VITAL STATISTICS.
Vital Statistics is the science of numbers applied to the life-history
of communities. Its significance is similar to that of the more
recently coined word—Demography—though the latter does not necessarily
confine itself strictly to study of life by statistical means. Another
term has been frequently used in recent years—“Vital and Mortal
Statistics.” The continued use of the word “mortal” in this connection
is undesirable and objectionable. The term “Vital Statistics” is
comprehensive and complete, as death is but the last act of life.
Of the problems of life with which the science of Vital Statistics is
concerned, population, births, marriages, sickness, and deaths, possess
the chief importance; and in the following sketch of the subject
I shall concern myself chiefly with these. The subject naturally
divides itself into two sections: the sources of information, and the
information derived from these sources, and both of these will require
consideration.
The importance of numerical standards of comparison in science
increases with every increase of knowledge. The value of _experience_,
founded on an accumulation of individual facts, varies greatly
according to the character of the observer. As Dr. Guy has put it:
“The _sometimes_ of the cautious is the _often_ of the sanguine, the
_always_ of the empiric, and the _never_ of the sceptic; while the
numbers 1, 10, 100, and 100,000 have but one meaning for all mankind.”
Hence the importance of an exact numerical statement of facts. The
sneering statement that statistics cannot be made to prove anything can
only be made by one ignorant of science. In fact, nothing can be proved
without their aid, though they may be so ignorantly or unscrupulously
manipulated as to appear to prove what is untrue. Instances of
fallacious use of figures will be given as we proceed.
An accurate statement of =population= forms the natural basis of all
vital statistics. Thus the comparison of the number of deaths in one
with the number of deaths in a second community has no significance
unless we know also the number living out of which these deaths
occurred. Even then our knowledge would be defective, without further
particulars as to the proportion in each population living at different
ages, and the number dying at the corresponding ages. For other
purposes we should require to know the number married and unmarried,
the number engaged in different industries, and so on; in order that
the influence of marital conditions, of occupation, etc., on the
prospects of life may be calculated. The first desideratum of accurate
vital statistics is a =census enumeration= of the population at such
intervals as will not cause the intervening estimates of population
to be very wide of the mark. In this country a decennial census is
taken, the last occurring in 1901. In the intervals the population of
the entire country, and of each town or district is estimated. Various
methods of =estimating the population= have been adopted. (1) If a
strict record of emigration and immigration is kept, then in a country
in which a complete registration of births and deaths is enforced, the
population can be easily ascertained by balancing the natural increase
by excess of births over deaths, and the increase or decrease due
to migration. This is done in New Zealand, but is impracticable in
England, as no complete account of migration can be kept.
(2) The increase of inhabited houses in a district being known year by
year, the increase of population may be estimated on the assumption
that the number of persons per house is the same as at the last census.
This may not be strictly accurate. In 1901 it was found that in England
and Wales the average number of persons per house was fractionally less
than in 1891.
(3) It may be assumed that the annual increase during the present
decennium will be 1∕10 of the increase during the last decennium
1891-1901. If so, the population, _e.g._ in 1905, is the enumerated
population in 1901 _plus_ 4¼ times the annual increase occurring
during 1881-91. (The _fourth_ is required because the census is taken
early in April, and the population is estimated to the middle of the
year). This method is fallacious, because it makes no allowances for
the steadily increasing numbers who year by year attain marriageable
age and become parents. It assumes, in other words, simple interest,
when compound interest is in operation.
(4) The Registrar-General’s method, the one generally adopted, assumes
that the same _rate of increase_ will hold good as in the preceding
intercensal period, _i.e._ that the population increases in geometrical
progression, and not in arithmetical progression as under (3).
The application of this method will be best understood by an example.
If the census population of a town is 32,000 in 1891, and 36,000 in
1901, what is the mean population in 1905?
(_a_) _Find the rate of increase in 1891-1901._
If P = population at census 1891,
and if P^{1} = „ „ 1901,
and if R = rate of increase of population, then
P^{1} = P - R^{_n_} in the _n_th year.
log P^{1} = log P + 10 log R.
1∕10(log P^{1} - log P) = log R.
(4·556303 - 4·505150)∕10 = ·0051153 = log R.
(_b_) _Apply this to the increase in the next 4¼ years._
Here P_1905 = P_1901 R^(17∕4)
log P_1905 = 4·556303 + (17∕4) (·0051153)
= 4·578043.
