A manual of practical hygiene for students, physicians and medical officers

Front matter

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Preface To The Second Edition

The demand for a second edition of this work within but little more than a year from the appearance of the first is gratifying evidence that the book in some degree has filled a requirement. During the interval, research in the field of hygiene has been active and fruitful, and the results have been incorporated in great measure in the present issue. A chapter on the relatiim of insects to human diseases, containing eight additional illustrations, has been added, parts of other chapters have been entirely rewritten, and throughout the book numerous changes and additions have been made. The amount of new material occupies about seventy pages, but the size of the book has been kept within reasonable limits by the excision of about thirty pages dealing chiefly with quarantine law and obsolete matter.

The author entertains the hope that the second edition will be no less cordially received than the first.

C. H.

6SS BoYLSTON Street, Boston, August, 1902.

Preface To The First Edition

In preparing this work, the object of the author has been to provide a students' text-book which should ex)ver the most important topics included in the wide domain of Hygiene, and be useful in the laboratory and as a reference book for practitioners and health officers.

The subject is so broad that it is impossible to treat it in its entirety in a thorough manner in a single volume; therefore, certain topics which find a place in some of the larger works, and which are of interest chiefly to a somewhat limited circle of specialists, have not been considered.

Of late, it has become the custom to incorporate in works on hygiene a chapter on elementary bacteriology. It has seemed to the author that, inasmuch as a knowledge of this closely allied science is recognized as a very essential part of the equipment of the modern medical practitioner, and is taught, as its importance deserves, either as a separate subject or in connection with pathology, it would be as much a work of supererogation to give a brief description of species and technic herein as to include a chapter on elementary chemistrj', physics, or other affiliated great subject. It is assumed that the reader has already acquired at least a fair working knowledge of bacteriology, or that, lacking it, he will turn rather to special works in which the science is fully treated.

Again, certain topics, which not infrequently are included in works of this nature, but which lie more properly within the fields of engineering and architecture, such, for example, as the construcjtion of aqueducts and sewers, the nature and strength of building materials, and the arrangement of hospitals, have been deemed as hardly within the province of the hygienist, and, consequently, have been excluded.

To those who, by their writings and otherwise, have been of assistance in the preparation of this book, the author extends his sincere thanks ; and especially to his friend and colleague Professor Harold C. Ernst for taking the photomicrographs from which the plates illustrative of the starches and trichinse have been prepared.

C. H. 688 BoYiJBTON Stbeet, Boston.

Chapter I. Page

§ 1. General Gonsidebations « 17

The nutritive value of foods, 17. Amount of food necessary, 18. Composition of foods, 19. Proteids, 19. Fats, 21. Carbohydrates, 21. Organic acids, 22. Inorganic salts, 23.

§ 2. Animai. Foods : Meats, Fish, Eggs, and Meat Products 23

Meats, 24. Digestibility, 24. Flavor, 24. Texture, 26. Effects of cooking,

25. Characteristics of good meat, 26. Comparative digestibility of meats,

26. Red meat and white meat, 27. Composition of meats, 27. Beef, 28. Pork, 29. Veal, 30. Mutton, 30. Lamb, 30. Poultry, 31. Horse meat, 31. Meat preparations, 32. Sausages, 32. Fish, 34. Digestibility, 35. Keeping qualities, 35. Composition, 35. Meat and fish, and pai-asitic disease, 37. Transmission of disease by meat and fish, 42. Tuberculosis, 43. Typhoid fever and cholera, 48. Poisoning by meat and fish, 53. Poisoning due to substances normally present in the living organism, 53. Poisoning due to bacterial products in meats and fish, 53. Onset and course of symptoms, 57. Nature of symptoms, 57. Postrmortem appearances, 58. Character of meats which cause poisoning, 58. Cases illustrative of poisoning by fish and meats, 60. Poisoning by mussels, 60. Poisoning by herrings, 61. Poisoning by salmon, 63. Poisoning by oysters, 63. Poisoning by veal, 64. Poisoning by pork, 66. Poisoning by beef, 70. Poisoning by horse meat, 73. Poisoning by sausages, 74. Poisoning by kid meat, 76. Meat inspection and slaughtering, 76. E^ 78. Lard, 81.

