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The immune IgM-like macroglobulins were isolated from three species of bony fishes (Ictalurus punctatus, Lepisosteus osseus, and Polyodon spathula) representing the three orders of the subclass Actinopterygii. These macroglobulins were found to have sedimentation coefficients of 14 S and molecular weights of 600,000-630,000. The carbohydrate compositions were determined and found to be different from that of human macroglobulins. After reduction and alkylation, the heavy and light chains could be separated by gel filtration and were found to have molecular weights of approximately 70,000 and 23,000 respectively. The amino acid compositions of these chains were similar to those of mammalian IgM heavy and light chains. The macroglobulins were found by electron microscopy to have a tetrameric structure, in contrast to the pentameric structure found in mammalian, chicken, and shark IgM, i.e. in species later on the evolutionary scale.

The observation that the relative viscosity of synovial fluid obtained from patients with joint effusion associated with connective tissue diseases is decreased has stimulated a number of investigations directed towards the characterization of the nature of this alteration. Since the relative viscosity of synovial fluid is a function both of the concentration ofhyaluronic acid and ofits degree ofpolymerization elucidation of this problem is predicated on the determination of both of these parameters. Earlier studies have dealt primarily with the differences in hyaluronic acid concentration (Decker, McGuckin, McKenzie, and Slocumb, 1959), or with the comparison of relative viscosities at an arbitrarily chosen concentration (Fletcher, Jacobs, and Markham, 1955). These results indicated that the hyaluronic acid concentration is decreased and suggested that the polysaccharide was depolymerized in synovial fluids obtained from patients with rheumatic diseases.Sundblad (1953) later demonstrated the usefulness of intrinsic viscosity determinations as a measure of the degree of polymerization of hyaluronic acid in human synovial fluid. He calculated the hyaluronic acid concentration of synovial fluid from the glucosamine concentration, which was determined by a modification of the Elson-Morgan procedure, after hyaluronidase digestion followed by trichloroacetic acid precipitation of the proteins. The intrinsic viscosity was calculated from the results of a series of relative viscosity determinations made at different dilutions of the fluid in a phosphate buffer, at pH 7 0, ionic strength 0-20 (OsO8 phosphate + 0-12 sodium chloride), and a temperature of 370 C. Balazs and Sundblad (1959) have shown that the presence of serum proteins does not appreciably influence the viscous behaviour of hyaluronic acid.

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