PREFACE. THIS book has been prepared to meet the needs of students of medicine in the acquirement of a knowledge of those principles on which modern hygienic practices are based; to aid students in architecture in comprehending the sanitary requirements in ventilation, heating, water-supply, and sewage-disposal; and to aid physicians and health officers in familiarizing themselves with the advances made in hygienic practices in recent years. The rapid strides made in our knowledge of the entire subject of hygiene has rendered such a book, based upon the more recent discoveries, almost a necessity to students of medicine. No attempt has been made to treat the subject in an exhaustive manner, the object being merely to give the general principles upon which the health officer and the physician work in their respective capacities in dealing with conditions which are detrimental to health or which tend to improve health. The entire range of subjects comprising the comprehensive field of hygiene has not been discussed, but all those subjects which appeared to the author to be most. important for those for whom the book has been prepared have received the consideration which their relative importance demanded. The metric system of weights and measures has been employed throughout the work except in quotations, because this system is now in general use in all scientific laboratories in the United States, and because it is in every way preferable to the cumbersome and complicated system, with its various units, which is still in common use. The metric system was employed also because it is in common use on the Continent of Europe, and is also a legal system in the United States since 1866, when Congress passed an act making its use lawful in the construction of contracts and in all legal proceedings. It is rapidly coming into general use in medicine and pharmacy, and its general adoption has the hearty endorsement of numerous scientific societies. At the present time a bill is passing through Congress which, when enacted, will make its employment compulsory in all departments of the Government after January 1, 1903. In the Appendix the relative values of the units of weights and measures of the metric system have been given in terms of the English system, and vice versa. D. H. B. CONTENTS. Nature and Composition of the Atmosphere, 32.-Temperature of the Air, 34.-Pressure of the Atmosphere, 35.-Distribution of At- mospheric Pressure, 37.-Humidity of the Atmosphere, 38.- Hygrometry, 39.-Elastic Force of Vapor, 41.-Absolute Humidity, 41.-Relative Humidity, 41.-The Influence of Humidity on Health, 42.—Movements of the Atmosphere, 42.—Clouds, 43.—Precipitation of Moisture, 43.—Climate, 44.—Ground-air, 51.-Sewer-air, 52.— The Impurities in the Air, 52.-Examination of the Air by the Senses, PAGE Amount of Fresh Air Required, 66.-Cubic Space, 68.-General Rules for Ventilation, 70.-Natural Ventilation, 70.-Arrangements in Natural Ventilation, 72.-Artificial Ventilation, 80.-Removal of Loss of Heat from Buildings, 88.-Degree of Warmth, 88.-Heat Supplied by Radiating Surfaces, 89.-Systems of Heating, 91.- Drinking-water Required Daily, 112.-Source of Water-supplies, 113. Storage of Water, 117.-Purification of Water, 118.-Methods of Purification, 118.-Sterilization of Water by Means of Chemicals, 134. Suitability of Water for Boiling Purposes, 136.—Standard THE REMOVAL AND DISPOSAL OF SEWAGE..... The Removal of Sewage, 149.-Water-closets, 149.-Traps, 152. -Disposal of Sewage, 156.-Chemical Treatment of Sewage, 158. -Modern Methods of Sewage Purification, 160.-Sprinkling Filters, PAGE Chemical Composition of the Body, 176.-Potential Energy in Food, 178.-Energy Derivable from Food, 180.-Nutritive Value and Cost of Food, 186.-Digestibility of Foods, 188.-Composition of Foods, 190.-Functions of the Alimentary Principles of Food, 191.-Water as Food, 192.-Different Varieties of Food, 193.— Animal Foods: Meat, 193.-Food-poisoning, 197.—Composition of Meat, 203.-Fish, 205.-Milk and Milk-products, 205.-Vegetable Foods, 217.-Bread, 219.-Preserved Meats, 220.-Preserved Vege- table Foods, 220.-Food-preservatives, 222.-Nuts and Their Uses as Food, 222.-Mineral Food, 223.-Beverages and Condiments, 223.—Adulterations of Food, 225.-Dietaries, 228.-Nutritional |