§ 3. Milk and Milk Products 82

Composition of cows* milk, 82. Fat, 83. Milk sugar, 84. Proteids, 84. Mineral matter, 85. Specific gravity, 85. Reaction, 85. Appearance, 85. Taste, 86. Presence of alcohol, 86. Colostrum, 87. Changes produced in milk by boiling, 87. Changes due to bacterial action, 88. Preservation of milk, 91. Adulteration of milk, 94. Condensed milk, 95. Koumiss and kefir, 95. Cream, 96. Milk as a factor in the spread of disease, 96. Poisonous milk, 96. Milk from diseased cows, 98. Milk contaminated from without with oi-ganisms related to human diseases, 104. Diphtheria, 105. Cholera, 105. Scarlet fever, 106. Typhoid fever, 107. Cholera infantum, 108. Analysis of milk, 110. Determination of specific gravity, 111. Determination of fat, 112. Determination of total solids, 115. Determination of milk sugar, 116. Determination of ash, 117. Determination of proteids, 117. Detection of added coloring matters, 118. Detection of preserva-

PAGE

tives, 120. Methods of distinguishing between raw and cooked milk, 122. Detection of gelatin in cream, 123. Butter, 124. Butter aa a carrier of disease, 127. Analysis of butter, 128. Clieese, 132. Composition of cheese, 134. Adulteration of cheese, 135. Analysis of cheese, 135. Cheese as a cause of poisoning, 136.

§ 4. Vegetable Foods 136

Farinaceous seeds, 137. Cereals, 137. Wheat, 137. Composition of wheat, 138. Wheat flour, 139. Preparations of wheat flour, bread, 140. Macaroni, spaghetti, and vermicelli, 142. Adulteration of flour, 143. Rye, 144. Barley, 144. Oat8,.145. Com, 146. Rice, 147. Buckwheat, 148. Legumes, 148. Peas, 149. Beans, 150. Lentils, 151. Farinaceous preparations, 151. Sago, 151. Tapioca, 151. Arrowroot, 152. Fatty seeds (Nuts), 152. Almonds, 152. Cocoanuts, 152. W^alnuts, 152. Peanuts, 153. Chestnuts, 153. Vegetable fats, 154. Olive oil, 154. Cotton-seed oil, 154. Tubers and roots, 154. Potatoes, 154. Sweet potatoes, 157. Artichokes, 157. Roots, 157. Herbaceous articles, 158. Fruit pix)duct8 used as vegetables, 158. Fruits, 159. Apples, 159. Pears, 160. Peaches, 160. Apricots, 160. Plums, 160. Cherries, 160. Oranges, 160. Grapes, 161. Melons, 161. Bananas, 162. Figs, 162. Berries, 162. Edible fungi, 163. Mushrooms, 163. Trufiies, 163. Saccharine preparations, 163. Cane sugar, 163. Maple sugai*, 164. Glucose, dextrose, 164. Molasses, 165. Honey, 165. Confeotionery, 167. Jellies and jams, 168.

§ 5. Beverages 168

Stimulant beverages containing alkaloids, 168. Tea, 168. Adulteration of tea, 170. Coffee, 171. Cocoa, 173. Fermented alcoholic beverages, 175. Beer, 175. Process of manufacture of beer, 177. Substitutes for barley malt, 178. Substitutes for hops, 179. Physical properties and chemical composition of beer, 180. Adulteration of beer, 180. Analysis of beer, 181. Tables showing percentage of alcohol by weight and by volume, 182. Detection of preservatives, 188. Wines, 189. Classification of wines, 191. Composition of wines, 191. Adulteration of wines, 192. Analysis of wines, 194. Detection of preservatives, 195. Cider, 196. Perry, 197. Distilled alcoholic beverages, 197. Brandy, 198. Whiskey, 199. Rum, 200. Gin, 201. Liqueurs, 201.

§ 6. Condiments, Spices, and Bakers* Chemicals 202

Vinegar, 202. Lemon juice and lime juice, 204. Salt, 204. Mustard, 205. Pepper, • 205: Cloves, ' 205. Cinnamon and cassia, 206. Allspice, 206. Ginger, 206. Nutmeg, 206. Mace, 206. Cayenne pepper, 206. Baking powders, 206.

