Showing papers by "McGill University published in 1969"

The deformation of a drop in a general time-dependent fluid flow

Abstract: A theoretical method is given for the determination of the shape of a fluid drop in steady and unsteady flows by making an expansion in terms of the drop deformation. Effects of fluid viscosity and interfacial tension are taken into account. Examples given include the determination of the shape of a drop in shear and in hyperbolic flow when each is started impulsively from rest.

On the mechanism of prograde metamorphic reactions in quartz-bearing pelitic rocks

Abstract: An empirical method is described whereby the sequence of textural changes in pelitic rocks from one zone to the next may be reconciled with the balanced metamorphic reaction inferred to have been in progress. It consists in deducing from the textures of a single thin section a set of metasomatic cation-exchange reactions, which proceed in different microscopic domains of the rock, but which add up on the scale of the whole thin section to give the balanced metamorphic reaction. Each metasomatic subsystem is closed to aluminum, but open to the more mobile cations, which are free to diffuse from one subsystem to another, subject to the requirement of short-range electrostatic neutrality, and to the assumption that the system is closed on the scale of the whole thin section. Evidence in support of the central postulate that aluminum is relatively immobile is found in 1. the preservation of bedding laminations, on a finer scale than the staurolite porphyroblasts which transect them without disrupting them. 2. The fact that quartz, the only abundant aluminum-free mineral in pelitic rocks, is by far the most common mineral in veins and “pressure shadows”. 3. The fact that the reactions so deduced provide reasonably precise descriptions of such common textures as the sillimanite needles in biotite and quartz, and the abundant quartz “inclusions” in staurolite.

Detection of complex carbohydrates in the Golgi apparatus of rat cells.

Abstract: Two methods used for the electron microscopic detection of glycoproteins were applied to a variety of cell types in the rat; one involved successive treatment of sections with periodic acid, chromic acid, and silver methenamine; and the other, a brief treatment with a chromic acid-phosphotungstic acid mixture. The results obtained with the two methods were identical and, whenever the comparison was possible, similar to those obtained with the periodic acid-Schiff technique of light microscopy. In secretory as well as in nonsecretory cells, parts of the Golgi apparatus are stained. The last saccule on one side of each Golgi stack is strongly reactive (mature face), and the last saccule on the other side shows little or no reactivity (immature face); a gradient of reactivity occurs in between these saccules. The more likely explanation of the increase in staining intensity is that carbohydrate is synthesized and accumulates in saccules as they migrate toward the mature face. In many secretory cells, the mature face is associated with strongly stained secretory granules. Other structures stained are: (1) small vesicles, dense and multivesicular bodies, at least some of which are presumed to be lysosomal in nature; (2) cell coat; and (3) basement membrane. The evidence suggests that the Golgi saccules provide glycoproteins not only for secretion, but also for the needs of the lysosomal system as well as for incorporation into the cell coat and perhaps basement membrane.

Identification of microglia in light and electron microscopy

Abstract: The corpus callosum of 60–80 gm male rats was processed by the weak silver carbonate method of del Rio-Hortega for the detection of microglia in the light microscope. Because of the opacity of the metal stain taken up by these cells, they could be recognized in the electron microscope. The characteristic features of microglia were thus found to be a small nucleus in which dark chromatin contrasts with light nucleoplasm, and a cytoplasm containing dense bodies (presumed to be lysosomes) and poor in endoplasmic reticulum. After gaining experience with microglia in the electron microscope, it became possible to recognize their features in 0.5–1 μ thick toluidine blue stained Epon sections examined in the light microscope. In the electron microscope, some microglia are found within expansions of the basement membrane of capillaries (pericytal microglia); they usually have little cytoplasm, few dense bodies and few processes. There is evidence that these cells can break out of their basement membrane enclosure and enter the brain tissue proper. There, they scatter singly between other cells and fibers. These cells (interstitial microglia) send of long processes. They may contain numerous dense bodies and be surrounded by irregular spaces (suggesting the existence of surface activity). These observations support the classical view of microglia as brain macrophages. Microglia constitute 5.5% of the glial population of the corpus callosum. After injection of 3H-thymidine and radioautography in the light or electron microscope, none showed labeling. Hence, it is presumed that microglia do not proliferate under normal conditions.

