In regard to poisons, there are wide differences between the sexes, probably owing to the fact that males have freer access to and therefore a wider choice of poisons, and are also better informed on the subject. Out of every 1,000 males who poisoned themselves during 1871-80, 567 used narcotic poisons; while of 1,000 women who poisoned themselves, only 246 had recourse to these. On the other hand, strychnine, or vermin killer, arsenic and phosphorus, carbolic acid and vitriol, spite of the acute sufferings they produce, were used by women in 544 cases out of 1,000, against 246 cases out of 1,000 in which they were used by male suicides.

As regards the local distribution of suicide, the total deaths from this cause in each county are too small to form a trustworthy basis for calculation. It would appear, however, that suicide is much more common in the educated than in the uneducated classes (Registrar-General's 45th Report), as shown in the following table :

N.B. The proportions of persons unable to write are the averages of the 10 years 1869-78.

Homicide (including manslaughter and murder) was the registered cause of 352 deaths in 1887, or 12 per million persons, 199 being returned as murder and 153 as manslaughter.

Bv execution 21 deaths occurred during 1887, a larger number million liv ny year since 1877. In the 24 years, 1863-86, only one criminal was hanged to 15.5 recognised murders, while the proportion was 1 to 9.5 murders in 1887.

CHAPTER XIV.

LIFE TABLES.

Dr. Farr's Biometer.-Data for Life Table.-Method of Construction of Life Table.-Shorter Method of Dr. Farr.-Mr. Noel Humphrey's Method.History of Life Tables.-Halley.-De Moivre's Hypothesis.-Dr. Price's Northampton Table.-Mr. Milne's Carlisle Table.-Dr. Farr's English Life Tables No. 1 and No. 2.-English Life Table No. 3.-Normal or Life-Table Population.-Healthy Districts Life Table.-Upper-Class Experience Table.-Healthy Males Table.-Clerical Experience Table.— Dr. Ogle's New English Life Table.

L'

IFE Tables afford an accurate means of measuring the probabilities of life and death. They represent "a generation of individuals passing through time," the data on which they are founded being the number and ages of the living, and the number and ages of the dying. Dr. Farr calls the Life Table a biometer, and speaks of it as of equal importance, in all inquiries connected with human life or sanitary improvements, with the barometer or thermometer and similar instruments employed in physical research; and as being also the keystone or pivot on which the whole science of life assurance hinges. Even supposing that an insurance society had empirically arrived at an equitable rate of premium for assuring lives, the Mortality or Life Table is still required in order to ascertain the value of such premiums for a prospective term of years, as against the value of the sums assured thereby, so that a statement of assets and liabilities may be periodically prepared. Without such knowledge a division of " profits" would be impossible. In fact the Life Table is absolutely essential for "the solution of all questions depending on the duration of human life."

Addison in his "Vision of Mirza," possibly writing with Halley's graduated Life Table before him, gives the following allegory :

"The bridge thou seest, said he, is Human Life; consider it attentively. Upon a more leisurely survey of it, I found that it consisted of threescore and ten entire arches, with several broken arches, which, added to those that were entire, made up the number about an hundred. As I was counting the arches, the Genius told me that this bridge consisted at first of a thousand arches; but that a great flood swept away the rest, and left the bridge in the ruinous condition I now beheld it. But tell me further, said he, what thou discoverest on it. I see multitudes of people passing over it, said I, and a black cloud hanging on each end of it. As I looked more attentively, I saw several of the passengers dropping through the bridge into the great tide that flowed underneath it: and upon further examination perceived that there were innumerable trap-doors that lay concealed in the bridge which the passengers no sooner trod upon, but they fell through them into the tide, and immediately disappeared. These hidden pit-falls were set very thick at the entrance of the bridge, so that throngs of people no sooner break through the cloud, but many of them fell into them. They grew thinner towards the middle, but multiplied and laid closer together towards the end of the arches that were entire. There were, indeed, some persons, but their number was very small, that continued a kind of hobbling march of the broken arches, but fell through one after another, being quite tired and spent with so long a walk."

Without discussing the duration of life in the antediluvian age, we have here a graphic narration of the "hidden pitfalls and trap-doors," and the "broken arches," which beset the course of human life, and the beautiful simplicity of the description forms a useful comment on the diagram at page 236-7.

Description of Life Table.—The essential portions of a Life or Mortality Table are the number and ages of the living and the number and ages of the dying.

1. Suppose that we could observe a million children, all born

at the same moment, and follow them throughout life, entering in a column the number who remain alive at the end of each successive year until all have died. This column is headed by the symbol ; where 7 represents the number who reach the precise age x.

In a second column we record the number dying before the completion of each year of life. Thus the number who die before reaching the first anniversary are placed opposite the age O in the table, and so on. In this way we obtain the column headed d; where d, represents the number out of 7, persons attaining the precise age x, who die before reaching the age x+1. It is evident, therefore, that

d=l,-l,+1

i.e., the number dying between the ages x and x+1 is equal to the difference between the numbers living at the ages x and x+1.

In practice it is not possible to observe a body of children throughout life in the precise manner indicated, so that other methods must be resorted to.

2. It is not necessary to assume, as in the preceding case, that all the persons observed have been born at the same time. If we could trace any 1,000,000 children throughout life, however various might be the dates of their births, a Life Table might be similarly constructed, if the numbers living and dying during each year of life were known.

Our national records do not lend themselves to this method, but Friendly Societies and Life Assurance Offices, as well as Annuity and Pension Institutions, afford the requisite data for observing individual lives and thus constructing a trustworthy Life Table, though seldom in so complete a form as to cover the whole period of life from birth to death.

3. Without tracing the history of individual children through life, we may, by taking a complete census of the population, distributed according to age and sex, obtain data for forming the column . Similarly, from the annual death-returns, we obtain the number dying during each year of life, and thus form

the column d; and from these data can estimate the number of deaths per unit of population which forms the column headed m

The method usually adopted in constructing a Life Table is a modification of this. The number of persons dying within a given period and their ages at death are observed, and it is assumed that the mortality for any year of age thus obtained will be applicable to other lives in the Table, as they successively attain the age in question. In the same way the number out of a million persons, living at each age or group of ages is ascertained from a single census or by combining the results of two or more census enumerations. By these means results are obtained which, being wholly based on recent observations, will probably be more correct, as indicating the present conditions affecting the duration of life, than if a million persons were watched from birth to death; for, in the latter case, the conditions which determined the rate of mortality might, before the series was available, have undergone great changes, and for practical purposes the table be almost valueless.

Dr. Farr's English Life Table, No. 3, was based on the registered deaths in England and Wales during the seventeen years 1838-54, and on the two census enumerations of population in 1841 and 1851. Dr. Ogle's Life Table is based on the mean population of the decennium 1871-80, and on the total deaths during the same decennium. A comparative view of these two tables is given on page 238.

Method of Construction of Life Table.-It is evident that the deaths in a population, during any stated year, do not occur simultaneously either at the beginning or the end of the year, but are distributed throughout its course. It is also evident

* The ratio of deaths to mean population, or my, has been called by Farr the rate of mortality, and we follow his notation and system; but actuarial writers reserve the name rate of mortality for the probability of dying within a year (q). The name central death-rate has been given by these writers mx, because it represents the rate at which people are dying in the centre of the year x to x+1.

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