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The fine structure of smooth muscle cells of the embryo chicken gizzard cultured in monolayer was studied by phase-contrast optics and electron microscopy . The smooth muscle cells were irregular in shape, but tended to be elongate . The nucleus usually contained prominent nucleoli and was large in relation to the cell body . When fixed with glutaraldehyde, three different types of filaments were noted in the cytoplasm : thick (150-250 A in diameter) and thin (30-80 A in diameter) myofilaments, many of which were arranged in small bundles throughout the cytoplasm and which were usually associated with dark bodies ; and filaments with a diameter of 80-110 A which were randomly orientated and are not regarded as myofilaments. Some of the aggregated ribosomes were helically arranged . Mitochondria, Golgi apparatus, and dilated rough endoplasmic reticulum were prominent . In contrast to in vivo muscle cells, micropinocytotic vesicles along the cell membrane were rare and dense areas were usually confined to cell membrane infoldings . These cells are compared to in vivo embryonic smooth muscle and adult muscle after treatment with estrogen . Monolayers of cultured smooth muscle will be of particular value in relating ultrastructural features to functional observations on the same cells .

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Biocompatibility tests have been compared for their suitability as routine safety tests for urinary catheters. Latex catheters from five manufacturers were tested by each of the following four methods: (1) a cell culture cytotoxicity assay of catheter extracts, (2) intracutaneous injection of the extracts into rabbits, (3) intramuscular implant of catheter pieces into rabbits, (4) catheterization of sheep (mucous membrane irritation). The rabbit intracutaneous and intramuscular tests are both current pharmacopoeial methods for ascertaining the suitability of polymers for medical use. The four tests each showed a cell or tissue response ranging from no detectable change to severe damage, according to the catheter batch or brand, and they each identified the same samples as most toxic and least toxic. However, they differed in sensitivity. The sheep test and the cell culture assay discriminated between catheters of intermediate toxicity and ranked as toxic catheters not identified as such by the two pharmacopoeial tests. The sheep test most closely approximates clinical usage, but is impractical for routine use. The cell culture assay is a suitable alternative. It also has the advantages of a clearly defined endpoint, good sensitivity, reproducibility, speed, and reduced animal usage.

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