A unique nicotinic acid degradation was devised which permitted the isolation of each individual carbon atom of the pyridine ring. Aspartate-3J4C and malate-3J4C were administered to Nicofzi~na rustica tobacco plants for 4 hours and found to be incorporated almost exclusively into carbons 2 and 3 of the pyridine ring of nicotine. When aspartate-3-l% was fed, 57% of the tracer resided at carbon ...

1. Titration of haem with pyridine in alkaline media of low ionic strength yields a true pyridine haemochromogen, compound III, at very low concentrations of pyridine. 2. Graphical analysis of this titration gives the first spectrophotometric evidence for a dimeric haem. 3. Compound III is unstable and tends to aggregate to a second compound, compound II, whose formation is enhanced under those...