_Internal Conditions._--1. Age; 2. Sex; 3. Condition of the body--(_a_) _Constitutional peculiarity_; (_b_) State of the body. 4. Kind of death--(_a_) _The result of disease_; (_b_) _The result of poisons_. External Conditions Which Modify Putrefaction 1. _Micro-organisms._--A fauna and flora of decomposition has been described in a paper by Hough on “The Fauna of Dead Bodies,” _B. M. J._, vol. ii. 1897, p. 1853, to which the reader is referred. Many different forms of micro-organisms combine in the production of putrefaction, and the result of their action is inevitable, unless the body be guarded against their invasion by special means, or the tissues be rendered unfit for their use. 2. _Air._--Exposure in the open air has a marked effect in promoting putrefaction; but garments fitting close to the body, and thus excluding air, have a contrary effect. Dry air, or air in motion, by assisting evaporation from the corpse, acts as a preservative. The composition of the soil in which the body is placed has also a more or less modifying effect. In light, porous soil, allowing of the free ingress of air, decomposition is more rapid than in close, compact soil, as clay; but in this we have to contend with another agent--moisture--which more or less counteracts the protective virtue of the closer earth. 3. _Moisture._--Putrefaction cannot proceed without moisture. The body, however, contains sufficient water to enable this process to commence spontaneously. Organic substances artificially deprived of water do not putrefy. Cold and heat possess marked antiseptic properties--the former by freezing the fluids in the body, the latter by drying them up. 4. _Warmth._--A temperature between 70° and 100° F. is found most favourable to decomposition. The effect of cold is shown by the fact that a body immersed in water during winter, at a temperature between 36° and 45° F., may be so well preserved as to present, ten or twelve days after death, well-marked signs of violence, which would in summer have been utterly obliterated in five or seven days. The preservative influence of cold water will, however, depend greatly on the depth at which the body has been submerged. Bodies so submerged, and then exposed to the air, putrefy with such rapidity that exposure for one day is said to work a greater change than three or four days longer retention of the body in the water. As an instance of the preservative power of cold, may be mentioned the mammoth found in Siberia embedded in a block of ice. Internal Conditions Which Modify Putrefaction 1. _Age._--The bodies of young children, other things being equal, are said to putrefy rapidly. It should be remembered, however, that clothing possesses considerable power in retarding putrefaction, and that, in the hurry and anxiety to get rid of the infants, they are oftener exposed naked than clothed, which may, in some measure, account for their more rapid decomposition.