The behavior of a Gaussian ultrasonic beam incident on a liquid-solid interface at the Rayleigh angle, the angle at which surface waves are excited on the interface, has been studied in some detail. The reflected beam is displaced in the manner predicted by Schoch; however, the ’’Schoch displacement’’ in general is too large. Good agreement is obtained between experimental results and the theory of Bertoni and Tamir, which assumes that the incident beam couples resonantly into a leaky surface wave at the Rayleigh angle and that the energy reradiated from this leaky surface wave interferes with specularly reflected energy. The propagation distance of the ultrasonic beam is explicitly included in describing the ultrasonic wave reflection at the Rayleigh angle.

This study identified mucus granules, determined mode of release and quantified their volume in the gallbladder epithelium of Richardson's ground squirrels (Spermophilus richardsonii) fed a lithogenic diet of 2% cholesterol to experimentally induce gallstone formation. Tissue was examined using light microscopy histochemistry, scanning and transmission electron microscopy, as well as autoradiography and morphometry at the electron microscopic level. Autoradiography demonstrated incorporation of a glycoprotein precursor, [3H]galactose, within the membrane-bound granules localized in the supranuclear region of the epithelial cells. Exocytosis of granule contents was by merocrine secretion. Morphometry indicated a significant increase in the amount of intracellular mucin granules as early as 18 hr on the lithogenic diet, a feature that continued throughout the experimental period of 20 weeks. Mucus synthesis/secretion rates returned to control values within 3 weeks after removal from the diet. Scanning electron microscopy observations revealed a thick sludge-like layer overlying the epithelium at a time in the chronology of the cholelithiasic model that correlated well with the initial phases of stone formation. Histochemistry showed this layer to be a mixture of acidic mucins. Neutral mucins were not observed. The hypersecretion of mucus and formation of this sludge-like layer appear to be critical nucleating factors in the formation of cholesterol gallstones.

The muscle layer of the canine gallbladder wall and cystic duct was found to be a three-dimensional meshwork of smooth muscle bundles which appear loosely and irregularly arranged on the mucosal aspect and consolidate to form a homogeneous plate-like layer on the serosal aspect. The muscle bundles are tightly woven around interspersed pockets of loose connective tissue in the gallbladder wall and gradually become loosely arranged with more prominent amounts of intervening connective tissue in the cystic duct. The muscle layer is thickest in the gallbladder wall and becomes progressively thinner out into the cystic duct. No anatomic sphincter was observed. Ultrastructural organization revealed individual muscle fibers to be of irregular profile, often branching, widely spaced with intervening collagen fibers, and having few cell-to-cell contacts.

The effects of time and of indomethacin on contractile responses of the guinea‐pig gall bladder were studied in vitro. The tissues contracted to field stimulation at 5 Hz (in the absence and presence of atropine 10−6 m), (‐)‐noradrenaline (10−5 m), acetylcholine (10−5 m), and adenosine 5′‐triphosphate (ATP, 10−4 m); the magnitude of the contractile responses increased with time. (‐)‐Isoprenaline 10−5 m either relaxed (17 of 23 preparations tested) or had no effect on gall bladder strips. The responses of strips of guinea‐pig gall bladder to field stimulation at 5 Hz (in the absence or presence of atropine 10−6 m), (‐)‐noradrenaline (10−5 m), and acetylcholine (10−5 m) obtained 4 h 45 min after setting up the tissue were reduced following incubation with indomethacin (7.9 times 10−6 m for 1 h). The responses to (‐)‐isoprenaline (10−5 m) and to ATP (10−4 m) were abolished by incubation with indomethacin. These results suggest that, in the guinea‐pig gall bladder in vitro, the magnitude of the contractile responses to field stimulation at 5 Hz, (‐)‐noradrenaline (10−5 m), and acetylcholine (10−5 m) and the ability of the tissue to respond to (‐)‐isoprenaline (10−5 m) and ATP (10−4 m), may be dependent on the synthesis of a prostaglandin‐like substance.

Richardson's ground squirrels (Spermophilus richardsonii) of both sexes were fed a 2 per cent cholesterol-enriched diet for intervals of 12, 18, and 24 h; 3, 5, and 7 days; and 2, 3, 10, and 20 weeks. It was shown that free (unesterified) cholesterol, phospholipid, and cholesterol ester accumulated in specific regions of the gallbladder mucosa during cholelithiasis. Electron microscopy revealed the presence of lipids inter- and intracellularly as early as 12 h after ingestion. By 7 days, lipids were seen in dilated endoplasmic reticulum, as well as in supranuclear and basal regions of epithelial cells. Histochemical localization revealed free cholesterol in dilated endoplasmic reticulum and residual bodies at the ultrastructural level. Neutral lipid was observed by light microscopy in the supranuclear and basal regions of the cells. In 10- and 20-week treated animals, lipid droplets were also seen in the lamina propria and macrophages. The lesion induced by cholesterol ingestion persisted throughout the experimental period, and while different from that in human tissue, it was similar to those observed in experimental canine cholesterosis.