owner. No charge is made for these services, and disinfection is compulsory in every case. The practice in Philadelphia and other large cities is quite similar to that in New York.

The infectious diseases in which notification is compulsory in Philadelphia are: Cholera, small-pox, diphtheria, diphtheritic croup, membranous croup, scarlet fever, measles, typhoid fever, typhus fever, epidemic cerebrospinal fever, relapsing fever, and leprosy. Knowledge of cases of diphtheria reaches the department of health through the forwarding of a culture to the bacteriologic laboratory for examination, as well as by notification by the physician. If, on examination, the culture is found to contain diphtheria bacilli, the case is at once reported to the medical inspector, at the same time that a report is forwarded to the attending physician. In this manner doubtful cases are diagnosed early, and no hardships are entailed upon the suspect or the family, while the community is protected by prompt isolation of all such cases. The contagious character of tuberculosis in all its forms is becoming more and more generally recognized. Nevertheless there is strenuous opposition from many sources to the notification of cases of tuberculosis. In New York and Philadelphia such notification is now required, not with the idea of quarantining the cases, but in order to keep informed as to their location, and to make it possible to direct approved prophylactic measures against the spread of the disease from the sick to the well. general disinfection of the premises occupied by cases of tuberculosis in the tenement district is attempted. On the other hand, all such premises are thoroughly renovated after the removal or death of the tubercular patient. In this manner the danger from infection through infective dust is greatly lessened. The work of the department is hampered, however, because of the absence of sufficient hospital accommodations for consumptive poor. Most beneficial effects have, however, already resulted from the various measures instituted for

No

the prevention of tuberculosis, as shown in the very material decline in the number of deaths occurring from it.

The investigations of Anders and of Flick, of Philadelphia, and those of Biggs, of New York, show that tuberculosis is not uniformly diffused through a community, not even in those localities where it occurs most frequently, but is confined largely within narrow boundaries, as in certain streets and within the walls of certain houses. These investigations have shown that when a house is once infected, repeated cases are developed in it from the new tenants occupying such a house. These infected houses are most frequently found in the narrower streets, in courts, and in alleys. Though there is some danger of infection from the inhalation of dust in the open air in crowded parts of the city, it seems probable that a more prolonged exposure to a concentrated atmosphere of infection, as found in these infected houses, is the most frequent mode of contracting the disease. The dust in street-cars and various public places is often infected, and may lead to contraction of the disease. The prohibition of spitting on the floor of cars, ferryboats, and other public conveyances should, therefore, be strictly enforced as a wise sanitary measure.

CHAPTER XX.

VITAL STATISTICS.

VITAL statistics includes the records of all circumstances affecting the production and duration of human life, and corresponds to the term "démographie" employed by French writers. The registration of vital statistics includes the obtaining of records of births, deaths, marriages, and disease. The comparison of these records with each other, and with the statistics of the living population, comprises vital statistics proper.

The systems of registration employed by different. States and cities differ as to details. They include a periodical report of the births, with date and place of birth, sex, color, and nationality of the child, and the names, residence, birthplace, age, and occupation of the parents. These reports are usually made monthly by the physician to the health bureau of the city. Deaths are reported through the physician and undertaker to the health authorities, who issue a burial permit. The information furnished on the death certificate includes the age, sex, color, nationality, and conjugal condition of the deceased, as well as the immediate and remote causes of death. In the United States the physician acts in a judicial capacity in reporting a death. Upon this fact is based the right of legislation regulating the education and qualification of medical men and the laws regulating the practice of medicine. He is a State officer in relation to his knowledge of the cause of death.

The cases of infectious diseases are reported at once by the physician when the diagnosis has established the nature of the disease. Up to the present time only a few States have had an accurate system of registration. With the beginning of the twentieth century a number

of States and cities, as well as a large number of other countries, will adopt a uniform system of classification of the causes of death, known as the Bertillon system. This system has been adopted generally after repeated conferences extending over a number of years. Dr. Bertillon presented his system of classification to the International Statistical Institute at Chicago in 1893. It has since received the endorsement of the American Public Health Association, the International Conference of State and Provincial Boards of Health of North America, and received its first International Decennial Revision at Paris in 1900. By the use of this uniform system of classification the vital statistics of different countries will be readily comparable. It is safe to presume that the general adoption of such a uniform system of classification, with decennial revisions of the same by those using it, will lead to more efficient registration methods wherever the system is employed. Full information as to the details of the Bertillon system of classification may be found in the publications of the American Public Health Association, of the Michigan Division of Vital Statistics, and the United States Marine-Hospital Service. Requiring a permit for burial is the only reliable means of obtaining the desired information. This is necessary to secure a proper inheritance of property. It also aids in detecting crime.

By means of an accurate system of registration a community is able to keep informed as to the condition of the public health, the efficiency of quarantine measures, the purity of the water-supply, and the death-rate from all diseases. The value of estimates made from vital statistics as reported to the health authorities is dependent upon a knowledge of the living population. In most countries this is determined decennially by means of a national census. Some cities have an additional census taken midway between the decennial censuses. In the absence of such special censuses the calculations are based on the results of the decennial censuses. The

Registrar-General of Scotland employs the following method for calculating the population for the inter-census years: He assumes that the rate of increase as ascertained from the two enumerations immediately preceding continues the same during the course of the next ten years. The sanitary department of Glasgow ascertains the number of houses inhabited by the census population, the average population per house, and then in each succeeding inter-census year applies this average as a multiplier to the inhabited houses for the year, as entered upon the rolls of the assessor. Neither of these methods gives accurate results. Since population increases in geometric proportion, the arithmetical mean may be taken between two censuses. The result will generally be less than normal, but will not vary more than 1 per 1000 in the death-rate as calculated from these data as compared with the results obtained from actual enumerations.

The Census as a Basis for Calculation.-It is essential, therefore, that an accurate census of the population be taken at stated intervals to form the basis of calculation of the results obtained from registrations of births, deaths, marriages, and disease. The density of population, or the number of persons occupying a definite area, is also of value, and this is obtained by dividing the population by the area in square meters, square miles, or in acres.

Standards of Age-distribution.-In order to make it possible to secure fair comparisons of the death-rates of different places, a uniform standard should be adopted to which all populations may be referred, or with which they may be compared. The committee on nomenclature of the American Public Health Association, in its report for 1895, states that, other things being equal, a city in which the persons living under one year of age, and those who are more than fifty years of age, constitute together more than 15 per cent. of the population, will have a higher death-rate than another city under similar conditions in which the persons of these ages constitute