Microstructure Formation in Pb-30wt.%Bi Peritectic Alloy

A rich variety of two-phase microstructures have been shown to form in the directionally solidified Pb-30wt.%Bi alloy. The selection of microstructure is shown to be depended upon the value ofG/V(temperature gradient in the liquid divided by growth rate). The microstructure evolution is also discussed based on the competitive growth of different phase at variousG/Vratios in directional solidification. Experimental results indicate that the primary a phase is the leading phase and grows with a dendritic/cellular microstructure while the peritectic b phase grows with cellular/planar microstructure in interdendritic/intercellular region at lowG/Vvalue. In contrast, competitive structures but not the discrete banded structure is present at highG/Vratio which makes the primary and secondary phase to grow with planar/cellular interface.

Effects of acute doses of sodium fluoride on the morphology and the detectable calcium associated with secretory ameloblasts in rat incisors.

Fluoride in high concentrations is known to have an adverse effect on the formation of enamel. The effect of a single injection of two concentrations of sodium fluoride on inner enamel secretory ameloblasts was investigated morphologically by electron microscopy and functionally by assessing the location and relative amount of available calcium, using the potassium pyroantimonate method. The results showed that acute doses of fluoride interfere with the normal function of secretory ameloblasts. The increase in the population of lysosome-like structures observed after fluoride administration is suggestive of defects in the synthetic pathway. Concomitant with the effect of fluoride on secretory ameloblasts is an inhibition of enamel formation, resulting in incomplete enamel rods and leaving large remnants of Tomes' processes buried in the enamel. The distribution of the calcium pyroantimonate deposits found tends to support the concept of calcium traveling between the cells to the enamel. Acute doses of fluoride also reduce the amount of calcium available for complexing with pyroantimonate in the intercellular region.

A transmission electron microscopic study of porcine stratum corneum treated with topical applications of glycolipid

The mammalian epidermis forms a differentiated surface layer termed the stratum corneum (sc) which represents the principal barrier. It is now known that the permeability barrier is located in the intercellular region of the sc and consists largely of neutral lipids derived from glycolipids that are aligned to form a highly hydrophobic structure. It is possible that this barrier might be augmented by topical application of pure glycolipid, which could diffuse through the regions between the squarnes. We have examined this possibility by treating the backskin of pigs with glycolipids and then preparing the tissue for examination with the transmission electron microscope (TEM).

Gregarine attachment organelles — structure and permeability of an interspecific cell junction

The junction between the gregarine trophozoiteNematocystis magnaSchmidt and an epithelial cell of its earthworm hostLumbricus terrestrisMuller consists of an extensive folding and meshing of the single trilaminar membrane bounding the host cell and the complex folded multilaminar limiting membrane of the trophozoite. They are separated by a structureless intercellular region of some 50 nm in width. Specialized communicating regions or permeable elements were not observed. Transport of a radioactive label across non-junctional and junctional membranes was demonstrated by using tritiated glucose. The attachment organelle of the trophozoite is shown to be capable of allowing metabolites to pass into the cell directly from the host tissue.

Cell relationships in Hymenolepis diminuta

SUMMARYThe intimate cell relationships of Hymenolepis diminuta are described and occur between cells of the parenchyma, excretory system, muscle and tegument. The cell relationships are of three types: (a) a tight junction or zonula occludens; (b) a desmosome-like structure without tonofibrils or intercellular dense line; (c) a junctional complex with modified unit membranes and an intercellular region of dense granules and fibres.This research was begun while one of us (L.T.T.) was a Visiting Lecturer in the Biology Department, Rice University, and completed in the Zoology Department, Queen's University, Belfast. We should like to thank Dr C. W. Philpott for allowing us the full use of the facilities of his electron-microscope unit and Mr W. Ferguson for photographic assistance.

Electron Microscopy of the Ovary of Fasciola Hepatica

The external wall of the ovary of Fasciola hepatica is a membrane-like structure in contact with a non-cellular material in the ovary. An intercellular region containing an amorphous material of moderate electron density is present in the ovary. The primary oocytes are provided with peripheral processes that extend into the intercellular region. The oocytes do not proceed beyond the prophase of the first meiotic division until after they leave the ovary. The nucleolus of the primary oocyte contains vacuole-like areas and emits granular material to the nucleoplasm; some of this material may move to the cytoplasm. Pores are present in the nuclear envelope. In older oocytes narrow bridge-like structures connect the nucleolus and the nuclear envelope. The nuclear envelope of the primary oocyte undergoes replication. It is continuous with the endoplasmic reticulum and the plasma membrane. The location of the mitochondria is correlated with the phases of growth of oogonia and oocytes. The mitochondria possess irregularly arranged cristae. Small, round or oval nutritive bodies are present in the peripheral cytoplasm of older oocytes. It is suggested that areas of relatively high density containing vacuole-like structures represent the Golgi complex.