not only causes an excess of the infantile population, among whom the mortality is great, but also an excess of persons between 10 and 40 years of age, among whom the mortality is low.

Birth-Rates and Death-Rates in 1887.

That a high birth-rate and a high death-rate commonly co

1

exist is certain, though the concurrence is by no means constant nor do the variations in the two follow on equal lines, as shown in the preceding table, in which the towns are arranged in order of their death-rates (page 85).

If a high birth-rate is necessarily followed by a high deathrate, the former must be regarded as an indication of a low sanitary condition. It is difficult to believe, however, that an increase of reproductive power argues a depression of vitality. The greater fertility in crowded districts is explained by the much higher proportion of people at child-bearing ages, owing to the inrush of young workers in search of the higher town wages. That there should be a high death-rate in such populations is in spite and not in consequence of the high birthrate; and the high death-rate is due in reality to density of population and its concomitant social and sanitary evils. When a high death-rate follows a high birth-rate, it is due largely to excessive infantile mortality. Infants form a delicate index. to the sanitary status of a population.

Low birth-rates and low death-rates also usually coexist. But the conclusion that one causes the other is altogether untenable. In France there is a low birth-rate and a high death-rate, owing largely to the fact that the continuous low birth-rate has caused the average age of the population to be considerably higher than in this country. On the other hand, in Staffordshire and Durham, in which the excess of births over deaths is very great, the death-rate is by no means the highest (see table, page 58).

To sum up: Dr. Farr has clearly shown that populations having a continuously high birth-rate, should (sanitary conditions being equal) have lower death-rates than populations having low birth-rates, because a continuously high birth-rate means an exceptionally large proportion of young adults in a population, and consequently an unduly small proportion of old people. Conversely, a low birth-rate means a small proportion of young adults and a large proportion of adults and old people, and is therefore unfavourable to a low death-rate.

The same conclusions are clearly demonstrated by Mr. N. A.

Humphreys, in his paper on "The Value of Death-Rates as a Test of Sanitary Condition." He takes as examples the birth and death-rates of three agricultural and three urban counties in 1871, and finds the normal death-rate in the two groups by allowing for varying age-distribution. The result is shown in the following table :

It might be assumed that the higher death-rate of the urban counties is explained by their higher birth-rate; but when correction is made for different age-constitution of the two populations, it is seen that, all sanitary conditions being equal, the age-constitution of the urban populations favours their death-rate to the extent of 1.8 per 1,000, instead of in any way explaining the high death-rate, as maintained by Dr. Letheby and others.

Influence of Age and Sex-Distribution on Death-Rate.-We shall consider at this point the modifications in the general death-rate which may result from varying age and sex-constitution of a population, reserving to the next chapter the consideration of death-rates at different ages.

Dr. Ogle has summed up the matter in the following words: "It is necessary to point out that two places might be on a perfect equality with each other as regards their climate, their sanitary arrangements, their closeness of aggregation, as also the habits and occupations of their inhabitants, and yet might have very different general death-rates, owing to differences in the age and sex-distribution of their respective populations. Such a supposed case is, of course, scarcely likely to present itself; for when the prevalent occupations are the same in two places, the age and sex-distribution is almost certain to be the

same also. But in places where the prevalent occupations are not the same, there are often very great differences in the age and sex-distribution of the populations, and such as seriously affect the general death-rates."

The age and sex-distribution in any district determine mainly the prevalent occupations; and as the occupations remain fairly constant, the age and sex-distribution likewise vary but little. Thus no difficulty arises in comparing the death-rate of the same district or town at different periods. It is only when different districts or towns are compared that the necessity for correction (and ofttimes considerable correction) arises. The differences due to varying sex-distribution are usually very small, and it therefore generally suffices to correct for age-distribution.

In order to appreciate the influence on the death-rate of varying age and sex-distribution, we must examine the deathrates at different age-groups and in the two sexes. These are shown for four decennia in the following table from Dr. Ogle's Supplement to the 45th Annual Report of the RegistrarGeneral:

Annual Mortality per 1,000 of Males and Females in
successive Decennia.

1841-50. 1851-60. 1861-70. 1871-80. 1841-50. 1851-60 1861-70. 1871-80.

25

35

45

55

65

23.11 23.05 23.61 22.61 21.58 21.32 21.28 20:00

71-20 72.43 73.16 68.14

9.16 8.51 8.15

6.67

5.12 4.88 4.46

3.69

61.09 62-74 63.43 58.10 8.89 8.42 7.76 6.20 5.42 5.06 4.48 3.70 7.05 6.69 6.16 5.23 7.88 7.38 6.62 9.50 8.83 8.45 7.32 9.08 8.53 7.96

5.43

6.78

10.55 9.92 9.68 8.58 12.91 12-15 12.03 11.58 16.04 15-20 15:55 15:59 28.44 27.01 27-77 28.54

9.94 9.57 9.90 9.30 12.85 12:48 13:46 13.74 18.22 17.96 19-16 20:05 31.81 30.85 33.00 34.76 67.51 65.33 66.69 69-57 60.97 58-66 58.80 60.82 75 & upwards 168-56 165 40 164.64 169 08 157.89 155-45 154-28 155.83

The table shows that between the ages of five and fifty-five the death-rate per 1,000 living at each group of ages is lower than the death-rate for all ages. It is evident, therefore, that an unusually large proportion of persons living at these ages would be a cause of low mortality. Under five and over fiftyfive the death-rate is higher than the death-rate for all ages; and an excess of population at these ages would consequently raise the general death-rate.

The age-distribution of populations is therefore of great importance in determining the relative value of their deathrates. If they are identical in two localities, then any differences in their death-rates may be referred to influences peculiar to each place. As Farr puts it, "Independently of other causes of variation, the mortality of different populations will differ according as they consist of numbers in various proportions at the ages at which the mortality is high or low." The same reasoning applies for sex-distribution. At nearly all ages the death-rate of females is lower than that of males. Consequently an excess of females (as in residential neighbourhoods with a large number of domestic servants) must tend to lower the death-rate of a district, without implying a necessarily better sanitary condition.

Number of Males living to every 100 Females living (exclusive of the portion of the Army, Navy, and Merchant Seamen abroad).

The preceding table shows that, spite of the excess of male