The infectivity and morphology of vesicular stomatitis virus (VSV) were studied after density gradient centrifugation in cesium chloride (CsCI), potassium tartrate (KT), and sucrose. Centrifugation in CsCl revealed two equally infectious bands corresponding to densities of 1.19 and 1.22 g/ml, and a third (density, 1.26 g/ml) band of low infectivity. Two bands (densities of 1.16 and 1.18 g/ml) were observed in the KT gradient, in which the lighter band contained most of the infectivity. Centrifugation in sucrose resulted in a single broad infectious band (density, 1.16 g/ml). The typical rodshaped VSV particles were found mainly in the lighter bands obtained in CsCl (1.19 g/ml) and KT (1.16 g/ml) and in the single sucrose gradient band (1.16 g/ml). Bent particles equally as infectious as the rod-shaped particles were a constant finding in the CsCl preparations, and were observed mainly in the second band (density, 1.19 g). Numerous strands 15 m,u wide were found in the third CsCl (density, 1.26 g/ml) and the second KT (1.18 g/ml) bands. Similar strands could be liberated from VSV particles after treatment with deoxycholate. Internal transverse striations were found to be a regular feature of VSV particles examined with the pseudoreplication negative-staining technique. For crude virus stocks, the physical particle-toinfectivity ratio ranged from 73 to 194. Several morphological similarities between VSV and myxoviruses were observed, including 10 m, surface projections, pleomorphic morphological forms, and 15 mMi seemingly nucleoprotein strands.

Potent antisera of high specificity and sensitivity were produced, in goats, to purified Australia antigen (Au). The antigen was prepared by one of three methods: (i) pelleting, low pH treatment, isopycnic centrifugation two times in CsCl, and rate zonal centrifugation in sucrose; (ii) same as procedure i, with the exception of the low pH treatment; or (iii) twice banding in CsCl by using a BXIV batch-type zonal centrifuge rotor with subsequent preparative Pevikon electrophoresis. The goat anti-Au sera contained high levels of precipitating antibody as tested by immunodiffusion in agar gel and discontinuous counterimmunoelectrophoresis (DCIE) as well as specific complement-fixing antibody and could be used for routine screening of sera for Au without prior adsorption with Au-negative normal human serum (NHS). Identification of 66 of 70 positive specimens (94.3%) in a panel of 98 coded sera (49 duplicates) with 100% reproducibility was made by using one of the goat anti-Au sera at a dilution of 1:16 in the DCIE method. No false positives were recorded. Low levels of antibody against NHS components were effectively removed by a single adsorption with glutaraldehyde cross-linked NHS.

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