THE

PRINCIPLES OF HYGIENE.

INTRODUCTION.

THE Comprehensive nature of the subject precludes the possibility of giving a short and precise definition. A late writer on hygiene has given the following definition: "Hygiene aims to make growth more perfect, life more vigorous, decay less rapid, death more remote." Hence hygiene treats of the laws of health; of all those means which tend to preserve the body in a healthy condition, as well as those which tend to improve the general health. It embraces a knowledge of the factors and conditions which bring about ill health and disease, as well as a knowledge of the best means of preventing disease, and of the measures which tend to fortify and improve the organism.

Health is that condition of the body in which all the various functions are performed normally, and without the manifestation of discomfort in any of its operations. Disease, on the other hand, implies the imperfect performance of one or more of the bodily functions because of the impaired structure of the corresponding organ or organs, and the consequent manifestation of discomfort, either in the part directly affected or in the body generally. There are many factors which may operate in such a manner as to bring about disease. These factors are usually divided into the immediate and remote causes of disease.

The immediate causes of disease may be again divided into three classes, physical, chemical, and vital. The

physical causes of disease are such as are brought about by physical agencies. The diseases which are due to physical agencies are burns, cuts, bruises, fractures, and the like, and those diseases of the respiratory organs due to the inhalation of various forms of dust. The chemical causes of disease are corrosive and irritating drugs and chemicals which act directly through their corrosive action upon the part with which they are brought in contact, or indirectly through action upon the system after having been absorbed into the circulation. The vital causes of disease are the most important, because they are the most numerous and are frequently communicated from the sick to the well. They are also of great hygienic importance, because most of them are preventable. The vital causes of disease which are known to-day are the animal and vegetable parasites that are capable of lodging upon the surface of the body or penetrating into the blood and tissues, and thus give rise to disordered function either by producing obstruction, local irritation, absorbing large quantities of nourishment from the body, or by generating highly poisonous secretion and excretion products which produce disease through their local or general action. The principal animal parasites which produce disease are the various forms of intestinal worms, the trichina spiralis, the filariæ, the itch mite, and the malarial organisms. The principal vegetable parasites which produce disease are the different forms of pathogenic bacteria and the plants of somewhat higher order which produce tinea favosa and other skin diseases.

The remote causes of disease operate in such a manner as gradually to reduce the physical powers of the body, so as to make it possible for the vital causes to operate. The remote causes of disease may be such factors as undue exposure to extremes of heat and cold, dampness or undue dryness of the atmosphere, undue exposure to bright lights or strong currents of air may operate in this manner, prolonged absence of sunlight, deficient ventilation, the use of excessive amounts of

certain kinds of food and drink, the continued use of a diet which is deficient in one or more of the elements which enter into the composition of the body, maintaining the body in abnormal positions for a long time, undue physical or mental exertion, deprivation of food and sleep, and wearing of apparel which constricts certain portions of the body.

The causes of disease may also be divided into the predisposing and the exciting causes. The predisposing causes of disease are the various conditions which, by their influence upon the body, render it less resistant to the invasion of pathogenic bacteria, or otherwise predispose to disordered health. The conditions which have been classed as remote causes of disease also belong in this class; but besides these there are other important conditions which predispose to disease, such as the age and sex of a person, hereditary influences, race, conjugal condition, the hygienic condition of the environment, the density of the population, the nature of the occupation, and the climate of the locality. Dr. Farr found that the mortality increases with the density of the population, but not in direct proportion to the density, but as its sixth root.

The exciting causes of disease are the specific elements which are the etiologic factors in the production of disease. These are synonymous with the immediate causes of disease in the first classification, the physical, chemical, and vital causes of disease.

Predisposing Causes of Disease.-1. Age.-The influence of age is a most important factor in the production of disease. The age groups at which the mortality is greatest are to be found in the periods of growth and decline, while the mortality is lowest during youth and the earlier periods of adult maturity. The highest mortality occurs among children under one year of age, and then decreases rapidly until we reach the fifteenth year, after which it again gradually increases until we reach the period between sixty and seventy years, when

it again decreases. The following table, taken from the annual reports of the Bureau of Health of the city of Philadelphia, shows "the percentage of deaths to total mortality during specified periods of life," for the years 1889 to 1894, inclusive:

The high infantile mortality is due, primarily, to the effects of faulty nutrition, owing to the fact that so many infants must be nourished by means of artificial foods. The secondary causes of the high infantile mortality are the acute catarrhal inflammations of the gastro-intestinal and respiratory tracts. The following table shows the relative frequency of the diseases of the type of acute catarrhal inflammations of the gastro-intestinal and respiratory tracts as compared with the death-rate from the acute infectious diseases, of diseases of the nervous system, and the deaths from all causes in children under one year of age, in Philadelphia during the years 1890 to 1894, inclusive: