The function of the ventral velum during gill irrigation in Rana catesbeiana

1970 ◽  
Vol 48 (6) ◽  
pp. 1179-1186 ◽  
Author(s):  
Norman Gradwell
Keyword(s):  
Direct Observation ◽  
Rana Catesbeiana ◽  
Buccal Cavity ◽  
Maximum Volume ◽  
Gill Cavity ◽  
Valvular Function

The direct observation of the ventral velum in normally breathing tadpoles confirms earlier evidence for a valvular function of this structure during inspiration. The ventral velum also acts as a hydrofoil during expiration and as a mucus-secreting surface for the entrapment of suspended food particles.As the volume of water pumped per irrigation cycle is normally less than the maximum volume of the buccal cavity, it is unnecessary for the pharynx also to become filled with inspired water during the sinking of the buccal floor. Therefore the ventral velum's cyclic occlusion of the buccal cavity from the pharynx is no handicap to normal irrigation; on the contrary, it is a prerequisite for the efficiency of the pharyngeal pump.The dorsal velum does not participate in valvular activity, but deflects the respiratory current downward and inward to the gill cavity via gill clefts 2, 3, and 4. Therefore the strong flow pumped into the pharynx by buccal compression is prevented from impinging directly on the ciliated groove behind the dorsal velum and thereby interfering with the transport of food into the esophagus.

Hydrostatic pressures during normal ventilation in the bullfrog tadpole

1968 ◽  
Vol 46 (6) ◽  
pp. 1169-1174 ◽  
Author(s):  
Norman Gradwell ◽  
Valerie M. Pasztor
Keyword(s):  
Buccal Cavity ◽  
Ventilation System ◽  
Compression Stroke ◽  
Pressure Pump ◽  
Pharyngeal Pressure ◽  
Flow Through ◽  
Gill Cavity ◽  
Valvular Function ◽  
Bullfrog Tadpole ◽  
Normal Ventilation

A detailed description of the water flow through the ventilation system of the bullfrog tadpole has been facilitated by recording the time dependence of normal hydrostatic pressures in the system. The mouth and nasal intakes are discontinuous but a pharyngeal pressure pump to support the buccal pressure pump has been found to assist in maintaining a flow through the gill cavity. The alternate action of these pumps drives water into the gill cavity during almost the entire ventilation cycle and owes its efficiency to the occlusion between the buccal cavity and pharynx during the compression stroke of the pharyngeal pump. The need for a valvular function of the ventral velum has thus been demonstrated as it is the only structure between the buccal cavity and pharynx which can effect such cyclic occlusion.

The jaw and hyoidean mechanism of the bullfrog tadpole during aqueous ventilation

1968 ◽  
Vol 46 (5) ◽  
pp. 1041-1052 ◽  
Author(s):  
Norman Gradwell
Keyword(s):  
Electrical Stimulation ◽  
Direct Observation ◽  
Buccal Cavity ◽  
Time Sequence ◽  
Lower Jaw ◽  
New Interpretation ◽  
Bullfrog Tadpole

Bullfrog tadpoles (above ca. 18 C) normally achieve branchial ventilation by the rhythmic pumping of water through the buccal cavity. This is facilitated by a coordination between the mandibular and hyoidean movements. Below 70 cycle/min only the lower jaw is active, but both jaws participate at higher frequencies. The jaw and hyoidean muscles and their time sequence were investigated by direct observation, electrical stimulation, lesion, and electromyography. A consideration of jaw ligaments has led to a new interpretation of the jaw mechanism.

Gill irrigation in Rana catesbeiana. Part II. On the musculoskeletal mechanism

1972 ◽  
Vol 50 (5) ◽  
pp. 501-521 ◽  
Author(s):  
Norman Gradwell
Keyword(s):  
Ambient Temperature ◽  
Rana Catesbeiana ◽  
Irrigation System ◽  
Muscle Fibers ◽  
Gill Cavity ◽  
Initial Depression ◽  
Bullfrog Tadpole ◽  
Narrow Opening

The jaw and hyoidean movements and the activity of certain of the muscles which cause these movements have been correlated with hydrostatic pressures in the irrigation system of the bullfrog tadpole. The jaws are capable of three modes of expression: narrow opening, wide opening, and protrusion. During inspiration the initial depression of the buccal floor is passive; active depression occurs near the end of the inspiration phase.Water flows continuously from the gill cavity and is most effusive at the onset of inspiration. Intermittent variations in the amplitude of irrigation result from natural and experimental irritation of the gill cavity. These variations, or hyperirrigations, are correlated with the activity of special muscle fibers, called fibrillic fibers, in the H1c, H2a, H3a, and B4 muscles. The respective contributions to rhythmic irrigation of the alternating buccal and pharyngeal pumps depend on ambient temperature. An auxiliary branchial force pump behind the gill clefts is powered by the H3a muscle in the soft opercular skin.

