Definition of "vitiation"

[…] air was universally reputed to be a simple or elementary body. It was liable, according to the phlogistians, to vitiation, by the addition to it of phlogiston […] being more or less phlogisticated, according to the degree of its power to support respiration and combustion.

1810, George Wilson, M.D., F.R.D.E. Ch. II. General Sketch of Cavendish's Scientific Researches and Discoveries, in The Life of the Honble Henry Cavendish, p. 39.

Lincoln once reprimanded a young army officer for indulging in a violent controversy with an associate. "No man who is resolved to make the most of himself," said Lincoln, "can spare time for personal contention. Still less can he afford to take the consequences, including the vitiation of his temper and the loss of self-control.

1936, Dale Carnegie, “Part 3, Chapter 1. You Can't Win an Argument”, in How to Win Friends and Influence People‎, page 137