Cold, 209. Drying, 209. Salting, 209. Smoking, 209. Canning, 209. Chemical treatment, 211. Boric acid and borax, 213. Salicylic acid, 216. Sulphites, 217. Formaldehyde, 217. Hydrogen peroxide, 218. Sodium fluoride, 219. Sodium bicarbonate, 219.

§ 8. Contamination op Foods by Metals 219

Copper, 219. Lead, 221. Zinc, 222. Nickel, 222. Tin, 222. Metallic contamination from kitchen utensils, 222.

Chapter II. Paob

AIB 224

Oxygen, 224. Nitit>gen, 226. Argon, 227. Hydrogen, 227. Carbon dioxide, 227. Ozone, 229. Peroxide of hydrogen, 230. Ammonia, 230. Nitrogen acids, 230. Aqueous vapor, 231. Dust and micro-organisms, 233. Oarbon monoxide, 235. " Sewer gas," 237. Organic matters, 240. Efiects of vitiated air, 240. The air as a carrier of infection, 244. Influence of fog, 261. Examination of air, 251. Determination of aqueous vapor, 252. Determination of relative humidity, 253. Glaisher's table, 254. Table of tensions, 255. Determination of carbon dioxide, 257. Determination of carbon monoxide, 265. Determination of ozone, 266. Determination of dust, 267. Bacteriological examination, 268.

Chapter III

The soil, 270. Constituents of the soil, 272. Physical properties of soils, 273. Pore-volume, 273. Permeability of soils, 274. Capacity for water, and water-retaining capacity, 278. Soil temperature, 280. Changes in the chai^ acter of soils due to chemical and biological agencies, 282. Soil-air, 283. Soil-water, 286. Sources of soil-water, 289. Loss of soil moisture by evaporation, 289. Influence of vegetation on soil moisture, 290. Other efiects of vegetation upon the soil, 291. Pollution of the soil, 292. Bacteria of the soil, 294 Soil anddiseaise, 296. Soil dampness and disease in general, 296. Soil and pulmonary tuberculosis, 297. Typhoid fever, 297. Cholera, 300. Bubonic plague, 300. Diphtheria, 301. Malaria, 302. Tetanus and malignant cedema, 303. Anthrax, 304. Epidemic diarrhoea, 305. Goitre, 306. Yellow fever, 306. Other diseases, 306. Examination of soils, 307. Poi-e-volume, 308. Permeability to air, 309. Permeability to water, 310. Water capacity, 312. Capillarity, 312. Moisture, 312. Organic and volatile matters, 313. Determination of C0| in soil-air, 313. Bacteriological examination of soil, 315.

Chapter IV

Introductory, 316. Rain, 316. Surface-waters, 317. Ground-waters, 318. Physical and chemical characteristics of water, 320. Appearance, 321. Reaction, 322. Odor, 322. Substances found normally in water, 324. Gases, 324. Carbon dioxide, 325. Organic matter, 325. Ammonia, 326. Albuminoid ammonia, 328. Nitrites and nitrates, 328. Mineral matters, 330. Salt, 330. Hardness, 331. Bacteria in water, 332. Water supplies, 335. Stored rain, 335. Surface-waters, 337. Ground-waters, 338. Springs, 338. Wells, 339. Driven welLs, 340. Drainage area of wells, 344. Filter galleries, 346. Classification of waters from the sanitary standpoint, 347. Purification of water, 349. Oxidation, 349. Dilution, 350. Sedimentation, 350. Bacterial action, 350. Vegetation, 350. Methods of purification, 351. Chemical treatment, 351. Boiling and distillation, 355. Filtration, 355. Domestic filters, 355. Filtration of public supplies, 357. " Mechanical filtration," 363. Plaque filters, 363. Removal of hardness, 364. Removal of iron, 364. Action of water on lead and other metals, 365. Action on iron, 369. Action on zinc.

