanin ratio. Cells of highest pigment content were estimated to contain 2.8 per cent chlorophyll a and 24 per cent phycocyanin, the latter on a total chromoproteid basis.
3. Light intensity curves of photosynthesis were obtained for each of the cell types at 25 and at 39°C. The slopes of the light-limited regions of the curves are approximately linear functions of chlorophyll and phycocyanin contents. Maximum light-saturated rates of photosynthesis at 25 and 39° show no simple relation to pigment content.
DELAYED LIGHT PRODUCTION BY BLUE-GREEN ALGAE, RED ALGAE, AND PURPLE BACTERIA
Authors: Arnold William , Thompson Jane 
Published: May 2004

1. Blue-green algae, red algae, and purple bacteria all show the emission of delayed light.
2. The action spectra for the production of delayed light by three species of blue-green algae have one broad band with a peak at 620 mµ.
3. The action spectrum for production of delayed light by the red algae has one peak at 550 mµ with a shoulder from 600 to 660 mµ.
4. The emission spectra of the delayed light from both the blue-green and red algae were the same as from the green algae, Chlorella.
5. The action spectra for the production of delayed light by the different species of purple bacteria tested consisted of one or more bands not resolved between 800 and 900 mµ.
6. The emission spectrum of the delayed light from the purple bacteria was largely at wave lengths longer than 900 mµ.
OSMOTIC DIURESIS AND ITS EFFECT ON TOTAL ELECTROLYTE DISTRIBUTION IN PLASMA AND URINE OF THE AGLOMERULAR TELEOST, LOPHIUS AMERICANUS
Authors: Forster Roy P. , Berglund Fredrik 
Published: May 2004

Quantitative evaluations have been made of the chief anions and cations in plasma, urine, and pericardial fluid taken both from freshly captured goosefish and from those undergoing "laboratory diuresis." Measurements included: Na, K, Ca, Mg, Cl, SO4, PO4, protein, HCO3, NH3, pH, titratable acidity, freezing point depression, creatine, trimethylamine oxide, and plasma volume. The total patterns of electrolyte distribution in these body fluids are presented.
The morphologically undifferentiated aglomerular tubule acts as a barrier to the free diffusion of monovalent electrolytes, while transporting actively the divalent ions, especially Mg.
Urine taken from freshly captured fish is hypotonic to plasma, low in electrolyte, and as much as 50 per cent of its total osmolarity is accounted for by nitrogenous components. Of these creatine is transported most actively by the renal tubule cells.
With the onset of diuresis immediately after capture, plasma osmolarity slowly rises and urine suddenly becomes isotonic with plasma as chloride floods into the urine. The active movement of Mg continues during diuresis and urine/plasma concentration ratios of 100 or more are sustained for days while the animals are kept in the laboratory. Na follows chloride and never reaches 50 per cent of plasma values, and K never appears in urine in more than mere traces.
Electrolytes in this system are viewed as not being in true equilibrium but rather as constituting a biological steady state with the distribution across renal cells being maintained against passive diffusion by the expenditure of cellular energy.
NORTHROP'S PHENOMENON
Authors: Castañeda-Agulló M. 
Published: May 2004

1. Evidence has been found that Northrop's phenomenon (so called by us) is produced in the digestion of casein or hemoglobin brought about by trypsin, papain, and pepsin either crude or crystalline in the presence of gelatin.
2. Anson's and Kunitz' methods permit the measure of proteolytic activity of any protease on casein or hemoglobin substrate in the presence of gelatin, even in very small quantities and with prolonged digestion time.
STUDIES ON THE BIOSYNTHESIS OF EXTRACELLULAR PROTEASES BY BACTERIA
Authors: Castañeda-Agulló M. 
Published: May 2004

Apparently the extracellular protease of S. marcescens is present in protein- or protein derivative-free media only when the conditions favor an abundant growth and bacterial conglomerates are formed, which possibly could be explained by assuming that the proteins of dead bacteria or proteic metabolic products act as inducers of protease formation.
Dilute solutions of gelatin induce the production of proteolytic activity after a short period of time and its rapid increase before the initial number of bacteria has been duplicated.
Calcium is necessary to preserve the activity of the enzyme formed in synthetic media but not that produced in gelatin.
MITOCHONDRIA IN THE FLIGHT MUSCLES OF INSECTS
Authors: Levenbook Leo , Williams Carroll M. 
Published: May 2004

