I953 activity of diphosphopyridinenucleotidase is greatly increased (Nason et al. 1951)-there is no reason to attribute invariably the disorders of metabolism which occur in zinc deficiency to a primary impairment of protein synthesis. Copper deficiency has been claimed to have marked effects on the protein metabolism of green plants (Gilbert, Sell & Drosdoff, 1946; Wood & Womersley, 1946; Lucas, 1948; Gilbert, 1951), and so the observation that the aldolase activity in the leaves of copper-deficient oats remains unimpaired, suggests that the lowered aldolase activity in the leaves of zinc-deficient oats is not due primarily to a decreased protein synthesis; although zinc might be specifically involved in the synthesis of the enzyme itself. The third possibility that the aldolases of green leaves are activated by Zn2+ or by zinc-containing co-enzymes is being examined. SUMMARY Aldolase activity was found to be materially decreased in tissue suspensions prepared from the leaves of zinc-deficient plants of Trifolium subterrane,um and of Avena 8ativa, but was unchanged by copper deficiency. The author is grateful to K. Powrie for supplying some of the experimental material: to G. B. Jones for the polarographic estimation of zinc and copper and to V. Stephen who set up the aeration apparatus and is particularly indebted to H. R. Marston, F.R.S., Chief of the Division of Biochemistry and General Nutrition, C.S.I.R.O., for his advice and criticism during the experiment and his help in preparation of the manuscript. Glasshouse accommodation was made available by Prof. J. G. Wood of the Botany Department of the University of Adelaide, and this courtesy is gratefully acknowledged.

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Monod (1944) has shown that in suitable concentrations the metabolic inhibitor 2,4-dinitrophenol (DNP) prevents formation of both constitutive and adaptive enzymes in Escherichia coli while permitting the enzymes already present to function. Growth is inhibited and respiration continues at a constant rate. These properties of the inhibitor have been confirmed with the strain of E. coli B used for these studies. If DNP is added to a culture, the rate of oxygen uptake will be constant and will represent the respiratory enzyme activity at the moment when DNP was added. This is very useful for experiments on adaptive enzymes. However, during experiments on adaptive enzymes in cultures infected with bacteriophage T2r+ it was found that when DNP was added the respiratory activity decreased and lysis of the infected cultures was accelerated (Heagy, 1949). The effects of inhibition by DNP and infection with phage T2r+ on cultures of E. coli B will be described in this paper. MATERLkLS AND METHODS Bacteria. Stock cultures of Escherichia coli, strain B, are maintained on agar slopes at refrigerator temperature and subcultured monthly. For experiments the fluid medium used was inoculated 1:100 from a 24-hour culture grown in the same medium. After 3 to 4 hours the culture was centrifuged for 10 minutes, the supernatant was discarded, and the cells were resuspended in fresh medium. After dilution to suitable turbidity, the washed suspension was added to the experimental tubes. Bacteriophage. With the exception of a few experiments with phage Ti, all the experiments were done with either phage T2r+ or phage T2r. The usual bacteriophage: bacteria ratio was about 3:1 to assure that most of the bacteria would be infected.2 Synthetic medium. Medium S2 of Monod and Wollman (1947), of the following composition, was used: KH2PO4, 1.5 g; Na2HP04 12H20, 16.5 g; MgSO4 *7H20, 0.2 g; NH4Cl, 2.0 g; CaCl2, 0.01 g; FeSO4c7H20, 0.0005 g; redistilled water, 1,000 ml; pH, 7.5. Nutrient broth. Difco nutrient broth, dehydrated, 8 g per liter, pH 6.8.

A “loop” method for counting viable bacteria or bacteriophage is described. In this method standard wire loops are used to transfer definite volumes of cultures in two dilution tubes and to spread fluid from the final dilution on an agar plate. Instead of a number of tubes and pipettes that must be laboriously cleaned, plugged, and sterilized, the only requirements are two sterile tubes containing 20 ml. of saline and two wire loops. The loops are sterilized by flaming.

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