Author’s theory of malaria--Has malaria a real existence?--Action of ferments on the blood--A malarious air not dislodged by storms--Quality of the air over ditches, &c.--Experiments by the Author on microscopic mollusca--Influence of chemistry over physiology--Ammonia--Its volatility and universal prevalence in the air--Its sources and action on living bodies--Danger of drainage-works during summer--Spread of plants through the air--Appearance of strange plants in a country--Conclusion--Various phases of sanitary science--laws of decomposition and composition--Results to man of a false position in nature pp. 111–128 APPENDIX pp. 129–136 ERRATUM. Page 98, line 2 (note), _should read_ “Hydrogen is the lightest known substance; its specific gravity is to that of air 732 to 10,000.” AN INQUIRY INTO THE ORIGIN AND INTIMATE NATURE OF MALARIA. INTRODUCTION. In addition to the wide-spread desolating epidemics which appear from time to time, mysterious in their origin, progress, and cessation or disappearance--such, for example, as the plague of Athens, the plague of London in the time of Charles the Second of happy memory, the Indian or Asiatic cholera of modern times, and the disease called influenza, a frequent visitor to Western Europe during the last half-century--there exist localities unceasingly under the influence of a poison inimical to human life. This poison, since it may be so called, is known to haunt the deltas of large rivers, and seems to be always present there; but it is found also, if we may determine its identity by the identity of its deleterious influence on men, in other and very various localities: sometimes it shows itself--and this most commonly--in marshy and fenny countries, where no large rivers exist, at other times by the banks of fresh-water lakes; now it haunts the forest, and now the open plain, where marsh and fen, swamp and decaying vegetation, seem all but absent. As the inhabitants of such localities are especially afflicted with the fevers called intermittent and remittent, it is the most natural thing in the world to ascribe to the locality itself the origin of these diseases. When, however, we attempt to generalize and assign to the same cause in a more concentrated form those terrible fevers which render tropical countries the graves of Europeans, great difficulties arise, and numerous objections, which the best of statisticians, not to mention the simply medical observer, have failed to elucidate and remove. Thus physicians are not agreed as to the identity of the poison under all circumstances, or in other words, demonstrative evidence is still wanting to prove that the cause of fever on the western coasts of Africa is identical with that which has so often in the Antilles destroyed England’s chosen troops, decimated