PAGE

369. Action on tin, 370. Water and disease, 371. Disorders connected with mineral matter, 372. Disorders connected with organic pollution, 374. Typhoid infection of water supplies, 376. Influence of introduction of public water supplies on typhoid rates, 377. Classification of cities according to typhoid fever death-rates, 379. Examples of typhoid fever epidemics and of limited outbreaks traced to infected water, 381. Asiatic cholera, 386. The propagation of cholera m India, 388. Parasites and drinking-water, 391. Ice, 393. Chemical examination of water, 394. Collection of samples, 394. Determination of free and albuminoid ammonia, 395. Determination of other nitrogen compounds, 400. Nitrites, 400. Nitrates, 401. Determination of chlorine, 402. Determination of residue, 403. Determination of hardness, 403. Determination of "Oxygen required," 404. Determination of color, 406. Determination of odor, 406. Determination of reaction, 406. Determination of turbidity, 406. Detection and determination of lead, 406. Detection of tin, 409. Detection and determination of iron, 409. Inferences as to character of water from the results of sanitary chemical analysis, 409. Bacteriological examination of water, 412. Collection of samples, 413. Planting of samples, 413. Quantitative determination, 414. Qualitative determination, 416. Comparative value of chemical and bacteriological analysis of water, 417.

Chapter V

1 1. Genebai. Considebations 420.

Aspect, 420. Construction and arrangement, 420. Care of habitations, 421. Schools, 421. School furniture, 422. Legislation concerning schools, 423.

§ 2. Venttlation and Heating 423

Ventilation and heating, 423. Amount of space required for good ventilation, 425. Natural forces in ventilation, 426. Diffusion and gravity, 427. Periflation and aspiration, 429. Natural ventilation, 431. Inlets and outlets, 432. Mechanical ventilation, 435. Artificial heating in its relation to ventilation, 435. Badiation, 436. Conduction, 436. Convection, 436. Methods of warming, 437. Open fires, 437. Stoves, 437. Furnaces, 439. Hotrwater pipes, 439. Steam pipes, 439. Eegulation of temperature, 440. Necessity of providing moisture, 441. Determination of rates of ventilation, 443.

§ 3. Lighting 445

Natural lighting, 446. Artificial lighting, 447. Luminosity of flame, 447. Gas burners, 448. Varieties of illuminating gas, 449. Coal-gas, 449. Watei^ gas, 449. Acetylene gas, 460. Gasolene gas, 451. Impurities given off" in lighting, 451. Gas pipes, 461. Fixtures, 452. Electric lighting, 462.

Plumbing, 452. The soil-pipe and main drain, 464. Waste pipes, 459. Traps, 460. Grease traps, 464. Loss of seal, 466. Non-siphoning traps, 468. Water-closets, 470. The pan closet, 473. The plunger closet, 474. Hopper closets, 475. Open wash-out closets, 476. Siphon closets, 476. Flushing apparatus, 478. Water<iloset connections, 479. Urinals, 480. Wash basins, 480. Bathtubs, 482. Sinks, 484. Laundry tubs, 486. House service tanks, 485. Service pipes, 486. Testing plumbing, 487.

Chapter VI. Page

Sewage, 488. Methods of sewage disposal, 491. Discharge into the sea, 491. The pail system, 492. Chemical treatment, 493. Action of sewage effluents on fish life, 494. Sewage irrigation, 494. Influence of sewage irrigation on health, 498. The Waring system of irrigation, 499. Sewage filtration, 500. Other biological processes, 502. Dibdin's bacteria filter, 502. Cameron's septic tank, 504. The Scott-Moncrieff system, 505.

Chapter VII. Disposal Of Garbage 507

Garbage, 507. Methods of disposal of garbage, 508. Incineration, 508. Reduction, 509.

