Scanning electron microscopic observations of the pulsed carbon dioxide laser effect on human enamel support microradiographic findings and indicate that this laser is significantly more efficient than the ruby laser within the limits of this investigation. Surface changes which were suggestive of fusion occurred between energy densities of 13 to 50 joules per square centimeter.There may be several potential applications of laser energy to dentistry. Initially, the use of the laser as a replacement for the dental drill was a popular idea,' but because of the high energy densities required this does not seem practical and has not been explored scientifically. Laser application to spectroscopic analysis of the chemical composition of substances related dentally has been attempted2?3 but still seems to be premature. The dental laboratory use of laser energy to solder and weld is in an early stage of development.4 In studying the effect of low laser energy densities, our interest has been ap-

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Mineralized plaques, which develop at the site of repeated subcutaneous injections of 100 mug KMnO4/0.2 H2O in rats, were investigated by electron microscopy. The newly formed, delineated, white plaque tissue at the injection site consisted of numerous, mostly unaltered fibroblasts and collagen fibers, without participation of inflammatory cells. Some signs of cell injury were found in the center of the lesions. Numerous, irregularly distributed, small, mineralized foci were seen near the fibroblasts. These were formed by aggregation of small needle-like units (50 A in diameter and 0.05-2.0 mum long). These needle-shaped units were found either in vesicular, cell derived structures, considered to be shed cell fragments, or on collagen fibers. Intramitochondrial deposits of such needle like units were seen frequently. Fusion of smaller mineralized foci to larger plaques occured and then needle-shaped units were seen at the periphery of the electron-dense lesions. Hypotheses concerning the mechanism of experimental cutaneous calcinosis (soft tissue mineralization) are discussed and related to the findings of this study. Probable intracellular crystal deposition and mineralization in cell-derived structures were shown for the first time in topical cutaneous calcinosis.

Einkristalle wurden auf Oxydschichten von Cu, Pb, Messing, Monel, V2A‐Stahl, verzinntem und verzinktem Eisen Licht und elektronemmikroskopisch sowie durch Elektronenstrahl‐ und Röntgenstrahlbeugung untersucht. Der heterogene Schichtaufbau von Eisenoxyden in Dampfkesselrohren aus niedrig legiertem Stahl wird elektronenoptisch bestimmt. Die jeweils günstigsten Bildungsbereiche der Whisker wurden in Abhängigkeit von der Temperatur beschrieben. Neben der Ausbildungsform wurde auch die kristallographische Wachstumsrichung von einigen Oxydnadeln bestimmt. Mit Hilfe der Elektronen‐ und Röntgenstrahlbeugung erfolgt eine kristallchemische Identifizierung der Oxydationsprodukte. Bei Anwesenheit mehrerer Metallkomponenten zeigen die Oxydwhisker eine selektive Oxydation, z.T. in Abhängigkeit von der Reaktionstemperatur. Die Oxydnadeln wachsen an der Spitze, und die Metallionen wandern in einer quasi flüssigen Schicht entlang der Kristalloberfläche. Bei Sulfiden wird Material auch über die Dampfphase transportiert. Nach unseren Untersuchungen wachsen die CuO‐Nadeln linear mit der Zeit. Bei der Oxydierung von Eisen an Luft bilden sich α‐Fe2O3‐Whisker, während im Dampfkesselbetrieb vorwiegend isometrische Fe3O4‐Kristalle entstehen. In Einzelfällen konnte nachgewiesen werden, daß sich α‐Fe2O3 auch aus Fe2O4 bilden kann. In Dampfkesselrohren f and sich neben dem Hauptoxyd aus Fe3O4 an der Grenze Metall/Oxyd eine bis zu einigen 100 μm dicke FeO‐Schicht.