Direct Observation of Heat Exchanger Deposits by Cross Sectioning

1967 ◽  
Vol 25 ◽  
pp. 364-365
Author(s):  
R. W. Anderson ◽  
D. L. Senecal
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Heat Exchanger ◽  
Direct Observation ◽  
Cross Sections ◽  
Preparation Method ◽  
Specimen Preparation ◽  
Flowing Water ◽  
Transmission Electron ◽  
Deposit Layer

A problem was presented to observe the packing densities of deposits of sub-micron corrosion product particles. The deposits were 5-100 mils thick and had formed on the inside surfaces of 3/8 inch diameter Zircaloy-2 heat exchanger tubes. The particles were iron oxides deposited from flowing water and consequently were only weakly bonded. Particular care was required during handling to preserve the original formations of the deposits. The specimen preparation method described below allowed direct observation of cross sections of the deposit layers by transmission electron microscopy.The specimens were short sections of the tubes (about 3 inches long) that were carefully cut from the systems. The insides of the tube sections were first coated with a thin layer of a fluid epoxy resin by dipping. This coating served to impregnate the deposit layer as well as to protect the layer if subsequent handling were required.

Application of a Simple Cold Stub to the Direct Observation of Frozen Hydrated Sand

1973 ◽  
Vol 31 ◽  
pp. 212-213
Author(s):  
John M. Wehrung ◽  
Richard J. Harniman
Keyword(s):  
United States ◽  
Surface Water ◽  
Direct Observation ◽  
Controlled Study ◽  
Clay Particles ◽  
Organic Debris ◽  
Rock Formations ◽  
Water Tables ◽  
Permeable Rock ◽  
Natural Means

Water tables in aquifer regions of the southwest United States are dropping off at a rate which is greater than can be replaced by natural means. It is estimated that by 1985 wells will run dry in this region unless adequate artificial recharging can be accomplished. Recharging with surface water is limited by the plugging of permeable rock formations underground by clay particles and organic debris.A controlled study was initiated in which sand grains were used as the rock formation and water with known clay concentrations as the recharge media. The plugging mechanism was investigated by direct observation in the SEM of frozen hydrated sand samples from selected depths.

Direct Observation of the Diffusionless β → β + ω Transformation in Titanium Alloys

1971 ◽  
Vol 29 ◽  
pp. 122-123
Author(s):  
N. E. Paton ◽  
D. de Fontaine ◽  
J. C. Williams
Keyword(s):  
Electron Microscope ◽  
Titanium Alloys ◽  
Direct Observation ◽  
Dark Field ◽  
X Ray Diffraction ◽  
Resistivity Measurements ◽  
Selected Area Electron Diffraction ◽  
Ti Alloys ◽  
Thin Foils ◽  
Field Device

The electron microscope has been used to study the diffusionless β → β + ω transformation occurring in certain titanium alloys at low temperatures. Evidence for such a transformation was obtained by Cometto et al by means of x-ray diffraction and resistivity measurements on a Ti-Nb alloy. The present work shows that this type of transformation can occur in several Ti alloys of suitable composition, and some of the details of the transformation are elucidated by means of direct observation in the electron microscope.Thin foils were examined in a Philips EM-300 electron microscope equipped with a uniaxial tilt, liquid nitrogen cooled, cold stage and a high resolution dark field device. Selected area electron diffraction was used to identify the phases present and the ω-phase was imaged in dark field by using a (101)ω reflection. Alloys were water quenched from 950°C, thinned, and mounted between copper grids to minimize temperature gradients in the foil.