Radioautographic visualization of the incorporation of galactose-3h and mannose-3h by rat thyroids in vitro in relation to the stages of thyroglobulin synthesis

Abstract: Rat thyroid lobes incubated with mannose-3H, galactose-3H, or leucine-3H, were studied by radioautography. With leucine-3H and mannose-3H, the grain reaction observed in the light microscope is distributed diffusely over the cells at 5 min, with no reaction over the colloid. Later, the grains are concentrated towards the apex, and colloid reactions begin to appear by 2 hr. With galactose-3H, the reaction at 5 min is again restricted to the cells but it consists of clumped grains next to the nucleus. Soon after, grains are concentrated at the cell apex and colloid reactions appear in some follicles as early as 30 min. Puromycin almost totally inhibits incorporation of leucine-3H and mannose-3H, but has no detectable effect on galactose-3H incorporation during the 1st hr. Quantitation of electron microscope radioautographs shows that mannose-3H label localizes initially in the rough endoplasmic reticulum, and by 1–2 hr much of this reaction is transferred to the Golgi apparatus. At 3 hr and subsequently, significant reactions are present over apical vesicles and colloid, while the Golgi reaction declines. Label associated with galactose-3H localizes initially in the Golgi apparatus and rapidly transfers to the apical vesicles, and then to the colloid. These findings indicate that mannose incorporation into thyroglobulin precursors occurs within the rough endoplasmic reticulum; these precursors then migrate to the Golgi apparatus, where galactose incorporation takes place. The glycoprotein thus formed migrates via the apical vesicles to the colloid.

The distribution of lignin in sprucewood as determined by ultraviolet microscopy

Abstract: The distribution of lignin in black spruce has been determined quantitatively by the study of 05 μm transverse sections in a UV microscope The average lignin concentration in the compound middle lamella was about twice that in the secondary wall The lignin concentration of the middle lamella at the cell corners of adjacent tracheids was nearly four times that in the secondary wall but the volume of the secondary wall was much greater than the volume of the middle lamella Thus, for earlywood, 72% of the total lignin was in the secondary wall leaving only 28% in the compound middle lamella and cell corner middle lamella regions The corresponding values for latewood were 82% and 18% respectively Use of oblique longitudinal sections of 01 μm thick permitted the resolution of the compound middle lamella The lignin concentration in the true middle lamella was found to be equal to that in the cell corner middle lamella and the primary wall lignin content to be about twice that in the secondary wall

Cortical inhibition and γ-aminobutyric acid

Abstract: 1. In cats under Dial, multiple micro-electrodes were used to analyze the changes in membrane potential and conductance of cortical neurones produced by inhibition (evoked by surface shocks) and by microiontophoretic applications of GABA. 2. IPSPs are associated with a marked but variable increase in membrane conductance. At the peak, the conductance may rise 3–4 fold. 52 estimates gave a mean increase of 54.0% (S.D. 77%). 3. The time course of the main increase in conductance coincides approximately with the time course of the IPSP and the period of reduced excitability. After an initial phase of very high conductance, the conductance diminishes exponentially with a time constant of about 50 msec. 4. GABA causes a very striking increase in membrane conductance and, in most cases, a negative shift in membrane potential. 5. Estimates of the reversal potential of the action of GABA (EGAB) agree well with estimates of the reversal potential for IPSPs (EI) obtained before or after the application of GABA. There was a strong positive correlation between values of EI and EGAB, and the slope of the line describing EI vs EGAB, did not differ significantly from 1.0 6. These observations therefore greatly reinforce previous evidence of a close identity between the actions of GABA and of the normal transmitter of cortical IPSPs. 7. The increase in conductance produced by GABA shows an initial peak (mean 17.1 n-mho/nA GABA current, S.E. 4.50, n=41) and then tends to fall, after 10–20 sec, to a relatively stable level (mean 9.31 n-mho/nA (S.E. 2.38, n=32)). This phenomenon is particularly evident with large doses of GABA. 8. A maintained application of GABA is usually associated with a change in EI towards greater positivity, probably owing to a large influx of Cl−.

The effect of tropolone on the formation of 3,4-dihydroxyphenylacetic acid and 4-hydroxy-3-methoxyphenylacetic acid in the brain of the mouse

Abstract: 1. The development of a very sensitive and specific fluorimetric assay for 3,4-dihydroxyphenylacetic acid has made it possible to measure how inhibitors of the enzyme catechol-O-methyl transferase affect the relative concentrations of this acid and its O-methylated derivative 4-hydroxy-3-methoxyphenylacetic acid (homovanillic acid) in the brains of mice treated with L-3,4-dihydroxyphenylalanine or probenecid.2. It was found that tropolone and tropolone-4-acetamide reduce the concentration of homovanillic acid in the brains of the treated mice to an extent dependent on the dose.3. The concentration of 3,4-dihydroxyphenylacetic acid in the brain was increased by the administration of tropolone or tropolone-4-acetamide but the dose and response were not simply related to one another.4. The results suggest that, in vivo, the formation of 3,4-dihydroxyphenylacetic acid is not always a simple alternative to the formation of homovanillic acid when the enzyme catechol-O-methyl transferase is inhibited.