1. In the present study a correlation has been sought between aging, flight muscle mitochrondria (sarcosomes), cytochrome c, and flight ability in the blowfly, Phormia regina.
2. During the 1st week of adult life, individual sarcosomes increase in mass from 2.7 x 10–7 µg. dry weight at the time of emergence, to 8.5 x 10–7 µg. by the 7th day. During this period of growth, the number of sarcosomes per fly (6.7 x 108) remains constant. When mature, the sarcosomes account for 32.6 per cent of the total muscle dry weight, or close to 40 per cent on a wet weight basis.
3. It appears probable that the high content of flight muscle cytochromes is entirely localized in the sarcosomes. The cytochromes continue to be synthesized and increase in titer within the sarcosomes for 7 days after adult emergence.
4. As determined spectroscopically, the various cytochrome components at all times maintain a constant ratio both to one another and to the sarcosomal dry weight. This suggests the possibility that the cytochrome system may be synthesized as a single entity.
5. The wing-beat frequency of Drosophila funebris and Phormia varies with the age of these flies, being lowest at the time of emergence and maximum after the 6th day.
6. The relations between wing-beat frequency, respiration during flight, and sarcosomal cytochrome c content are discussed. On the basis of some likely assumptions it is calculated that the cytrochrome c turnover number is over 5,000, and that the cytochrome c turns over once for every two wing-beat cycles.
THE EFFECT OF CHLORAMPHENICOL ON DEOXYRIBONUCLEIC ACID SYNTHESIS AND THE DEVELOPMENT OF RESISTANCE TO ULTRAVIOLET IRRADIATION IN E. COLI INFECTED WITH BACTERIOPHAGE T2
Authors: Tomizawa Jun-ichi , Sunakawa Sumiko 
Published: May 2004

To elucidate the role of protein synthesis in DNA formation, E. coli R2 infected with phage T2 was studied as a model, employing chloramphenicol to inhibit protein synthesis. The following results were obtained.
1. Chloramphenicol inhibited protein synthesis but not synthesis of nucleic acids in uninfected bacteria.
2. Studies of the effect of chloramphenicol on phage maturation indicated a delay of 2 minutes between time of addition and cessation of phage growth.
3. The increase of DNA in phage-infected bacteria was completely suppressed by the addition of chloramphenicol within 2 minutes following infection. Addition at later times showed progressively less inhibitory action depending upon the time interval, and addition after the 10th or 12th minute showed no appreciable effect on DNA synthesis despite the cessation of intracellular phage formation and protein synthesis.
4. When chloramphenicol was added to infected cells the increase of resistance to UV stopped within 2 minutes, whether or not DNA synthesis continued. Thus evolution of resistance paralleled the rate of DNA synthesis achieved, but not the amount of DNA accumulated.
5. We conclude that in infected bacteria, protein synthesis is necessary to initiate DNA synthesis but is not essential for its continuation. The resistance to UV that characterizes infected cells near the midpoint of the latent period is not due to accumulation of DNA, but depends on some chloramphenicol-sensitive process (probably protein synthesis) completed at about the time the rate of DNA synthesis becomes maximal.
SULFHYDRYL GROUPS AND THE STRUCTURE OF HEMOGLOBIN
Authors: Riggs Austen F. , Wolbach Robert A. 
Published: May 2004

1. Addition of 2 moles of mersalyl, mercuric chloride, p-chloromercuribenzoate (PCMB), or methyl mercury hydroxide per mole of hemoglobin greatly reduces heme-heme interactions (n), yet these substances have quite different effects on the oxygen affinity (-log p50). Mersalyl and mercuric chloride at this concentration each increase the oxygen affinity, while PCMB and methyl mercury have little or no effect on the oxygen affinity. These effects are primarily associated with the binding of —SH groups, and are largely reversed on the addition of glutathione. —SH groups do not appear to be responsible for the Bohr effect.
2. Evidence is presented for the belief that the two hemes of each half-molecule of horse hemoglobin are situated on either side of a cluster of—SH groups.
3. The mechanism of interaction between the hemes is discussed. It is concluded that the reorganization of the protein architecture which accompanies oxygenation plays a central role in this interaction, in agreement with the views of Pauling and Wyman.
THE UPTAKE OF RADIOCOLLOIDS BY MACROPHAGES IN VITRO
Authors: Gosselin Robert E. 
Published: May 2004

