Chicken eggs incubated under hatchery conditions for 19 days show significant decreases in the total content of water and organic nitrogen, but not of sodium or potassium. The hypothesis is discussed that the formation of gaseous nitrogen is responsible for the nitrogen loss.Metabolic production of elemental nitrogen by germfree mice and by man has been suggested by data obtained in our laboratory. We used a closed svstem that could be flushed practically free from preexisting N2 and in which atmospheric contamination was excluded with confidence (1-3). Attempts to further document the pathway using [15N]amino acids were unsuccessful mostly because of the technical difficulties involved.This problem, which has obvious implications vis-a-vis nutritional concepts on one side, and gas exchange theory and measurement on the other, has received recent attention from respiratory physiologists, who have reinvestigated the Lavoisier-Haldane postulate of equality between inspiratory and expiratory N2 (4-10). The most careful of these experiments (9) have found an excess of expiratory N2 of the order of 0.59-4.4 ml/min; this is a quantity nearly identical to the one reported by us with a totally different technique (3). Such amounts of N2 are sufficiently small to be negligible in the usual respiratory calculations, although not negligible from a metabolic standpoint. The volumes involved approach the limit of the sensitivity of the respiratory balance method; therefore, the authors could not decide whether the excess expiratory N2 represented metabolic production or persistent nitrogen washout.Clearly, definitive answers, obtained through a multitude of approaches, to this important problem are needed.The avian egg represents an actively metabolizing and differentiating system permeable to gases or vapors (11,12). It thus provides a technically simple model and a new approach. We have measured total "Kjeldahl" § nitrogen in groups of fertilized chicken eggs before incubation and 2 days before hatching, and have demonstrated significant nitrogen loss, associated with growth and maturation of the embryo. § The meaning of the term "Kjeldahl" nitrogen is well known and indicates the nitrogen measurable with the Kjeldahl method, i.e., that in protein, amino acids, urea, ammonia, nucleic acids, uric acid, and the like. Inorganic nitrogen such as nitrates, N2, and nitrogen oxides are not measured by the Kjeldahl method (13).The hypothesis that the loss of "organic" nitrogen is due to formation of N2, which then diffuses out of the egg, is discussed. METHOD AND MATERIALSFertilized eggs from chickens (Gallus domesticus) were selected at the hatchery from those laid within the previous 24 hr.The eggs were then randomlyF allocated to two groups of at least 60 each, numbered, and weighed. The control group was frozen and analyzed at once. The other group was incubated for 19 days in the hatchery, under supervision of the hatchery personnel. On the morning of the nineteenth day, most of the incubated eggs were removed from th...
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