By consulting the table of logs, the population corresponding to this
number will be found to be 37,848 = population at the middle of 1905.
Estimates made by the last-named “official” method are liable to error,
even for the entire country, and still more when applied to special
districts. Thus the decennial rate of increase of the population of
England and Wales in the 100 years has varied from 15·8 per cent. in
1821-31 to 11·6 per cent. in 1891-1901. The anomalies are even greater
when the official method is applied to great towns. In one decennium
such a town may, owing to brisk trade, have a rapid increase of working
population with many children, and in the next decennium in consequence
of emigration or transmigration there may be little or no increase.
The declining birth-rate, which is having a greater effect on the
number of population than the declining death-rate, is another cause
of disturbance which increases the difficulty in forming a correct
estimate of the population in intercensal periods. A quinquennial
census is highly desirable, in order to avoid the doubts necessarily
associated with estimates of population in the later years of a
decennium, and with the birth and death-rates which are based on these
estimates.
=The Registration of Births and Deaths.=—Civil registration of births
and deaths began in 1837, but was not compulsory till 1870. It will
be going beyond the scope of this chapter to give details of the
enactments as to registration. It suffices to state that it is the
duty of the practitioner to give a certificate stating the cause of
death of his patient to the best of his knowledge and belief. There
is no registration of still-births in this country. Many deaths are
registered of which the cause of death is not medically certified,
and the value of our national vital statistics is considerably
diminished on this account. Much improvement is desirable in the
medical certification of causes of death. Every medical student ought
to receive instruction on this subject before the completion of
his studies. Names of symptoms as dropsy, hæmorrhage, convulsions;
and obscure names, as abdominal disease, should be avoided. If the
patient has recently suffered from injury, or recently passed through
childbirth, or had a specific febrile disease, this must not be omitted
from the certificate.
=The Registration and Notification of Sickness= forms another valuable
source of information. Various attempts have been made to secure a
general registration of disabling sickness, but with only partial
success. District and workhouse medical officers appointed since
February, 1879, are required to furnish the medical officer of health
with returns of pauper sickness and deaths. This source of information
might with advantage be more fully utilised by medical officers of
health. Sec. 29 of the Factory and Workshops Act, 1895, requires that
every medical practitioner attending on or called in to visit a patient
whom he believes to be suffering from lead, phosphorus, or arsenical
poisoning, or anthrax, contracted in any factory or workshop, shall
send to the Chief Inspector of Factories at the Home Office, London,
a notice stating the name and full postal address of the patient, and
the disease from which he is suffering; a fee of 2s. 6d. being payable
for each notification, and a fine not exceeding 40s. being incurred for
failure to notify.
=The Compulsory Notification of Infectious Diseases= is enforced by
the Act of 1889, which now applies to the whole country. The list of
diseases to be notified is as follows:
“Small-pox, cholera, diphtheria, membranous croup, erysipelas, the
disease known as scarlatina or scarlet fever, and the fevers known
by any of the following names: typhus, typhoid, enteric, relapsing,
continued, or puerperal, and also any infectious disease to which the
Act has been applied by the Local Authority in manner provided by the
Act.”
It is the duty of the medical practitioner to ascertain whether in his
own district, such diseases as whooping cough and measles have been
added to the schedule of notifiable diseases. It is the duty of (_a_)
the head of the family to which the patient belongs; in his default, of
(_b_), the nearest relatives in the house; in their default, of (_c_),
every person in attendance upon the patient; and in default of any such
person, of (_d_) the occupier of the building, as soon as they become
aware that the patient is suffering from an infectious disease to which
this Act applies, to send notice thereof to the Medical Officer of the
District. (_e_) The more formal duty of sending to the Medical Officer
of Health a certificate stating the name of the patient, the situation
of the building, and the infectious disease from which in his opinion
the patient is suffering, is imposed on every medical practitioner
attending on, or called in, to visit the patient, on becoming aware
that the patient is suffering from an infectious disease to which this
Act applies. He is entitled to a fee of 2s. 6d. if the case occurs in
his private practice, and of 1s. if the case occurs in his practice
as medical officer of any public body or institution. He is subject
to a fine not exceeding 40s. if convicted of failure to notify. The
value of returns of infectious diseases as enabling preventive measures
to be taken is increased by interchange of notification returns of
different districts. This is now undertaken weekly for a large number
of districts by the Local Government Board, and the Registrar-General
publishes quarterly summaries of such returns, as well as weekly
returns of infectious diseases for the metropolis.
