Shell Movements Research Articles

Radiation scattering data on liquid metals

Abstract The scattering of radiation by liquid metals provides data on both the microscopic and the macroscopic properties of the metal. The macroscopic properties are obtained as a limit in which the momentum transferred by the radiation to the liquid is vanishingly small, while the microscopic structure and dynamical behaviour are obtained from data at higher momenta. An outline of the theory of radiation scattering will be given which emphasizes the relation between neutron and x-ray results. The possibility of studying electron shell movements by measuring the ratio of x-ray to neutron intensities is discussed. In general there are two types of experiment: those in which the intensity is measured as a function of the momentum transfer only (S(Q)), and those in which the intensity is measured as a function of both energy and momentum transfer (S(Q, θ)). The former experiments are used to obtain information on atomic positions while the latter experiments (coupled with the former) are used to derive dynamical information. Both kinds of experiment will be discussed and some methods of interpreting (S(Q)) and S(Q, θ)) will be described. The cooperative modes of motion in the system, particularly for wavelengths of the order of the spacing between atoms, may be observed as peaks in S(Q, θ). Several recent experiments of this kind on liquid lead will be discussed, particularly those in which the temperature variation was studied. In addition, information on the velocity correlation function for the metal atoms may be obtained. The spectral density of the velocity correlation will be considered and compared to predictions based on the cooperative mode picture. It is concluded that while much information has been obtained from these experiments there is a more detailed and extensive work to be done with both neutrons and x-rays.

Radiation scattering studies of the structure and transport properties of liquids

The use of radiation scattering techniques to study problems in liquid state physics has several advantages. These include the detailed nature of the information which can be obtained on structural and dynamical properties, the definiteness of the interpretation which may be given to the data and the exceedingly wide range in types of sample and experimental circumstances which can be covered. To deploy these advantages to the full requires powerful sources and special experimental methods which are still under development. A review is given of the techniques and theory of radiation scattering work emphasizing the relation between neutron and X-ray methods. The possibility of studying electron shell movements by measuring the ratio of X-ray to neutron intensities is discussed.

An apparatus for recording the water-pumping behaviour of lamellibranchs

An improved method of recording the water pumping activity o lamellibranchs is described and discussed. The excurrent water current of the experimental animal is isolated by the use of a rubber cone in a constant level chamber and passed through a continuously recording flowmeter into a dumping device which records the passage of a fixed volume. Together with a record of shell movements this gives a detailed record of water pumping activity. The apparatus has been used on oysters, Ostrea edulis, and mussels, Mytilus edulis. The experimental treatment of animals does not appear to affect this behaviour. The advantages of a continuous flowmeter record are discussed and illustrated.

The Feeding Behavior of the Seastar Evasterias troschelii Stimpson

Kymograph recordings of shell movements of 4.0–5.5 cm long clams (Protothaca staminea) during attacks by the seastar (Evasterias troschelii) showed: (1) in 21 experiments the valves were pulled apart at a mean rate of about 1.0 mm per minute, as measured at the mid‐ventral edge of the clams; (2) clams constantly tried to close during the initial opening of them by the seastars and then at longer intervals thereafter for a period usually not exceeding 4 hours.A specially constructed, false lucite “clam” containing Mytilus meat as bait was opened by Evasterias against known resistances applied to the approximate center of the upper, free‐moving valve of the “clam.” Kymograph recordings of shell movements of this “clam” during seastar attacks showed: (1) the curves showing the openings agree closely with those showing openings of live clams; (2) an average sized Evasterias may exert forces in excess of 5000 grams; (3) having lifted such weights, the seastar may hold them lifted for several hours; (4) in 14 experiments, weights varying from 700 to 5500 grams were lifted at an average speed of about 0.8 mm per minute, equal to an increase in gape of about 1.2 mm per minute during the lift. Maximum lifts varied from 2.8 to 13.5 mm with a mean of 6.6 mm.Experiments and observations showed that only the longitudinal musculature of the tube feet is responsible for the forces exerted by the seastar in opening bivalves. However, there are strong indications that the seastar is capable of “locking” itself in a rigid state before commencing the pull.If prevented from applying force, Evasterias will still succeed in feeding on bivalves, but the digestion period is considerably prolonged due to difficulties in inserting all lobes of the stomach into the prey.

STUDIES ON SHELL FORMATION. V. THE INHIBITION OF SHELL FORMATION BY CARBONIC ANHYDRASE INHIBITORS ,

1. The carbonic anhydrase inhibitors 2-benzothiazolesulfonamide (Cpd. I) and 2-acetylamino-1,3,4-thiadiazole-5-sulfonamide (Diamox) (Cpd. II) markedly reduced the rate of deposition of calcium in the shell of the oyster Crassostrea virginica. Treatment of oysters with Cpd. I, 1:80,000, for 7-8 hours reduced the rate to one-tenth the normal value and gave essentially complete inhibition at higher concentrations. The latter result indicates that inhibition by this compound is not limited to carbonic anhydrase. With Cpd. II the maximum inhibition was 50% and was produced at a concentration of 1:100,000 or higher.2. Measurements of shell movements and oxygen consumption of mantle tissue showed that concentrations of carbonic anhydrase inhibitors which had a marked inhibitory action on calcium deposition exerted no general toxic action on the oyster.3. The rate of calcium deposition of the oyster was more than 9 times that of the isolated mantle-shell preparation, confirming an earlier study. The addition of 0.01 M oxaloacetate to the mantle-shell preparation increased the deposition rate more than 4-fold, suggesting the utilization of metabolic CO2 for shell carbonate by the organism. Succinate and malate were without significant effect on calcium deposition.4. The experimental findings support the view that carbonic anhydrase increases calcium deposition in the oyster when the rate is sufficiently high that either of the following reactions becomes limiting: CO2 + H2O→H2CO3; CO2 + OH-→ HCO3-. At lower rates the enzyme would not be required.