Chapter VIII

Disinfectants, 511. Physical agents, 511. Light, 511. Heat^ 514. Dry heat, 515. Steam, 515. Boiling water, 519. Cold, 519. Chemical agents, 520. Oxygen, 522. Ozone, 522. Hydrogen peroxide, 523. Chlorine, 524. "Chloride of lime,'' 524. Sodium hypochlorite, 526. Bromine and iodine, 526. Sulphur dioxide, 526. Lime, 527. Ferrous sulphate, 528. Ferric sulphate,

529. Ferric chloride, 529. Zinc chloride, 529. Aluminum chloride, 529. Potassium permanganate, 530. Copper sulphate, 530. Mercuric chloride,

530. Mineral acids, 532. Organic substances, 532. Carbolic acid, phenol, phenic acid, 532. Cresols, 534. Creolin, 535. Lysol, 536. Bacillol, 536. Lysoform, 536. Saprol, 536. Solveol, 536. Solutol, 537. Alcohol, 537. Essential oils, 538. Soaps, 538. Medicated soaps, 541. Formaldehyde, 542. Formaldehyde apparatus, 543. Germicidal properties, 549. Power of pen©, tration, 552. Conditions favoring action, 553. Toxicity, 554. Amount necessary for room disinfection, 556. Disadvantages, 556. Other applications of formaldehyde, 557. Prevention of dissemination of infectious material: Practical disinfection, 557. Disinfection of faeces, 558. Urine, 559. Sputum, 659. Discharges from the mouth, etc, 559. Eating utensils, 559. Bed linen and clothing, 559. Hands, 560. Air, 560. Room disinfection, 561. Disinfection of books, 564. Disinfection of waterKilosets, 564.

Chapter IX

Introductory, 665. The recruit, 567. Age, 568. Height, 671. Weight, 672. Examination of the recruit, 572. Chest capacity, 573. Grounds for rejection, 573. Hygiene of the soldier, 675. Personal cleanliness, 576. Contentment and cheerfulness, 575. Clothing of the soldier, 576. Wool, 576. Cotton and linen, 576. Shoddy, 576. Color, 577. Military dress coats, 577. Gaiters and l^^gings, 577. Head covering, 577. Stockings, 578. Boots, 578. Underclothing, 679. Abdominal bands, 579. Waterproof blankets, 580. The soldier^s exercise and work, 580. Marching, 580. Care of the feet on the march, 685. Care of other parts, 586. The soldier's food ; " rations," 587. Alcohol

PAQB

in the ration, 589. Preparation of food, 591. Is the U. S. ration adequate in amount and composition? 691. Is the U. S. ration suited to the tropics? 593. Tropical dietaries, 595. Posts and camps, 597. Barracks, 599. Tents, 601. Water supply, 604. Sewerage, 604. Sinks and latrines, 605. Inspections, 606. Sanitary police, 607. The diseases of the soldier, 613. Typhoid fever, 614. Dysentery, 615. Malaria, 615. Measles, 616. DiaiThoeal diseases in general, 616. Sunstroke, 616. Venereal diseases, 617.

Chapter X. Naval And Marine Hygiene 618

Naval recruits, 618. The naval ration, 619. Water supply, 620. The sailor's sleeping quarters, 621. The diseases of the sailor, 622. Ventilation of vessels, 623. Greneral hygiene of ships, 624.

Chapter XI. Tropical Hygiene 627

The soldier and the civilian in the tropics, 627. Habits of life, 629. Diet, 620. The use pf alcohol in the tropics, 631. Clothing, 633. Care of the person, 634. Tropical diseases, 634.

Chapter XII. The Relation Of Insects To Human Diseases 636

Introductory, 636. Flies, 637. Fleas, 640. Bedbugs, 640. Mosquitoes, 641. Mosquitoes and malaria, 642. The malarial parasite, 645. Preventive measures, 651. Mosquitoes and yellow fever, 652. The yellow fever mosquito, 654. Preventive measui-es, 656. Mosquitoes and filarial disease, 657. Mosquitoes and dengue, 659. Mosquitoes and distomiasis, 660.

Chapter XIII. Hygiene Of Occupation 661

Introductory, 661. Classification of occupations, 666. Occupations involving exposure to air vitiated by respiration, 668. Occupations involving exposure to irritating and poisonous gases and fumes, 668. Occupations involving exposure to irritating and poisonous dusts, 674. Occupations involving exposure to infective matter in dust, 680. Occupations mvolving the inhalation of offensive gases and vapors, 681. Occupations involving exposure to extremes of heat, 682. Occupations involving exposure to dampness, 682. Occupations involving exposure to abnormal atmospheric pressure, 682. Occupations involving constrained attitude, 683. Occupar tions involving overexercise of parts of the body, 684. Occupations involving sedentary life, 684. Prophylaxis in general, 684. Employment of women and children, 685.

