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SUMMARY: The serum-protein determination method of Robinson & Hogden (1940), using the biuret reaction, has been applied to the determination of small quantities of bacteria. This 'direct protein' estimation involves about threequarters of the total protein of the bacteria.When a suspension of coliform bacteria, suitably washed and suspended in distilled water or saline, is treated with sodium hydroxide and copper sulphate, according to the method of Robinson & Hogden (1940) for the determination of serum proteins, and the excess of copper hydroxide removed by centrifugation, a clear purple solution is obtained. The intensity of the colour is linearly proportional to the quantity of bacteria present over a wide range, and its measurement in the Spekker photoelectric absorptiometer provides a rapid and accurate means of determination. The method has proved most useful for small quantities of bacteria, as a micro-method using the 0-5 ml. cells of the absorptiometer. When enough material is available, the larger (10 ml.) cells of the absorptiometer may be used with some gain in accuracy.Some other groups of bacteria, and yeasts, do not react in this way, but give a biuret colour which is chiefly bound to the cells. In these cases (e.g. Staphylococcus aureus; 'baker's yeast') the biuret colour may be obtained in soluble form if the mixture of bacteria and sodium hydroxide be heated in a boiling water-bath for a few minutes and then cooled, before the addition of the copper sulphate. EXPERIMENTALPreparation of suspensions. The suspensions were prepared without special treatment for use in various enzyme studies. Liquid cultures were centrifuged, the bacteria suspended in distilled water and filtered through glass wool, recentrifuged and finally resuspended in distilled water. From solid media the bacteria were removed by gentle shaking with distilled water, the suspension filtered through glass wool, centrifuged and the bacteria washed once and again resuspended in distilled water. Calibration of the absorptiometer scaleA series of volumes of a bacterial suspension containing up to 5 mg. dry weight of bacteria was measured out into small test-tubes, water added to make each sample up to 1-65 ml., and each treated with 0.3 ml. 20 yo (w/v) NaOH, and then 0.05 ml. 25 % (w/v) CuSO,. 5H20 solution. The copper hydroxide precipitate so obtained was broken up with a glass rod, and the

OUR knowledge of the metabolism of the bacteria of the genus Clostridium (the strict anaerobes) is at present very scanty. It has been recently reviewed [Topley and Wilson, 1929; McLeod, 1930; Stephenson, 1930], so only a brief summary will be given here, including facts discovered since the above reviews were published. Special reference will be made to Cl. sporogenes, which has been used by many workers as a type species, and of which our knowledge is the fullest. The present position is as follows. (1) These bacteria cannot grow in media containing an appreciable concentration of free oxygen. The degree of tolerance to low concentrations of oxygen varies from species to species. With regard to the reason for this lack of tolerance of oxygen no final decision has been reached. McLeod and Gordon [see McLeod, 1930] claim that it is due to production of hydrogen peroxide, while Quastel and Stephenson [1926] believe that oxygen acts by preventing the culture from reaching a sufficiently low oxidation-reduction potential. (2) They are unable to grow except in media containing protein or aminoacids. Carbohydrates, if present in addition, are fermented, but are neither sufficient nor essential for growth. (3) A compound containing the-SH group, or one from which the bacteria can produce an-SH group, is essential for growth (Quastel and Stephenson

THE earliest work dealing with the bacterial decomposition of formic acid was that of Hoppe-Seyler [1876], who dealt with its decomposition into carbon dioxide and hydrogen by mixed cultures obtained from mud, and showed that calcium formate was decomposed according to the equation

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