=Marriages= are usually stated in proportion to the total population,
or the number per thousand of population; but a more accurate method
would be to base the marriage-rate for comparative purposes on the
number of unmarried persons living at marriageable ages. In England the
marriage-rate is always higher in large towns than in rural districts.
Thus in 1900 the marriage-rate in London was 17·6 as compared with an
average marriage-rate in 1891-95 of 15·2 per thousand of the estimated
population in England and Wales. The higher marriage-rate in towns is
chiefly owing to the fact that higher wages and greater scope for
remunerative work attract young country people of marriageable ages to
towns.
=Births= are usually reckoned as a rate per thousand of population.
Clearly, however, if one population had a larger proportion than
another of women of child-bearing years this method of comparison
would not be free from possible error. Even were the proportion of
women of child-bearing ages equal, the comparison might be fallacious
if in one population the proportion of single women was much higher
than in the other. Illegitimate births do not materially vitiate this
conclusion, as such births do not constitute more than 4 per cent. of
the total births, and this number is not excessive in the districts in
which there is the greatest excess of single women, viz. in districts
in which a large number of domestic servants are employed. The only
strictly accurate method is to subdivide the births into legitimate
and illegitimate, stating the former per 1,000 married women of
child-bearing years, and the latter per 1,000 unmarried women of
child-bearing years. I append an example of the relative accuracy of
the three methods above indicated[12]:—
┌─────────────────────┬────────────────────────────────────────┐
│ │ BIRTH-RATE │
│ ├──────────────┬────────────┬────────────┤
│ │ │ │ PER 1,000 │
│ │ PER 1,000 │ PER 1,000 │ MARRIED │
│ │ INHABITANTS. │ WOMEN │ WOMEN AGED │
│ │ │ AGED 15-45.│15-45 YEARS.│
├─────────────────────┼──────────────┼────────────┼────────────┤
│ _Kensington_ │ 21.8 │ 61.6 │ 215.4 │
│ _Whitechapel_ │ 39.9 │ 172.1 │ 328.3 │
├─────────────────────┼──────────────┼────────────┼────────────┤
│_Percentage excess │ 83% │ 179% │ 53% │
│ of birth-rate in │ │ │ │
│ Whitechapel over │ A │ B │ C │
│ that in Kensington_│ │ │ │
└─────────────────────┴──────────────┴────────────┴────────────┘
Thus, according to the ordinary method (A) of stating the legitimate
birth-rate, it is 83% higher in Whitechapel than in Kensington,
whereas it is really only 53% higher. Similarly a statement of the
illegitimate birth-rate in the two districts “per 1,000 inhabitants,”
shows an excess of only 6% in Whitechapel, while a statement “per
1,000 unmarried women aged 15-45 years” shows the real excess of
144%. Both in this and other civilised countries there has been in
the last 25 years a steady decline in the birth-rate. In England the
maximum birth-rate was 36·3 per 1,000 of population in 1876, and the
minimum 29·3 in 1899. This diminution is only caused to a minor degree
by postponement of marriage to more mature years, and by a larger
proportion of celibacy. Nor is there any reasonable ground for the view
that a diminished power of either sex to produce children has been
produced by alcohol, syphilis, tobacco, or other causes. The main cause
of the diminution of the birth-rate is “the deliberate and voluntary
avoidance of child-bearing on, the part of a steadily increasing number
of married persons.”
=Deaths= are calculated in proportion to every 1,000 of the population,
the unit of time being a year. This unit is preserved even when
death-rates for shorter periods, _e.g._ a week, are stated. Thus the
death-rates for the 33 great towns published weekly in the chief
newspapers are _annual death-rates_; they represent the number who
would die per 1,000 of the population, supposing the same proportion
of deaths to population held good throughout the year. The best plan
to obtain the weekly annual death-rate is as follows: the correct
number of weeks in a year being 52·17747, if the population of a town
be 143,956, and the number of deaths in a given week are 35, then the
death-rate is 12·687. Thus:—
143,956∕52·17747 = 2758. 1,000∕2,758 = 0·3625. This is the factor by
which the weekly number of deaths must be multiplied.