Macrophages isolated from the rabbit peritoneal cavity extract radioactive colloidal gold from solutions in vitro. This reaction (ultraphagocytosis) involves two phases: the reversible adsorption of gold on the cell surface and the subsequent irreversible removal of surface-bound colloid into the cell. The latter process (called ingestion) appears to proceed at a rate which is proportional at any moment to the amount of gold attached to the cell surface; the latter in turn can be related to the concentration in extracellular fluid by a simple adsorption isotherm. In terms of rate, therefore, ingestion is related to the extracellular gold concentration in the same way that many enzyme reactions are related to the substrate concentration. Although enzyme kinetics are useful in describing rates of ultraphagocytosis, there is no evidence that enzymes participate in either adsorption or ingestion or that metabolic energy is required of the macrophage. Exudative leucocytes of the heterophilic series show little or no interaction with these finely dispersed gold sols (mean particle diameter 6 to 9 millimicrons).
37°C. three parameters are sufficient to characterize the reaction between gold and a suspension of macrophages, namely an affinity constant (1/Ks), an adsorption maximum (L), and a rate constant of ingestion (k3). Although numerical values differed markedly among cells of different exudates, all three parameters were estimated in three instances. In these suspensions between 2 and 20 per cent of the surface-bound gold was ingested each minute (37°C., pH 7.4). Under conditions of surface saturation, it was estimated that tens of thousands of gold particles were attached to the surface of an average macrophage; this amount of colloid, however, occupied less than 1 per cent of the geometric area of the cell surface. Although surface saturation imposed an upper limit on the rate of ingestion, no practical limit was noted in the capacity of macrophages to continue the reaction. Optical measurements imply that within the cell agglutination of colloidal gold began promptly after its ingestion.
These data are compared with published kinetic studies on the phagocytosis of microscopic particulates and on the parasitism of bacteria by virus.
OXIDATIVE ENZYME SYSTEMS OF THE HONEY BEE, APIS MELLIFERA L
Authors: Hoskins Dale D. , Cheldelin Vernon H. , Newburgh R. W. 
Published: May 2004

1. Oxidative dissimilation has been studied in enzymes from the honey bee. Using mitochondria isolated from the thoraces, complete oxidation of most of the TCA cycle members has been shown.
2. The presence of the acetate-activating enzyme, citrate-condensing enzyme, isocitric dehydrogenase, α-ketoglutarate dehydrogenase, glucose-6-phosphate, and 6-phosphogluconic dehydrogenase has been demonstrated and the cofactor requirements established.
3. The oxidation of isocitric acid has been shown to be either non-specific for the D- or L-isomer, or the presence of a racemase is indicated.
4. The presence of the pentose cycle is indicated in the soluble portion of the thoracic homogenate.
VAGAL AND SYMPATHETIC EFFECTS ON THE PACEMAKER FIBERS IN THE SINUS VENOSUS OF THE HEART
Authors: Hutter Otto F. , Trautwein Wolfgang 
Published: May 2004

