We studied the effects of ammonia treatment on microbial populations during the fermentation of corn silage. We also compared the effects of ammonia to a preservative containing buffered propionic acid and other antifungal compounds on the fermentation and aerobic stability of corn silage. In the first experiment, whole-plant corn was ensiled without treatment or treated with ammonia-N to supply an additional 0.3% N (fresh-forage basis). The addition of ammonia immediately increased silage pH and had no effect on numbers of lactic acid bacteria, but delayed their growth compared with untreated silage. Numbers of enterobacteria declined more slowly, but numbers of yeasts and molds declined more quickly in silage treated with ammonia. During the early stages of ensiling, lactic acid increased more rapidly in untreated than in treated silage. The reverse was true for acetic acid concentrations. When exposed to air, growth of yeasts and molds was delayed in ammonia-treated silage. In a second experiment, various levels (0.1 to 0.3%, fresh weight) of ammonium-N or a preservative with buffered propionic acid were added to whole-plant corn and allowed to ensile for 106 d. Silage treated with ammonia had a greater ratio of L- to D-lactic acid than did other silages. Untreated silage was aerobically stable for 32.3 h, whereas the low (42 h) and moderate (52.7 h) concentrations of both additives numerically improved aerobic stability. High concentrations of ammonia-N (0.3%) or a buffered propionic acid preservative (0.3%), markedly improved the aerobic stability of corn silage (82 and 69 h for ammonia and propionic acid-treated silage, respectively).

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SUMMARY1. Cortical slices from kidneys of adult rats were equilibrated for 24 and 48 hr in the refrigerator in solutions containing 5 mM-K, 2-5 mm-Ca and Mg, m/15 phosphate buffer (pH 7.4), 5 mm cyanide and iodoacetate with 5, 6, 7 and 8 % polyethylene glycol (PEG 6000) and 77, 154, 308, 462 and 770 mM-NaCl.2. There were no consistent differences in water content between slices after 24 and after 48 hr.3. Slices contained more water when either the concentration of NaCl or that of PEG was reduced. The increase in water content induced by lowering the concentration of either was prevented by a higher concentration of the other.4. Water content was held constant at 3-25 kg. kg-' dry PEG-free tissue despite a fall in [NaCl] from 770 to 77 mm (more than 1200 m-osmole.kg-') by increasing PEG from 5*1 to 7.7 % corresponding to an increase of the order of 15 m-osmole. kg-'.5. It is suggested that PEG 6000 was so much more effective than NaCl, osmole for osmole, because PEG 6000 acted as a non-penetrating solute, whereas NaCl penetrated the slices and reduced the 'Donnan excess' component of the intracellular colloid osmotic pressure so that this could be balanced by a smaller concentration of PEG.

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