Osmoregulation in Australian Freshwater Mussels (Lamellibranchiata). I. Water and Chloride Ion Exchange in Hyridella australis (Lam.)

The chlorinities of the blood and pericardial fluid of H. australis are similar, but always exceed those of the normal external medium. A study of blood chloride changes in mussels in media of different concentrations has shown that immediately following a change of medium there is a change in blood chlorinity, which tends to assume a new equilibrium level within 24 hr. The rapidity with which this change occurs depends upon the difference between the chlorinity of the blood and that of the external medium. A study of water exchange under identical conditions has shown that significant changes occur in the hydration of the mussel. In hypotonic media the mussel can regulate its water content; in hypertonic media it cannot, but its hydration assumes a new level within 24 hr. It is concluded that some part of the body surface is permeable to both salts and water. The urine of the mussel is hypotonic to the blood; it remains remarkably stabre in chlorinity despite changes in blood chlorinity. The role of the kidney as a regulating organ is discussed. The significance of shell movements in osmoregulation is demonstrated. Shell closure has been shown to be an effective seal from the external medium, allowing the mussel to resist desiccation.

Shell Movements of the Freshwater Mussel, Hyridella australis Lam. (Lamellibranchiata)

An analysis of about 4,500 hours of shell movement tracings of the freshwater mussel, Hyridella australis Lam., is presented. Nine series of experiments have been conducted, representing variations in light and temperature conditions. It has been found that, as well as shell movements, shell position or degree of openness must be considered. The shells may be closed (phase 1), completely open (phase 3), or stationary, intermediate between the two (phase 2), for the validity of which position mathematical proof has been found. The characteristics of each phase have been outlined. Temperature, within the range 17 to 27°C shows no well-definded influence on shell movements or the degree of openness. The influence of light, especially in regard to phase 2, is discussed. A diurnal light rhythm is associated with a diurnal feeding rhythm; under continuous illumination the shells tend to remain apart but in phase 2, darkness suppresses shell movements and feeding. The shell movements during ovulation are discussed.

EFFECT OF TEMPERATURE UPON SHELL MOVEMENTS OF CLAMS, VENUS MERCENARIA (L.)

1. A new apparatus, by means of which the shell activities of many bivalve mollusks can be measured and recorded, is described. 2. The analysis of 399 daily records of shell activities of 47 clams, subjected to temperatures ranging from — 1.0° to 28.0° C., showed that the length of time which the animals remain open partly depends upon the temperature of the surrounding water. 3. For the majority of clams hibernation begins soon after the water temperature decreases to 5.0° and 6.0° C. At lower temperatures the clams may remain completely closed for very long periods. No shell movements were exhibited, and no disposal of ejecta occurred. 4. Within the temperature range of 3.9° to 10.9° C., the average period of openness increased from 4 to 88 per cent of the total time, showing a correlation with the rise of temperature. 5. There was no correlation between the duration of openness of the clam shells and the temperature increase from 11.0° to 27.9° C. Within this temperature range the shells were open from 69 to 90 per cent of the total time, but the percentage did not increase simultaneously with the increase of water temperature. 6. The highest percentage of time open was recorded at temperatures 21.0° to 22.0° C., when the clams remained open 90 per cent of the total time, or 21 hours and 36 minutes per 24-hour period. 7. Small changes in the temperature of the surrounding water did not influence the shell movements of clams. 8. There appeared to be no definite periodicity in the clam shell movements. During brief intervals, the shell movements may be of a periodic type and exhibit a rhythmic character, but generally they appeared to be unsystematic and inconsistent. 9. There were considerable individual variations in the behavior of clams kept under identical environmental conditions. 10. Under the conditions of the experiments no definite correlation between the stages of tide and the shell movements of the animals could be detected. 11. The animals were closed for somewhat longer periods in daytime than in darkness.

On the feeding habits of oysters.

Studies of the feeding habits of oysters have been in progress since the spring of 1919 to determine: (1) the duration of active filtration of water, and (2) the effects of salinity, temperature, light, food content, and turbidity of the water upon the rate and the extent of feeding. The animals were studied while lying on an oyster reef in their natural environment. By means of recording apparatus continuous kymograph records of all shell movements of the oysters for over 2 months were obtained. Water samples were taken at regular intervals of time and tide, and in addition whenever the animals closed completely or opened after a period of closure in excess of 2 minutes.1The investigations have been carried on in several different environments, under widely varying conditions, and warrant the following conclusions:1. With the water temperatures of late spring, summer, and early fall oysters are active throughout most of the day and part of the night. At temperatures above 20° C. New Jersey natural oyster...