to resist flexion of the joints, the muscles of the lower jaw and neck being generally first involved, those of the lower extremity last. It might possibly be confounded with stiffening from extreme cold or spasms; but frozen limbs yield a creaking noise when forcibly flexed, from breakage of the congealed moisture, and spasmodic contraction resumes its morbid position on removal of the correcting force. Not so post-mortem rigidity.
Putrefaction succeeds rigidity as a bluish-green tint of skin, commencing usually on the lower part of the abdomen and spreading over the body. Similar gangrenous appearances may occur during life, but, besides their more circumscribed extent, the invariable presence of a line of displaceable redness at the confines of the living tissues is a constant and characteristic distinction.
The desideratum, however, is some infallible proof of death whereby this state can at once be decided without waiting for the more tardy supervention of these positively post-mortem phenomena.
Neither the cadaveric aspect nor coldness and lividity of surface are constant or unequivocal signs. The cessation of the heart's action beyond five minutes is undoubted evidence, but it is impossible to acoustically determine this with absolute certainty, even when aided by the stethoscope, as the sense of hearing may be fallacious in delicate cases. Neither is the imperceptibility of the respiratory movements of the chest perfectly decisive. Conclusions from experiments on the eyes, by trying to excite the pupillary muscles by physiological agents, or by examining the fundus with the ophthalmoscope so as to observe certain changes supposed to be essentially post-mortem, are invalidated by the comparative unimportance of these organs to general vitality. The same uncertainty holds as to the effects produced by tightly ligaturing a limb, as there might be complete occlusion of its vessels and consequent arrest of its circulation without necessarily fatal results. The changes induced in a polished needle inserted deeply into the living tissues may be closely simulated by non-vital causes. Circumstances might also obscure the difference between the contents of vital and post-mortem vesication.
The possibility of absolutely deciding, in doubtful cases, as to the presence or absence of vitality depends on the possession of artificial means wherewith to sensibly demonstrate the minimum activity of each of the essentially vital processes, the utter negation of the various specific reactions under their appropriate tests being infallible evidence of death. The different available measures vary in their degree of simplicity and facility of application, but the results are all equally conclusive.
The validity of the respiratory test results from the fact that even during the most reduced state of vitality carbonic acid is perpetually generated in the system, and extricated therefrom through specially adapted air-passages, where its escape can invariably be detected by proper appliances.