Chapter XIV

Intitoductory, 686. The census, 687. Estimated population, 689. Increase of population, 690. Population constitution, 690. Registrars* returns, 691.

PAGE

Marriage-rates, 692. Birth-rates, 693. Death-rates, 695. Influence of sex, 695. Influence of age, 695. Influence of race, 696. Influence of density, 697. Weekly death-rates, etc., 698. Zymotic death-rate, 698. Infantile death-rate, 698. High and low death-rates, 700. Correction of death-rates, 701. Classification of causes of death, 702. Registration of sickness, 702. Duration of life, 703. Probable duration of life, 703. Mean duration of life, 703. Expectation of life, 703. Life tables, 704.

Chapter XV. Personal Hygiene 706

§ 1. Cabe of the Person. Baths 706

§ 2. Rbgitlation of the Diet 708

§ 3. Rest and Recreation 708

§ 4. Physical Exercise 709

Effects of active exercise, 709. Circulation and respiration, 709. Skin, 710. Nervous system, 710. Digestive apparatus, 711. Kidneys, 711. Effect of exercise on weight, 711. Amount of exercise required, 712. Kinds of exercise, 713. Golf, 713. Wheeling, 714. Tennis, etc., 714. Rowing, 714.

§ 6. Clothino 714

Color, 714. Texture, 714. Heat conductivity, 715. Hygroscopicity, 715. Materials, 715. Wool, 716. Silk, 717. Cotton, 718. Linen, 719. Rubber, 719. Leather, 720. Fur, 720. Felt, 720. Adulteration of clothing, 720. Chemical analysis, 721. Microscopical examination, 721. Poisonous dyes, 721. Selection of clothing, 722.

Chapter XVI. Vaccination And Other Preventive Inoculations 724

Vaccination, 724. Other preventive inoculations, 729. Asiatic cholera, 729. Bubonic plague, 729. Diphtheria, 731. Typhoid fever, 731.

CHAPTER XVn.

Quarantine, 732. Law of 1893, 734. Interstate quarantine, 738. State quarantine, 738. Sanitary cordon, 740. Municipal quarantine, 740. Camps of detention, 741.

CHAPTER XVin.

DISPOSAL OF THE DEAD 742

Earth burial, 742. Sites for cemeteries, 744. Cremation, 744. History of modem cremation, 746.

PKACTICAL HYGIENE.

Section 1. GENERAL CONSIDERATIONS

Foods may be said to include everything taken into the system capable of being utilized directly or indirectly to build up normal structure, repair waste, or produce energy in any form, but in the common acceptation of the term they include only those substances which can be oxidized in the system, thus excluding water and air, without which the functions of the body can not be performed. Diet is a mixture of food materials of various kinds habitually taken in such quantity as is needed to maintain or improve the condition of the system.

The Nutritiye Value of Foods.

The potential energy of food is measured by the amount of heat which can be obtained by its complete combustion, and is expressed in units of heat or calories. The amount of energy required to raise the temperature of 1 kilogram of water 1° C. is known as a lai^ calorie; that required to raise the temperature of 1 gram to the same extent is known as a small calorie ; thus, 1 large calorie equals 1000 small calories. When the term is used without qualification, large calories are understood. These heat units correspond to 425.5 units of work ; that is to say, the same amount of energy required to raise the temperature of the given weight of water 1° C. is sufficient to raise 425.5 times the weight one meter. The amoimt of work done is expressed in kilogram-meters.

The heat unit of the English system is the amount of energy required to raise the temperature of a pound of water 1° F., and its mechanical equivalent is 772 units of work ; that is to say, the same amount of energy will raise 772 pounds one foot. According to the English method, work done is expressed in foot tons rather than in foot pounds.

The calorimetric values of different food materials express also their

2 ' 17 physiological values as nutriment. Eubner* determined the calorimetric value of the proximate principles as follows :

One gram of proteids =4.1 calories.

