Prosy says death is really due to carbonic acid poisoning.
"Somehow Good"
William de Morgan
If, on the other hand, the circulation is bad, as in some forms of lung disease and heart disease, so that the blood is loaded with carbonic acid until it is blue and dark, then the lips may become purplish or dark blue, and the finger nails nearly the same color.
"A Handbook of Health"
Woods Hutchinson
Besides oxygen and nitrogen, there is also in the air a little carbonic acid and vapor.
"In Search of a Son"
William Shepard Walsh