Electron microscopic features and proliferation of astrocytes in the corpus callosum of the rat

Abstract: The gold chloride sublimate method of Ramon y Cajal was used to stain astrocytes in the corpus callosum of 60–80 g male rats. The opacity of the metal-stained astrocytes to the electron beam allowed their study in the electron microscope. It was thus found that metal deposits are absent from the nucleus but are present over two cytoplasmic structures: bundles of filaments and dense bodies. Once the features of astrocytes had been observed in metal stained preparations, it became possible to identify them in sections stained for electron microscopy by the routine uranyl-lead sequence. The presence of filament bundles in the cytoplasm was the most useful diagnostic feature. Dense bodies also helped. The nucleus was relatively large and light with a very distinct, often irregular nuclear envelope. The rather light cytoplasm contained glycogen granules, with few ribosomes and cisterns of endoplasmic reticulusm. However, a few otherwise typical astrocytes had fairly dark nucleus and cytoplasm. After gaining experience with the electron microscope, it was possible to identify most astrocytes in the light microscope by their nuclear features. Counts of the frequency of astrocytes using either the light or electron microscope revealed that they make up about one quarter of the glial population of the corpus callosum. The main properties of astrocytes seemed to be: (1) plasticity of the cell surface, which infiltrates all available spaces around it; (2) apparent rigidity of the bundles of filaments present in the processes, where they may play a supporting role; and (3) ability of astrocytes to undergo division, as demonstrated both by the uptake of 3H-thymidine into 1.7% of these cells and by the presence of mitotic figures.

Two classes of spermatogonial stem cells in the monkey (Cercopithecus aethiops)

Abstract: To analyze the behavior of spermatogonia in the monkey, the cytological features, topographical arrangement and frequency of the two classes of type A (A1, A2) and the four classes of type B (B1–B4) spermatogonia were determined in dissected tubules, fixed in Carnoy, stained with hematoxylin and mounted “in toto.” The capacity of spermatogonia to divide was also analyzed in radioautographed testicular sections from an animal injected with tritiated thymidine. The type A1 spermatogonia, characterized by nuclei containing deeply stained, finely granulated chromatin, were found to be non-dividing elements. The type A2 spermatogonia, characterized by nuclei showing palely stained, coarsely granular chromatin, all divided in stages IX–X of the cycle of the seminiferous epithelium to yield equal numbers of new type A2 cells and type B1 spermatogonia. The type B1, as the other type B cells, were characterized by nuclei containing granules or flakes of deeply stained chromatin. While the type A2 spermatogonia remained dormant until stage IX of the following cycle, the type B1 cells all divided during stage XII to yield twice their number of type B2 spermatogonia. These, in stage II, divided to give twice as many type B3, which, in stage IV, divided to produce twice as many type B4 spermatogonia. Lastly, in stage VI, the latter elements all divided to yield spermatocytes. Thus, the type A1 spermatogonia, did not appear to be actively involved in the production of spermatocytes and were tentatively considered as “reserve stem cells;” the type A2 spermatogonia, were identified as “renewing stem cells.”

Feature extraction: A survey

Abstract: A survey of computer algorithms and philosophies applied to problems of feature extraction and pattern recognition in conjunction with image analysis is presented. The main emphasis is on usable techniques applicable to practical image processing systems. The various methods are discussed under the broad headings of microanalysis and macroanalysis.

Coalescence of Two Immiscible Liquid Drops

Abstract: When two immiscible liquid drops suspended in a third immiscible liquid are brought into contact, three equilibrium configurations which depend upon the spreading coefficients are possible. Experiments for a large number of systems, including three phase emulsions, confirm the theory and indicate the mechanisms of reaching equilibrium.