One gram of carbohydrates = 4.1 "

One gram of fat = 9.3 "

In the system, the carbohydrates and fets are burned completely to carbonic acid and water, but the proteids leave a residue of urea incapable of still further oxidation. It is estimated that the physiological value of the proteids averages only about 75 per cent, of their calorimetric value.

The calorimetric value of different foods of the several classes is not to be understood as being exactly the same. Thus, two kinds of sugar or two kinds of fat, or two kinds of proteid have not exactly the same calorimetric values, and the figures above given are to be understood only as £iir averages. Rubner ^ has determined by actual experimentation the relative calorimetric values of certain food materials, and has shown that 100 grams of fat are equivalent to 225 of syntonin, or 232 of starch, or 234 of cane sugar, or 243 of muscle fiber, or 256 of grape sugar. In other words, these several amounts of food material are isodynamic.

Amount of Food Necessary.

For the maintenance of a proper degree of health and strength, the individual must ingest an amount of food sufficient to meet the daily loss of nitrogen and carbon. This must necessarily vary according to circumstances, and hence no rule can be laid down to fit all cases. The best that can be done is to make certain general rules based on the amount of work performed, for the greater the amount of work done, the greater the amount of food required to meet the necessary consumption of fuel and to repair the tissues. When performing heavy labor, the naturally increased desire for food is shown particularly in the direction of fats, and secondarily of proteids.

It has been estimated by Voit, after much experimentation and from voluminous data, that a man weighing 70 to 75 kilos (154 to 165 pounds) and working at moderately hard labor 9 to 10 hours a day requires 118 grams of proteids, 56 of fat, and 500 of carbohydrates. This is equivalent to 3054.6 calories, and is regarded generally as the most accurate estimate obtainable. From Voit's and other figures, a number of writers have endeavored to construct standard dietaries for the various conditions of bare subsistence, rest, and the performance of different amounts of daily labor, the subsistence diet being reckoned as sufficient only for the internal work of the body in the absolutely passive condition, and that for rest as meeting the requirements of very gentle exercise.

The constituents of the standard diets are prescribed in the following proportions : For each part of proteids, two-thirds of a part of fiit,

* Lehrbuch der Ilygiene, Leipsic, 1900, p. 438. "Ibidem, p. 430.

COMPOSITION OF FOODS. 19

three and one-sixth parts of carbohydrates, and one-fourth of a part of mineral matter. The proportion of 1 part of nitrogen to 15 of carbon should be maintained as nearly as possible. In all dietaries it is necessary to have the diiferent constituents properly proportioned, and in addition to vary from day to day the articles belonging to the same classes, since otherwise they will become distasteful. The question of nutritive value, while paramount, is not all, for taste and variety of flavor are important in a high d^ree, and the palate must be flattered.

Knowing the composition of various food materials, the nutritive value of a given weight, and problems of supplying given amounts of proteids, fiits, and carbohydrates from means at hand can be worked out mathematically.

Composition of Foods.

The constituents of food materials are partly organic and partly inorganic. The organic constituents include proteids, fat«, carbohydrates, and organic acids ; the inorganic include water and mineral salts.

Proteids. — ^The proteids are the most important constituents of both animal and v^table foods, and their presence is necessary for the carrying on of all the phenomena of life. They are very complex colloid substances composed of carbon, oxygen, hydrogen, nitrogen, and sulphur, possessing common properties and connected in very close genetic relationship. They are divided into animal proteids and vegetable proteids, but between the members of the one class and those of the other there are no important chemical differences, and they are about equal in nutritive value. Some of the vegetable proteids are not colloids, for according to Schmiedeberg, Weyl, Maschka, and others, they are found in crystalline form in the tissues of certain plants, and notably in the bean, pea, lentil, and various nuts.

Proteids when completely split up by acids yield as end products ammonia, nitrogen, organic bases, and amido acids. They are never completely absent from animal and vegetable tissues, but their amount in different substances is very widely variable, some foods being very rich in them, while in others they exist only in traces.

Ingested in great excess of the needs of the system, they are likely to cause general disturbance, diarrhoea and albuminuria, while a diet from which they are practically excluded will cause rapid loss of strength, ansemia, great prostration, and greatly diminished resistance to invasion by specific diseases, especially tuberculosis and pneumonia.

