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Articles 5881 - 5900 of 5900
Full-Text Articles in Entire DC Network
Analysis Of Time Usage In Bell System Business Offices, William (Bill) H. Williams, Hwei Chen
Analysis Of Time Usage In Bell System Business Offices, William (Bill) H. Williams, Hwei Chen
Publications and Research
No abstract provided.
Temperature Dependence Of Accommodation And Excitation In Space-Clamped Axons, Rita Guttman
Temperature Dependence Of Accommodation And Excitation In Space-Clamped Axons, Rita Guttman
Publications and Research
Accommodation and excitation in space-clamped squid axons were studied with the double sucrose gap technique, using linear current ramps, short (50 µsec) square wave pulses, and rheobasic square wave pulses as stimuli. The temperature was varied from 5° to 35°C. Experimental results showed a Q10 for accommodation which was 44% higher than that for excitation. Yet calculations on the basis of the Hodgkin-Huxley equations predict equal Q10's for excitation and accommodation. Although the Hodgkin-Huxley equations are spectacularly successful for so many nerve phenomena, the differences between calculations of accommodation and these experiments, which were designed to test the equations, show …
Effect Of Low Sodium, Tetrodotoxin, And Temperature Variation Upon Excitation, Rita Guttman
Effect Of Low Sodium, Tetrodotoxin, And Temperature Variation Upon Excitation, Rita Guttman
Publications and Research
The lowering of external sodium raised both the constant quantity threshold, Qo, and the rheobase, Io, in both real space-clamped squid axons and the theoretical axon as computed on the basis of the standard Hodgkin-Huxley equations. In both real and theoretical axons the minimum intensity for excitability for short pulses, which occurs at about 15°C, was still present when low sodium replaced seawater. Low sodium did not affect the temperature dependence of the strength-duration relationship in the range, 5° to 25°C. The excitability of tetrodotoxin-treated real axons was found to be more temperature-dependent than that of normal real axons. Also …
An Analysis Of Heterochromatin In Maize Root Tips, Marion Himes
An Analysis Of Heterochromatin In Maize Root Tips, Marion Himes
Publications and Research
The B chromosomes of maize are condensed in appearance during interphase and are relatively inert genetically; therefore they fulfill the definition of heterochromatin. This heterochromatin was studied in root meristem cells by radioautography following administration of tritiated thymidine and cytidine, and was found to behave in a characteristic way, i.e. it showed asynchronous DNA synthesis and very low, if any, RNA synthesis. A cytochemical comparison of normal maize nuclei with nuclei from isogenic maize stock containing approximately 15–20 B-chromosomes in addition to the normal complement has revealed the following: (a) the DNA and histone contents are greater in nuclei with …
Dna-Protein Binding In Interphase Chromosomes, Marion Himes
Dna-Protein Binding In Interphase Chromosomes, Marion Himes
Publications and Research
The metachromatic dye, azure B, was analyzed by microspectrophotometry when bound to DNA fibers and DNA in nuclei with condensed and dispersed chromatin. The interaction of DNA and protein was inferred from the amount of metachromasy (increased β/α-peak) of azure B that resulted after specific removal of various protein fractions. Dye bound to DNA-histone fibers and frog liver nuclei fixed by freeze-methanol substitution shows orthochromatic, blue-green staining under specific staining conditions, while metachromasy (blue or purple color) results from staining DNA fibers without histone or tissue nuclei after protein removal. The dispersed chromatin of hepatocytes was compared to the condensed …
Temperature Characteristics Of Excitation In Space-Clamped Squid Axons, Rita Guttman
Temperature Characteristics Of Excitation In Space-Clamped Squid Axons, Rita Guttman
Publications and Research
Temperature characteristics of excitability in the squid giant axon were measured for the space-clamped axon with the double sucrose gap technique. Threshold strength-duration curves were obtained for square wave current pulses from 10 µsec to 10 msec and at temperatures from 5°C to 35°C. The threshold change of potential, at which an action potential separated from a subthreshold response, averaged 17 mv at 20°C with a Q10 of 1.15. The average threshold current density at rheobase was 12 µa/cm2 at 20°C with a Q10 of 2.35 compared to 2.3 obtained previously. At short times the threshold charge was 1.5·10-8 coul/cm2. …
Dna-Dependent Rna Synthesis In Chloroplasts Of Euglena Gracilis, Vinod C. Shah, Harvard Lyman
Dna-Dependent Rna Synthesis In Chloroplasts Of Euglena Gracilis, Vinod C. Shah, Harvard Lyman
Publications and Research
No abstract provided.
