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Measurements of nitrate concentration and relative enrichment in nitrogen-15 were made on samples of the surface waters of a typical Illinois corn belt watershed and the effluent of the subterranean tiles that drain the cropped land in the region. From these measurements, we estimate that at the time of peak nitrate concentration in the spring of 1970 a minimum of 55 to 60 percent of the nitrogen found as nitrate in the surface waters of this watershed originated from fertilizer nitrogen

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BIOCHEMISTRY: COMMONER ET AL. organisms suggests that the system yielding acetate from pyruvate may be involved in the mechanism controlling the balance between prophage and host. We could find no effect by the addition of lipoic acid, or any other of the adjuvants, on systems of virulent phase infection-by T1-of either lysogenic or nonlysogenic organisms as measured by efficiency of infection, survivors, and burst size, in onestep growth experiments.6 This finding was not unexpected. In a system of an organism invaded by a virulent phage the host must cope not only with the invading DNA but with the toxic protein moiety as well. An induced lysogenic organism where there is no foreign protein involved could thus be expected to be more amenable to restoration during the early phase after induction. However, it may be relevant that Spizizen7 has shown that E. coli grown on lactate or L-serine accumulates pyruvate after infection by phage T2 or T7, indicating that some alteration of pyruvate metabolism may be a concomitance of infection by virulent phage as well.