A General High-Order Finite-Element Analysis Program Waveguide

Abstract: A very general computer program for determining sets of propagating modes and cutoff frequencies of arbitrarily shaped waveguides is described. The program uses a new method of analysis based on approximate extremization of a functional whose Euler equation is the scalar Helmholtz equation, subject to homogeneous boundary conditions. Subdividing the guide cross section into triangular regions and assuming the solution to be representable by a polynomial in each region, the variational problem is approximated by a matrix eigenvalue problem, which is solved by Householder tridiagonalization and Sturm sequences. For reasonably simple convex polygonal guide shapes, the dominant eigenfrequencies are obtained to 5-6 significant figures; for nonconvex or complicated shapes, the accuracy may fall to 3 significant figures. Use of the program is illustrated by calculating the propagating modes of a class of degenerate mode guides of current interest, for which experimental data are available. Numerical studies of convergence rate and discretization error are also described. It is believed that the new program produces waveguide analyses of higher accuracy than any general program previously available.

A framework for research on foreign policy behavior

Abstract: The study of foreign policy is underdeveloped ; its theoretical content is inadequate ; and analysis for the most part lacks rigor. Some preparatory work has been done. State behavior is no longer seen exclusively as a reaction to external stimuli; internal pressures, too, are now widely recognized as affecting foreign policy decisions. Yet, as James Rosenau has cogently observed, &dquo;to identify factors is not to trace their influence. To uncover processes that affect external behavior is not to explain how and why they are operative under certain circumstances and not under others. To recognize that foreign policy is shaped by internal as well as external factors is not

Origin and renewal of goblet cells in the epithelium of the mouse small intestine

Abstract: The epithelium of duodenum, jejunum and ileum was investigated in adult female mice given an injection of3 H-thymidine and sacrificed at times varying from one hour to 14 days later. The tissues were fixed by perfusion with paraformaldehyde and embedded in Epon. One micron thick sections were cut singly or serially, radioautographed and stained with iron hematoxylin and safranin O. In addition, reconstruction of a crypt was made from serial sections of jejunum. The reconstruction of a crypt shows the well known columnar, goblet, Paneth, and argentaffin cells. There are also little known cell types referred to as oligomucous and granulo-mucous and pale cells with or without mucus. Of these cells, the only numerous ones are the oligomucous cells, which are located in the lower half of the crypts and contain a few or even only one mucous globule. In the electron microscope, they display long cisterns of rough endoplasmic reticulum parallel to the lateral cell membrane and similar to those observed in goblet cells. In radioautographs of the crypts neither goblet cells, nor Paneth cells, nor argentaffin cells show mitosis or label one hour after3 H-thymidine injection. Granulo-mucous and pale cells are only rarely labeled. In contrast, columnar and oligomucous cells frequently take up label and undergo mitosis. By 12 hours after injection labeled goblet cells have appeared. Since at that time 3 H-thymidine has left the circulation, the label must have been acquired by transformation of labeled columnar or oligomucous cells. Furthermore, since transitional forms between oligomucous and goblet cells are common, it is concluded that oligomucous cells are those which directly transform into goblet cells. Eventually, like columnar cells, labeled goblet cells migrate to the villus epithelium, climb to the villus tip and fall into the lumen. Although oligomucous cells fit the requirements for goblet cell precursors, not enough of them are labeled to account for the rate of renewal of goblet cells. It is therefore speculated that some undifferentiated columnar cells at the base of the crypts participate in the production of oligomucous cells, which in turn yield goblet cells.

Seasonal Variation in Standing Crop and Species Diversity of Insect Communities in a small Quebec Stream

Abstract: Seasonal changes in the distribution and abundance of insects species were studied in a small cool woodland stream where the primary food material was fallen leaves. Between March 1966 and March 1967, weekly quantitative samples were taken from sand, gravel, stone, leaf, and leaf detritus habitats. The number of insects per unit area of each habitat was least in sand and increased through gravel, stones, leaves, and detritus. Biomass per unit area was least in gravel and increased through detritus, sand, leaves, and stone. The annual standing crop of the stream as a whole was approximately 3,000 insects/m2 and 2 g/m2 (dry wt.). The number of insect species in any one habitat varied according to apparent spatial heterogeneity of the environment, to substrate stability, and to food resources. Leaves supported the highest number of species (92), sand the least (61). Species diversity was higher during summer and winter than during spring and autumn. When compared with other aquatic environments, the bottom fauna of the stream has oligotrophic features, including a large number of species and an annual standing crop of poor to intermediate richness.

Intramural Pressure in the Left Ventricle of the Dog

Abstract: The pressure within a fluid pocket in the ventricular wall increases with the size of the pocket introduced. By observing the pressure in pockets of varying size, it is possible, by extrapolation, to estimate what the pressure would be in the absence of a pocket. This pressure varies from cavity pressure close to endocardium to ambient pressure close to the epicardium.