A New 1000kv Electron Microscope

1969 ◽  
Vol 27 ◽  
pp. 100-101
Author(s):  
J.L. Williams ◽  
K. Heathcote ◽  
E.J. Greer
Keyword(s):  
Electron Microscope ◽  
Direct Observation ◽  
High Voltage ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Specimen Thickness ◽  
Voltage Electron ◽  
High Voltage Electron Microscope ◽  
Dynamic Experiments ◽  
Conventional Instrument

High Voltage Electron Microscope already offers exciting experimental possibilities to Biologists and Materials Scientists because the increased specimen thickness allows direct observation of three dimensional structure and dynamic experiments on effectively bulk specimens. This microscope is designed to give maximum accessibility and space in the specimen region for the special stages which are required. At the same time it provides an ease of operation similar to a conventional instrument.

Ultrastructural Features of the Oral Apparatus of Stentor

1976 ◽  
Vol 34 ◽  
pp. 142-143
Author(s):  
Elizabeth F. Howell
Keyword(s):  
Plasma Membrane ◽  
Osmium Tetroxide ◽  
Buccal Cavity ◽  
Fiber Bundles ◽  
Microtubular Root ◽  
Stentor Coeruleus ◽  
Root Fiber

The ultrastructure of the normal oral apparatus of Stentor has not been extensively studied. I report here on the ultrastructure of the buccal cavity of Stentor coeruleus.Stentor coeruleus was fixed in either a buffered mixture of osmium tetroxide and glutaraldehyde, or in buffered glutaraldehyde alone. Cells were then dehydrated and embedded in a mixture of Epon and Araldite.An extensive adoral zone of membranelles surrounds the anterior of the cell, and each membranelle consists of 2 parallel rows of cilia. These extend down into the buccal cavity. Two microtubular root fibers, or nemadesmata (Figs. 2 and 5), extend deeply into the cytoplasm from the base of each ciliary kinetosome. Mitochondria are usually closely associated with the root fiber bundles, and small vesicles are present between the nemadesmata of adjacent kinetosomes (Fig. 5). In the cytopharyngeal, non-ciliated areas of the buccal cavity, microtubular ribbons which extend into the cytoplasm are aligned perpendicular to the plasma membrane of the buccal cavity (Figs. 1 and 2).

Vesicular system associated with spermiogenesis of bullfrog

1987 ◽  
Vol 45 ◽  
pp. 818-819
Author(s):  
K. C. Liu ◽  
S. F. Tsay
Keyword(s):  
Electron Microscopy ◽  
Microscopic Study ◽  
Electron Microscopic Study ◽  
Reproductive System ◽  
Seminiferous Tubule ◽  
Rana Catesbeiana ◽  
Routine Procedure ◽  
Electron Microscopic ◽  
Twisted Tubules ◽  
Electron Lucent

In the histologic and electron microscopic study of the male reproductive system of bullfrog, Rana catesbeiana, a vesicular system associated with spermiogenesis was observed. It appeared in the lumenal space of the seminiferous tubule (Fig. 1), in the heads of spermatids (Fig. 2), associated with the chromatins of the spermatid (Fig. 4). As deduced from sections, this vesicular system consisted of vesicles of various size or a large group of waving and twisted tubules (Fig. 3), After routine procedure of treatment for electron microscopy, the lumens of both of the vesicles and tubules were electron lucent.In human, vesicles and vesicular system associated with reproductive cell and tissue were reported. In abnormal spermiogenesis, flower-like body, actually vesicles, and giant vesicle associated with the head of spermatid were observed. In both cases the number of vesicle was limited from a single one to a few.

Direct Observation of Monolayer Zones in Al-wt 4% Cu

1990 ◽  
Vol 48 (1) ◽  
pp. 14-15
Author(s):  
B. Jouffrey ◽  
D. Dorignac ◽  
A. Bourret
Keyword(s):  
Solid Solution ◽  
Synchrotron Radiation ◽  
Direct Observation ◽  
Supersaturated Solid Solution ◽  
Original Model ◽  
X Ray ◽  
Image Position

Since the early works on GP zones and the model independently proposed by Preston and Guinier on the first steps of precipitation in supersaturated solid solution of aluminium containing a few percent of copper, many works have been performed to understand the structure of different stages in the sequence of precipitation.The scheme which is generally admitted can be drawn from a work by Phillips.In their original model Guinier and Preston analysed a GP zone as composed of a single (100) copperrich plane surrounded by aluminum atomic planes with a slightly shorter distance from the original plane than in the solid solution.From X-ray measurements it has also been shown that GP1 zones were not only copper monolayer zones. They could be up to a few atomic planes thick. Different models were proposed by Guinier, Gerold, Toman. Using synchrotron radiation, proposals have been recently made.

Sign in / Sign up

Export Citation Format

Share Document