The chief index or measure of the health of any locality is what is called “the death-rate” of that locality. Although there are several other important evidences as to the healthiness or unhealthiness of any given area, the “death-rate” is the chief and most obvious indication of the advantageous or disadvantageous action of the conditions of any given city or other chosen area upon human life. Its records are more easily kept with an approach to accuracy than are records of cases of sickness not terminating in death. The cause of death has to be certified in civilised communities by a medical man; the total number of deaths in a year is given by the number of burial certificates. The death-rate is stated at so many per thousand of the population per annum. Thus, in a city of 5 million inhabitants,—that is to say, 5 thousand thousands—a record of eighty thousand deaths in the year gives 16 deaths for every thousand persons living. That is called “an annual death-rate of 16.” The record for any single month may be stated (as it is stated at intervals in the newspapers) “as at the rate of so many in the thousand per annum,” by multiplying the actual monthly number per thousand by 12. Thus, in the case of the city just cited, if the death-rate were the same in every month of the year—namely, 16—it would mean that 6500 persons died regularly every month. But we should probably find that in some month or other as few as 5417 persons died. That would be reported “as at the rate of” 13 per thousand per annum; since, if every month gave only 5417 deaths, we should get 65,000 deaths a year, which works out at 13 in the thousand in a population of 5 millions. In other months it might run as high as 19 or 20 (representing over 8000 deaths a month), although, taking all the months together, the deaths are at the rate of 16 in the thousand for the year.