1. Action potentials from sinus venosus and auricle fibers of spontaneously beating frog hearts have been recorded with intracellular electrodes.
2. Sinus fibers show a slow depolarization, the pacemaker potential, during diastole. The amplitude of this potential varies in different parts of the sinus. In some fibers the membrane potential falls by 11 to 15 mv. during diastole and the transition to the upstroke of the action potential is comparatively gradual. In other regions the depolarization develops more slowly and the action potential takes off more abruptly from a higher membrane potential. It is proposed that the fibers showing the largest fall in membrane potential during diastole are the pacemaker fibers of the heart, and that the rest of the preparation is excited by conduction. In auricle fibers the membrane potential is constant during diastole.
3. The maximum diastolic membrane potential and the overshoot of the action potential vary inversely with the amplitude of the pacemaker potential. The highest values were measured in auricle fibers.
4. Stimulation of vagi suppresses the pacemaker potentials. While the heart is arrested the membrane potential of the sinus fibers rises to a level above the maximum diastolic value reached in previous beats. In 28 experiments vagal stimulation increased the membrane potential from an average maximal diastolic value of 55 mv. to a "resting" level of 65.4 mv. The biggest vagal polarization was 23 mv.
5. In contrast to the sinus fibers vagal inhibition does not change the diastolic membrane potential of frog auricle fibers.
6. Vagal stimulation greatly accelerates the repolarization of the action potential and reduces its amplitude. These changes were seen both in the sinus and in auricle fibers stimulated by direct shocks during vagal arrest.
7. The conduction velocity in the sinus venosus of the tortoise is reduced by vagal stimulation. Block of conduction often occurs.
8. In the frog sinus venosus sympathetic stimulation increases the rate of rise of the pacemaker potential, accelerating the beat. The threshold remains unchanged. The rate of rise of the upstroke and the amplitude of the overshoot are increased.
9. The analogies between the vagal inhibition of the heart and the nervous inhibition of other preparations are discussed.
STUDIES ON THE EFFECTS OF SUBZERO TEMPERATURES ON THE VIABILITY OF SPORES OF ASPERGILLUS FLAVUS
Authors: Mazur Peter 
Published: May 2004

1. The survival of spores of Aspergillus flavus suspended in distilled water and cooled rapidly to –70 to –75°C. was found to depend primarily on the rate of subsequent warming of the frozen suspension. Only 7 per cent of the spores germinated following slow warming at 0.9°C. per minute, whereas about 75 per cent germinated following rapid warming at 700°C. per minute.
2. Viability was dependent on the rate at which the suspensions warmed from –70 to 0°C. (subzero warming), but was not dependent on the rate of thawing of the frozen water in which the spores were suspended.
3. The logarithm of the percentage of germination appeared to be a linear function of the logarithm of the rate of subzero warming when spores were warmed at rates ranging from 0.12 to 1000°C. per minute.
4. The lethal effects of slow warming from –70 to 0°C. were more pronounced between about –20 and 0°C. than between –70 and –20°C. In the former range of temperatures, the percentage of germination decreased sharply as slow warming progressed towards 0°C.
5. Slow warming from –70 to 0°C. was more harmful to the spores than was a 1 or 2 hour exposure to constant temperatures between –70 and 0°C.
6. Slow warming was found to be more harmful than rapid warming when spores were suspended in horse serum, 0.16 molal sodium chloride, or 0.29 molal sucrose as well as in distilled water.
ACID-BASE PROPERTIES OF RHODOPSIN AND OPSIN
Authors: Radding Charles M. , Wald George 
Published: May 2004

Purified preparations of cattle rhodopsin have been titrated to various pH, irradiated, and the pH changes followed thereafter until completed. In this way we have obtained the titration curves of rhodopsin, of the immediate product of irradiation, measured within 30 seconds; and of the final product of irradiation (opsin).
The rhodopsin preparations display about 54 titratable groups per mole of pigment: about 34 base-binding and 20 acid-binding groups. In default of an absolute purification, one cannot be sure that all of these go with rhodopsin itself.
Exposure to light induces an immediate rise of pH between pH 2 and 8, maximal at about pH 5. This—followed by its slow partial or complete reversal—is the only change of pH in the physiological range (6–7). It involves the exposure of 1 new acid-binding group per mole of rhodopsin with pK about 6.6, close therefore to that of the imidazole group of histidine.
At acid and alkaline pH this immediate change is followed by slower changes, occupying up to 40 minutes at 20°C. These changes are always in the direction of neutrality. They involve increases of 5 to 6 moles acid bound at acid pH, and 7 moles base bound at alkaline pH. They are associated with the irreversible denaturation of opsin in acid and alkaline solution, as evidenced by loss of its capacity to regenerate rhodopsin. Such frank denaturation procedures as the exposure of rhodopsin to alkali or heat in the dark result in comparable acid-base changes.