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Particulate preparations of both Mycobacterium tuberculosis and M. phlei contain almost all the respiratory activity, NADH oxidase, cytochromes, and glycophospholipid biosynthetic activity of the cells.'-4 Electron micrographs have shown that this preparation consists of cytoplasmic membrane fragments and small structures about the size of ribosomes.5 While this type of preparation has been described as a ribosomal fraction,6 direct inspection and enzymatic assays show these washed and centrifuged preparations to be variable mixtures of ribosomes, cytoplasmic membrane fragments, and cell walls. This study was begun in order to characterize further this particulate fraction. In this communication, we shall describe the preparation, properties, and fine structure of the ribosomes of the H37Ra strain of M. tuberculosis. Materials and Methods.-M. tuberculosis, strain H37Ra, was grown as surface cultures, as previously described.7 In a few experiments, the bacteria were grown in the same media in shake flasks. Escherichia coli B was grown in nutrient broth in shake flasks and harvested in the logarithmic phase. Mycobacterial cells were harvested at various ages and ground in a mortar for 5 mim with an equal weight of alumina. All operations were performed at 00-30C. In some experiments, the cell-free extract was prepared with a colloid mill.7 The resulting paste was suspended in 0.1 M tris(hydroxymethyl)aminomethane (Tris) (pH 7.5) and 0.01 M MgCl2, and centrifuged for 15 min at 25,000 X g to sediment the alumina, unbroken cells, and cell debris. The supernatant solution was recovered and centrifuged at 140,000 X g for 2 hr to sediment the ribosomes.8 The resulting pellet was resuspended in Tris-Mg++ buffer as before, washed once by centrifugation at 140,000 X g for 2 hr, and finally resuspended in Tris-Mg++ buffer (washed ribosomes).

A qualitative method for the isolation of cristobalite or of quartz from soils and sediments was developed for the characterization of these SiO2 polymorphs by X‐ray diffraction (XRD), scanning electron microscopy (SEM), and oxygen isotope analysis by mass spectrometry. The procedure, applicable to silt or sand size fractions, involved two steps. First the quartz was separated from the cristobalite by centrifugation of a polyvinylpyrrolidone (PVP) stabilized suspension in tetrabromoethane and nitrobenzene mixtures (specific gravity range from 2.28 to 2.38). Then selective chemical dissolution of the non‐SiO2 minerals was effected by HCl, NaOH, and H2SiF6 treatments. Minerals, such as magnetite, resistant to dissolution in these reagents, were subsequently removed by heavy liquid separation.Treatment of hydrothermal low‐cristobalite (Taiwan), having blocky SEM masses and δ18O = 14 ‰, with HCl, NaOH, and H2SiF6 removed amorphous silica and released the crystalline platelets of δ18O = 9 ‰. Little change in isotope abundance of the latter occurred on retreatment. When amorphous diatom skeletons (δ18O = 32.2 ‰) were treated with these reagents, 77% of the sample dissolved. The remaining skeletons had slightly lower δ18O value (29.1 ‰) but a similar diatom skeleton morphology by SEM.Quartz isolated from the A2 and Cl horizons of Parahaki soil of New Zealand had δ18O values of 9.6 to 10.0 ‰ The associated low‐cristobalite had δ18O = 8.3 to 9.1 ‰. The oxygen isotope data indicate that both of these SiO2 polymorphs had a hydrothermal or volcanic origin, and were not formed in the soil.