Role Of The Gamete Membranes In Fertilization In Saccoglossus Kowalevskii (Enteropneusta): I. The Acrosomal Region And Its Changes In Early Stages Of Fertilization, Arthur L. Colwin, Laura Hunter Colwin
Role Of The Gamete Membranes In Fertilization In Saccoglossus Kowalevskii (Enteropneusta): I. The Acrosomal Region And Its Changes In Early Stages Of Fertilization, Arthur L. Colwin, Laura Hunter Colwin
Publications and Research
Previous electron microscope studies of sperm-egg association in the annelid Hydroides revealed novel aspects with respect to the acrosomal region. To determine whether these aspects were unique, a comparable study was made of a species belonging to a widely separated phylum, Hemichordata. Osmium tetroxide-fixed polyspermic material of the enteropneust, Saccoglossus, was used. The acrosomal region includes the membrane-bounded acrosome, with its large acrosomal granule and shallow adnuclear invagination, and the periacrosomal material which surrounds the acrosome except at the apex; here, the acrosomal membrane lies very close to the enclosing sperm plasma membrane. After reaching the egg envelope, the spermatozoon …
Role Of The Gamete Membranes In Fertilization In Saccoglossus Kowalevskii (Enteropneusta): Ii. Zygote Formation By Gamete Membrane Fusion, Laura Hunter Colwin, Arthur L. Colwin
Role Of The Gamete Membranes In Fertilization In Saccoglossus Kowalevskii (Enteropneusta): Ii. Zygote Formation By Gamete Membrane Fusion, Laura Hunter Colwin, Arthur L. Colwin
Publications and Research
An earlier paper showed that in Saccoglossus the acrosomal tubule makes contact with the egg plasma membrane. The present paper includes evidence that the sperm and egg plasma membranes fuse to establish the single continuous zygote membrane which, consequently, is a mosaic. Contrary to the general hypothesis of Tyler, pinocytosis or phagocytosis plays no role in zygote formation. Contact between the gametes is actually between two newly exposed surfaces: in the spermatozoon, the surface was formerly the interior of the acrosomal vesicle; in the egg, it was membrane previously covered by the egg envelopes. The concept that all the events …
Effect Of Temperature On The Potential And Current Thresholds Of Axon Membrane, Rita Guttman
Effect Of Temperature On The Potential And Current Thresholds Of Axon Membrane, Rita Guttman
Publications and Research
The effect of temperature on the potential and current thresholds of the squid giant axon membrane was measured with gross external electrodes. A central segment of the axon, 0.8 mm long and in sea water, was isolated by flowing low conductance, isoosmotic sucrose solution on each side; both ends were depolarized in isoosmotic KCl. Measured biphasic square wave currents at five cycles per second were applied between one end of the nerve and the membrane of the central segment. The membrane potential was recorded between the central sea water and the other depolarized end. The recorded potentials are developed only …
On Two Methods Of Unbiased Estimation With Auxiliary Variates, William (Bill) H. Williams
On Two Methods Of Unbiased Estimation With Auxiliary Variates, William (Bill) H. Williams
Publications and Research
No abstract provided.
Fine Structure Of The Spermatozoon Of Hydroides Hexagonus (Annelida), With Special Reference To The Acrosomal Region, Arthur L. Colwin, Laura Hunter Colwin
Fine Structure Of The Spermatozoon Of Hydroides Hexagonus (Annelida), With Special Reference To The Acrosomal Region, Arthur L. Colwin, Laura Hunter Colwin
Publications and Research
This paper describes in some detail the structure of the acrosomal region of the spermatozoon of Hydroides as a basis for subsequent papers which will deal with the structural changes which this region undergoes during fertilization. The material was osmium-fixed and mild centrifugation was used to aggregate the spermatozoa from collection to final embedding. The studies concern also the acrosomal regions of frozen-thawed sperm prepared by a method which previously had yielded extracts with egg membrane lytic activity. The plasma membrane closely envelops four readily recognizable regions of the spermatozoon: acrosomal, nuclear, mitochondrial, and flagellar. The acrosome consists of an …
Changes In The Spermatozoon During Fertilization In Hydroides Hexagonus (Annelida): Ii. Incorporation With The Egg, Arthur L. Colwin, Laura Hunter Colwin
Changes In The Spermatozoon During Fertilization In Hydroides Hexagonus (Annelida): Ii. Incorporation With The Egg, Arthur L. Colwin, Laura Hunter Colwin
Publications and Research
This, the last of a series of three papers, deals with the final events which lead to the incorporation of the spermatozoon with the egg. The material used consisted of moderately polyspermic eggs of Hydroides hexagonus, osmium-fixed at various times up to five minutes after insemination. The first direct contact of sperm head with egg proper is by means of the acrosomal tubules. These deeply indent the egg plasma membrane, and consequently at the apex of the sperm head the surfaces of the two gametes become interdigitated. But at first the sperm and egg plasma membranes maintain their identity and …
Changes In The Spermatozoon During Fertilization In Hydroides Hexagonus (Annelida): I. Passage Of The Acrosomal Region Through The Vitelline Membrane, Laura Hunter Colwin, Arthur L. Colwin
Changes In The Spermatozoon During Fertilization In Hydroides Hexagonus (Annelida): I. Passage Of The Acrosomal Region Through The Vitelline Membrane, Laura Hunter Colwin, Arthur L. Colwin
Publications and Research
In the previous paper the structure of the acrosomal region of the spermatozoon was described. The present paper describes the changes which this region undergoes during passage through the vitelline membrane. The material used consisted of moderately polyspermic eggs of Hydroides hexagonus, osmium-fixed usually 9 seconds after insemination. There are essentially four major changes in the acrosome during passage of the sperm head through the vitelline membrane. First, the acrosome breaks open apically by a kind of dehiscence which results in the formation of a well defined orifice. Around the lips of the orifice the edges of the plasma and …
The Fine Structure Of Haematolœchus Spermatozoan Tail, J. E. Shapiro, B. R. Hershenov, G. S. Tulloch
The Fine Structure Of Haematolœchus Spermatozoan Tail, J. E. Shapiro, B. R. Hershenov, G. S. Tulloch
Publications and Research
No abstract provided.
