From the great complexity of the composition of animal substances, their decomposition is more rapid and its products more diverse than in the case of organic bodies of vegetable origin. While the carbon, hydrogen and oxygen give origin to the various kinds of ulmine and other substances of the same class, the nitrogen is generally valued as ammonia, and the sulphur as sulphurated hydrogen. It is the presence of these bodies that give to the putrefying substances the disagreeable odors by which that process is distinguished from mere mouldering and rotting.
Even during life, the constituent particles of the body are in a continual state of change, being absorbed and thrown out of the system, while others are assimilated in their place. Any part of our constituents, liquid or solid, which become unfitted for this vital function, is thereby killed, and must, if not got rid of, induce the death of the individual.
Hence, precisely the same means which give to the animal substances the fixity of constitution which belongs to true chemical compounds, and thus preserve them from decomposition by the disturbing action of their own elements (as when we coagulate albumen by an acid, by corrosive sublimate, or by sulphate of copper), produce if applied to the living body the death of the part or the whole being by depriving the blood or the tissue of the mutability of constitution, which is required for the functions of the animal frame.
It is thus that the generality of metallic poisons act in producing death. Being absorbed into the system, they unite with the albumen and fibrine of the blood, and converting them into the insoluble compounds which we form in the laboratory, unfit them for the continual absorption and secretive offices, which, as organs, while they live they must fulfill. If the injury be local and limited in extent, the part so coagulated may be thrown off, and after a certain time the functions return to their proper order. If the mass, or the importance of the affected parts be greater, the system cannot so get rid of the portions which have thus been removed from the agency of life, to submit to merely chemical laws; on the contrary, the vital powers of the remaining portions of the animal are so much weakened in the effort that general death is caused.
For putrefaction it is thus necessary: 1st. That the force of vitality which governs so completely the mere chemical tendencies of the elements of our tissues be removed.
2d. That there shall not be present any powerful chemical reagent with which the organized material matter may enter into combination and thus the divellent tendencies of the affinities of its elements be overcome.
3d. That water be present in order to give the necessary mobility.
4th. That oxygen be present, or at least some other gas, into the space occupied by which the gaseous products may be diffused; and lastly, that the temperature shall be within moderate limits, putrefaction being impossible below 32° or above 182°.
The agency of the first of these preventive powers need not be further noticed. The second is extensively employed for embalming purposes, and in the preparation of bodies for anatomical studies, by baths, or injections into the arteries of solutions of corrosive sublimate, acetate of alumina, sulphate of iron, tannin, wood vinegar, and creasote; this last body, however, does not appear to act by direct combination, but by the complete (catalytic) coagulation it produces in all the tissues of the body that have protein for their base.