(5) =Effluvia from Decomposing Organic Matter.=—(_a_) =The air of marshes= contains an excess of carbonic acid, marsh gas, etc., in addition to other organic matters. Malarial diseases are commonly ascribed to the inhalation of the marsh effluvia under certain conditions, though the recent proof of the part played by the mosquito in spreading malaria, puts the inhalation of such effluvia in the background as cause of this disease (page 307). Some forms of diarrhœa and dysentery have been ascribed, with a less degree of probability, to the same cause. In this case, as in that of emanations from other organic sources, the impurities received by the air are both gaseous and particulate. (_b_) =The Air of Graveyards= contains an excess of carbonic acid. The older intramural graveyards appear to have been a cause of illness; but modern graveyards, kept under good regulations have never been shown to cause illness. (_c_) =The Effluvia from Decomposing Carcases=, especially of horses on the battle-field, have led to outbreaks of diarrhœa and dysentery among the soldiers. (_d_) =The Effluvia from Manure and Similar Manufactories= do not seem to injure the workmen as a rule, but attacks of diarrhœa have been produced in the neighbourhood when the wind has wafted the effluvia towards any particular part. Sore throat, and occasionally diphtheria, have been ascribed to the inhalation of London manure taken into Essex. (6) =The Effluvia from Certain Manufacturing Processes= seem to be rather nuisances than actually productive of ill health. The vapours given off by _tallow-making_ and _bone-burning_ processes are most disagreeable, but there is little or no positive evidence of their direct insalubrity. The air of _brickfields_ and cement works is peculiarly disagreeable. =The Degree of Moisture and the Temperature= of air are of great importance in relation to health. Air which is unduly moist or dry, hot or cold, may be injurious apart from any foreign matters it contains. The _relative amount of moisture_ is of greater importance than its actual amount. An atmosphere which contains aqueous vapour up to the point of saturation is very oppressive; the normal evaporation of insensible perspiration (and with it of the organic impurities removed from the skin) is interfered with; and consequently the “oppressiveness of the day” is complained of. _An unduly hot air_ is generally productive of pallor and ill health, though it is difficult to know how much to ascribe to the high temperature, and how much to the commonly coexistent vitiated atmosphere. The temperature of living-rooms ought not to be over 60° to 65° Fahr., and of bedrooms not over 60° Fahr.