Alcohol and common salt both act in the preservation of bodies by their affinity for water. If a piece of flesh is covered with salt, the water gradually passes from the pores of the flesh, and dissolving the salt forms a brine, which does not wet the flesh, but trickles off its surface; the water necessary for putrefaction is thus removed. Fourth, by excluding oxygen, the putrefactive process is retarded, precisely as the fermentative action of the gluten in grape juice cannot begin until a certain quantity of oxygen be absorbed. It is thus that meat that is sealed up in close vessels and then boiled for a moment is preserved; the small quantity of oxygen of the air remaining then in the vessel is absorbed, and the produce of that minute change being coagulated by heat it cannot proceed farther. A high temperature stops putrefaction by coagulating the azotized materials; a temperature below 32° by freezing the water acts as if the tissues had been dried; in both cases putrefaction is arrested. During putrefaction, at a stage prior to any fetid gas being evolved, a peculiar organic substance is generated, _possessed of intensely poisonous properties, and the blood of persons who have died from its effects is found to be quite disorganized and irritating when applied to wounds_. This and the blood of over-driven cattle are found to produce effects similar to those of venomous reptiles, and the wounds received in dissection are sometimes followed by similar fatal consequences. The communication of disease in this way has recently been very ingeniously ascribed by Liebig to the general principle of the communication of decomposition by contact. The small quantity of diseased organic matter originally introduced into the system by absorption, acts as a ferment and reproduces itself in the mass of the blood, until this becomes unfitted for the performance of its functions and the animal is killed; the active principle being thus copiously present, is exuded from the skin and lungs and gives a contagious character to the disease, or it remains only in the blood, or is secreted in _pustules_, constituting infection, by which the disease may be communicated to some other person. This brief enumeration of the process of putrefaction will, to a certain extent, elucidate the process of embalming given in this book; it shows that the different methods herein explained, fulfill the conditions necessary to stop the progress of decomposition. A most important point, and one which ought not to be passed upon without serious consideration is, the communication of disease by contact and absorption.