The animal proteids are more rapidly digested than the vegetable proteids, some of which are largely wasted through imperfect digestion. The proteids, whatever their source, yield in the main the same products of digestion, and consequently^ may replace each other in the diet.

The most complete classification of proteids is that of Wroblewski,* by whom they are divided into three groups as follows :

* Berichte der deutschen chemischen Gesellschaft, 1897, 30, pp. 3045, 3052.

Group I. Albuminous bodies closely related to ^g albumin.

1. Albumins. Soluble in water. Egg albumin, serum albumin, laetalbumin, muscle albumin, vegetable albumin.

2. Globulins. Insoluble in water, soluble in dilute salt solution. Egg globulin (vitellin), serum globulin, lactoglobulin, fibrinogen, myosin, v^etable globulin.

3. Proteids soluble in alcohol. Substances very slightly soluble in water and salt solutions, soluble in dilute alcohol, some in strong alcohol. Chiefly of vegetable origin. Very rich in carbon.

4. Albuminates. Products of the action of alkalies on albumins. Slightly soluble in water, easily soluble in alkalies.

5. Acid albumins. Products of the action of acids on albumins. Soluble in very dilute acids and alkalies. Syntonin, etc.

6. Coagulated albumins. Proteid substances coagulated by the .action of heat or enzymes. Fibrin, para-casein, etc.

Group II. Compound proteids composed of molecules which consist of an albumin group (aj) plus another group, usually of a nonproteid nature.

1. Glyco-proteids. Oj plus a carbohydrate group. Mucin, etc.

2. Hsemoglobins. a^ plus a coloring-matter group.

3. Nucleo-albumins. a, plus a nuclein group.

4. Caseins. They contain no true nuclein group. With rennet they give a characteristic coagulation reaction. They are not coagulated by heat like albumin nor by enzyme action like fibrin. Milk casein, legumin, etc.

5. Nucleins. a^ plus a nuclein acid group.

6. Amyloids.

Group III. Albuminoids, a. Frame-work substances.

1. Keratins. Constituents of horn. Attacked with difficulty by pepsin and trypsin. They contain much sulphur and yield much tyrosin.

2. Elastins. Constituents of elastic tissue. They contain less sulphur and yield less tyrosin.

3. CoUagens. Constituents of connective tissue, bone, and cartilage. They contain very little sulphur, and yield no aromatic amido-acids. Gelatin, isinglass, chondrin, collagen, etc.

6. Albumoses and Peptones. Products of hydrolytic splitting of various proteid substances. Their molecules are much smaller than those of the albumins.

c. Enzymes. Bodies which when present in verj' small amounts have the property of breaking up very large amounts of certain other substances, including proteids, fats, starches, etc.

The albumins are not precipitated by alkaline carbonates, common salt, or dilute acids, but they are coagulated by being heated to 65°— 73° C. Casein, legumin, conglntin, syntonin, and albuminates, on the contrary, are not coagulable by heat, but are precipitated by common salt, sodium acetate, and trisodium phosphate. The albumoses are

COMPOSITION OF FOODS, 21

wddely distributed throughout the vegetable kingdom, and are found largely in the cereals. In the animal kmgdom, they are intermediate products of the action of pepsin on ordinary proteids, becoming eventually converted to peptones. The collagens are very rich in nitrogen, but have an inferior nutritive value. Grelatin, for instance, contains 17-18 per cent., while the albumins contain but 16,

Pats. — The fats are compounds of the triatomic alcohol, glycerin, with fatty acids, mainly stearic, palmitic, and oleic. These several compounds are known as stearin, palmitin, and oleiu. The two first mentioned are solids at usual temperatures, while olein is a liquid. Most fats are combinations of two or all of these substances, and some, as, for example, butter, contain additional glycerides in small amount. Stearin and palmitiu being solids, and olein liquid, the consistency of a fat is dependent upon the proportions in which these substances are present. Stearin is a component of most animal fiits, but never is found in vegetable fats. The chief constituent of animal fats is palmitin, and this occurs also in nearly all vegetable fats. Olein exists in both. Butyrin, caprin, caproin, and caprylin are glycerides of volatile fatty acids present in the fat of milk.