Abstract:
1. In vitro experiments have been conducted on the disappearance of
potassium nitrate in ruminal ingesta from sheep on different diets.
2. Nitrate disappears more rapidly from ingesta of lucerne-fed sheep
than from that of sheep on grass hay.
3. Nitrite is formed from the nitrate. It appears very soon after the
addition of nitrate to the ingesta, reaches its maximum concentration at the
moment of complete disappearance of the nitrate and subsequently itself
disappears. Nitrite thus formed represents an intermediate stage in the
conversion of nitrate to more fully reduced compounds.
4. The ratio nitrite disappearance time / nitrate disappearance time is
constant for varying quantities of nitrate (Constant A).
5. The nitrite formed also disappears more rapidly from ingesta of
lucerne-fed sheep than from that of sheep on grass hay.
6. The disappearance of nitrate from ingesta is represented graphically
by plotting quantity of nitrate against time of disappearance. The resulting
curve is a half parabola, with values varying for different ingesta. Daily
variation for ingesta can be plotted from a series of such curves.
7. Nitrate disappearance rate can be used as an additional measure of
ruminal activity.
8. The addition of glucose shortens the time of nitrate disappearance;
the maximum effect for a fixed quantity of nitrate is produced by as little
as 15 to 30 mg. of glucose per 20 c.c. of ingesta.
9. The "nitrate disappearance curve" is shifted in position, but
remains unaltered in relative proportions, by the addition of a fixed quantity
of glucose to the tube in each reading. The percentage reduction of time
of disappearance of different quantities of nitrate due to a fixed quantity of
glucose is a constant (Constant B).
10. The time of disappearance of nitrite formed from the nitrate is
similarly affected by the presence of glucose. The percentage reduction of
nitrite disappearance time due to a fixed quantity of glucose is also constant
(Constant C).
11. "Nitrite persistence" is defined as the interval of time between
the disappearance of nitrate and of nitrite. The percentage reduction of
nitrite persistence due to a fixed quantity of glucose constitutes a fourth
constant (Constant D).
12. An in vivo experiment confirmed the in vitro findings on the effects
of nitrate, supplied either alone or in conjunction with sugar, on the
ruminal ingesta of sheep. It demonstrated clearly the effect of diet and of
sugar on nitrate persistence and therefore on nitrite poisoning.
13. Further work on this subject, both from the toxicological and the
nutritional aspects, is in progress.
