Thanks to the always-fascinating book by Jan Bondeson, Buried Alive, the Terrifying History of our Most Primal Fear (W.W. Norton, 2001), which excited this interest in Dr. Severin Icard.
The determination of the occurrence of death was a major medical feature of the 19th century, the French in particular waging a fight for how this to be so. Briefly put, for centuries even before Pliny death was described as the absence of an audible heart—the crux of the sentence being the word “audible”, so that the end of life was dependent upon being a physician’s/person’s capacity to hear the heart beating. This might be very problematic if the person listening for that heartbeat had faulty hearing from defect or age, as the listener would place his/her ear on the chest of the patient to determine if the heart was functioning or not. The stethoscope wasn’t invented until 1816 by Rene Laennec--who produced a monaural device much like a primitive hearing horn made of solid wood—which was a vast improvement over no stethoscope at all, by again was very crude compared to early 20th century devices. It was much more preferred by most doctors (though there were contingents who distrusted the instrument and wouldn’t use it and still others who thought it an insult to their person insinuating defective hearing capacity) compared to the ancient hairy-ear-on-chest method. It was also, in a small way, a kind of auditory x-ray.
There were other ways to make the sometimes very difficult determination of actual death. Some methods seem extreme, and a little barbaric, and at the very least, "odd", but they were also effective to some degree. For example, Leon Collongues believed that he could hear the capillary functions of a possibly-dead person’s fingers if placed in his ear; Jules Antoine Josat invented a nipple-pincher ("pince-mamelon") life-rejuvenation device, operating on the assumption that a deeply sedated person could not resist a strong pinch of the nipple and would have to wake up if alive; the tongue-pulling idea of Dr. J.-V. Laborde; Christian August Struwe’s electrical device that delivered a dual shock to the eye and lip that was supposed to result in a twitch in the supposed-departed's eye or lip; the tobacco enema of Antoine Louis; Barnett's scalding death cure, which recommended burning the skin of the arm to see if it blistered (no blister/no life); and so on, deep into the fearsome, troubled and death-filled night.
There was one death test, though, that went beyond the others, if only because it employed a "written test". This was the invention of Dr. Severin Icard, who devised a putrefaction test where the words "I am really dead" on a piece of paper written in acetate of lead would be placed under the note of the "deceased" where the words would appear if they came into contact with putrefaction gas dioxide of sulphur. So, the "breath" of the dead would force the letters to announce their death. Unfortunately the test was not fool-proof and the not-dead could sometimes produce dead results, which would be highly unfortunate in the premature burial kind of way...which is somewhat ironic, because that is how many of these dead tests came into being.
I should point out that Icard had another outre idea for the physical determination and identification of criminals. He proposed that a substance be injected into an unidentified part of a felon to identify the person as a criminal. the injection would produce a visible bump or lump on the person, somewhere; multiples were also possible, as were the locations of the bumps, so that a trained eye could determine the crimes committed by the Bump Map of Crime on the victim.[Source: Journal of the American Medical Association, volume LVII, July-December 1911.]