Egg Membrane Lytic Activity Of Sperm Extract And Its Significance In Relation To Sperm Entry In Hydroides Hexagonus (Annelida), Arthur L. Colwin, Laura Hunter Colwin
Egg Membrane Lytic Activity Of Sperm Extract And Its Significance In Relation To Sperm Entry In Hydroides Hexagonus (Annelida), Arthur L. Colwin, Laura Hunter Colwin
Publications and Research
Previous electron microscope studies indicated that the individual spermatozoön of Hydroides hexagonus forms a hole in the vitelline membrane by means of lysis. Other observations established that the hole is real, being visible in living material during sperm entry. During the present investigation sea water extracts from frozen-thawed sperm were tested for lytic effect on the membrane. In normal living eggs the membrane appears as a single thick envelope, but in electron micrographs of sections it is seen to consist of a narrow outer border layer, a wide principal or middle layer, and a narrow inner border layer. After immersion …
Formation Of Sperm Entry Holes In The Vitelline Membrane Of Hydroides Hexagonus (Annelida) And Evidence Of Their Lytic Origin, Laura Hunter Colwin, Arthur L. Colwin
Formation Of Sperm Entry Holes In The Vitelline Membrane Of Hydroides Hexagonus (Annelida) And Evidence Of Their Lytic Origin, Laura Hunter Colwin, Arthur L. Colwin
Publications and Research
Electron micrographs of inseminated eggs of Hydroides hexagonus previously had shown that in the immediate vicinity of the penetrating spermatozoön a small portion of the vitelline membrane regularly was absent, and it had been suggested that this area was a hole made by lytic activity of the individual spermatozoön during the course of its passage through the membrane. This deduction would receive support if it could be established that a sperm entry hole does form in living material. During the present study a hole repeatedly observed and photographed in the membrane of living eggs was found to arise as the …
The Effect Of Ions Upon The Response Of Smooth Muscle To Cooling, Rita Guttman, Samuel M. Ross
The Effect Of Ions Upon The Response Of Smooth Muscle To Cooling, Rita Guttman, Samuel M. Ross
Publications and Research
The slow tonic responses of the anterior byssus retractor of Mytilus edulis to rapid cooling were investigated by simultaneously recording tension and resting potential changes after soaking the muscle in banthine, a powerful neuromuscular blocking agent. The quantitative relations between the amount of cooling and the amount of associated depolarization necessary for contraction at various concentrations of potentiating potassium can be expressed in a family of curves. The plateaus of the curves for sea water and for potassium-free sea water were beneath the depolarization value necessary for contraction, so that it is clear that no amount of cooling with sea …
Electron Microscope Studies Of Early Stages Of Sperm Penetration In Hydroides Hexagonus (Annelida) And Saccoglossus Kowalevskii (Enteropneusta), Arthur L. Colwin, Laura Hunter Colwin, Delbert E. Philpott
Electron Microscope Studies Of Early Stages Of Sperm Penetration In Hydroides Hexagonus (Annelida) And Saccoglossus Kowalevskii (Enteropneusta), Arthur L. Colwin, Laura Hunter Colwin, Delbert E. Philpott
Publications and Research
1. The early events of sperm entry in Saccoglossus and Hydroides are described and examined in relation to present knowledge of the acrosome reaction and of egg membrane lysins. In Saccoglossus and several other species these events occur in two phases. First. The acrosome filament of the spermatozoön spans the egg membrane barriers, reaches the reactive egg protoplasm, and causes the egg to begin its fertilization reaction. Second. The filament and its connected sperm head move through the egg membrane barriers and enter the egg proper. The first phase is completed in a matter of seconds but the second phase …
Action Of Potassium And Narcotics On Rectification In Nerve And Muscle, Rita Guttman
Action Of Potassium And Narcotics On Rectification In Nerve And Muscle, Rita Guttman
Publications and Research
Electrical rectification was demonstrated in whole sartorius muscle and sciatic nerve of Rana pipiens and also in the single giant nerve fiber of the northern squid, Ommastrephes illecibrossus. It is probably a property of the plasma membrane. Rectification decreases reversibly under the influence of increased concentrations of the potassium ion and with chloroform, veratrine sulfate and isoamyl carbamate. No effect was found with lack of calcium, excess calcium, or barium chloride. Decrease in rectification is invariably accompanied by simultaneous decrease in resting potential. A proposed explanation of the mechanism of rectification is discussed. Rectification in a living membrane, viz. a …