Decomposition and metamorphosis of animal beings--Influence they exercise over the soil as a habitation for man--Disposal of the excreta and remains of animals and vegetables--Danger of these when accumulated--Immunity of savage tribes--Scurvy amongst the white troops at the Cape of Good Hope, the healthiest climate in the world--Metamorphoses of organic remains--Influence of oxygen, of nitrogen, and ammonia--Source of the inorganic principles--Fluate of lime in fossil bones--Danger to man of putrescent sea-water--Man’s incessant struggle with nature--Fatality of the climate of Rio pp. 55–65 CHAPTER VIII. Earth, air, and water, in relation to man--How modified by him--Results of that modification--Action and reaction--Antagonism of man to nature--Effects of human labour on the soil--How man protects his dwelling--Distinction between a drain and a sewer, a distinction first practically denied in England--Chemical elements of animal bodies--Nourishment of plants--Exhaustion of the soil in Virginia--Value of farm-yard manure--Agriculture in China--Effects of clearing the primæval forests of America--Causes of the hay-fever, typhus and typhoid fevers--Effects of bad ventilation--Importance of the infusoria in nature’s great scheme--Origin and action of _humus_--Functions of the _humus_ and of the leaves--Means adopted in Holland for the conversion of a bog or morass into a polder--Antediluvian vegetation--Elements which require being restored to the soil--Belgian agriculturists--Statistics of Quetelet pp. 66–88 CHAPTER IX. On poisons, miasms, and contagions--Difficulties besetting the questions as to their essential nature and origin--Poison of typhus, of yellow fever, and of the remittent fevers of hot countries--Their appearance at uncertain and distant periods in an aggravated form--Statistics of the recurrence of remittents in the West Indies--Light thrown by chemistry on the subject--Fermentation and putrefaction--Peculiar poisons--Distinction between a miasm and a contagion--Odour perceptible in sick chambers--Ozone, pp. 89–98 CHAPTER X. On the servitude of rivers--Practical knowledge of the ancients--Early Roman history a fable--The great social problems of _race_ and _climate_ in some measure unknown to the Romans--First mooted in the reign of Justinian--Present phases of human society--How affected by these two problems--Influence of civilization over the earth pp. 99–110 CONCLUDING CHAPTER.