35 × 0·3625 = 12·6875 or 12·7.
The above is the _crude death-rate_. Various corrections are required,
which must now be considered. The most important of these are for
public institutions, for visitors, and for age and sex. A public
institution, _e.g._ a workhouse, infirmary, or asylum, in a given
district may consist almost entirely of persons belonging to another
district. The rule is to relegate to the district to which they belong
all deaths of inmates of an institution, _i.e._ subtract all deaths
of outsiders occurring in inside institutions, and add all deaths of
inhabitants occurring in outside institutions. The population as well
as the deaths of these institutions should be excluded, in so far as
they are derived from the outside district, in order to make the net
death-rate approximately correct.
Theoretically the correction ought to be extended so as to apply
to visitors who do not die in public institutions. In practice,
however, this cannot be effected, until a central “clearing house” is
established. The exclusion of deaths of visitors from the district
in which they occur is easy; their inclusion in the returns of the
district from which they come is more difficult to secure. For the
present, they should be included in the death-rate of the district in
which they occur.
=Death-rate according to Age and Sex.=—To obtain a true conception of
the death-rate in a community, it is necessary to state the number of
deaths in each sex in proportion to the number living at different
ages. The importance of this is shown by the following extract from the
Registrar-General’s report for 1899.
England and Wales.—_Deaths to 1,000 living at each of 12 groups of
ages._
┌─────────┬───────┬──────┬─────┬─────┬─────┬─────┬─────┬──────┐
│ │ ALL │ AGED │ │ │ │ │ │ │
│ │ AGES. │ 0─ │ 5─ │ 10─ │ 15─ │ 20─ │ 25─ │ 35─ │
├─────────┼───────┼──────┼─────┼─────┼─────┼─────┼─────┼──────┤
│_Males_ │ 19·5 │ 60·4 │ 3·8 │ 2·2 │ 3·6 │ 5·3 │ 7·1 │ 12·3 │
│ │ │ │ │ │ │ │ │ │
│_Females_│ 17·3 │ 50·7 │ 3·9 │ 2·3 │ 3·3 │ 4·3 │ 6·1 │ 10·0 │
└─────────┴───────┴──────┴─────┴─────┴─────┴─────┴─────┴──────┘
┌──────┬──────┬──────┬───────┬──────────┐
│ │ │ │ │ 85 AND │
│ 45- │ 55- │ 65- │ 75- │ UPWARDS. │
├──────┼──────┼──────┼───────┼──────────┤
│ 20·0 │ 37·2 │ 69·8 │ 152·6 │ 300·3 │
│ │ │ │ │ │
│ 15·4 │ 29·8 │ 61·5 │ 142·6 │ 272·0 │
└──────┴──────┴──────┴───────┴──────────┘
Thus at ages over 5 and under 45 for males, and under 55 for females,
the death-rate is lower than is the total death-rate for all ages.
For females at all ages except from 5 to 15, the death-rate is lower
than for males. From the above statement it will be clear that a
considerable excess of women (as in a residential district with a
large number of domestic servants) or a considerable excess of either
sex at the ages of 15 to 45 (as in most large towns) in proportion to
the number living at other ages, would produce a lower total or crude
death-rate, which does not imply any truly more healthy condition than
that of another district, which is less favourably constituted so far
as the proportion of the sexes and the numbers living at different ages
are concerned. By a means of correction now to be described this source
of error can be eliminated. The method of obtaining the _factor for
correction_ can be best understood by an example. The annual death-rate
of England and Wales in 1881-90 was 19.15, and the death-rate at each
age-group is given in the following table:
┌─────────────────┬────────────────────────────┐
│ AGES. │ MEAN ANNUAL DEATH─RATE │
│ │ IN ENGLAND AND WALES │
│ │1881─90, PER 1,000 LIVING AT│
│ │ EACH GROUP OF AGES. │
├─────────────────┼────────────┬───────────────┤
│ │ _Males._ │ _Females._ │
│ _Under_ 5 │ 61.59 │ 51.95 │
│ 5 │ 5·35 │ 5·27 │
│ 10 │ 2·96 │ 3·11 │
│ 15 │ 4·33 │ 4·42 │
│ 20 │ 5·73 │ 5·54 │
│ 25 │ 7·78 │ 7·41 │
│ 35 │ 12·41 │ 10·61 │
│ 45 │ 19·36 │ 15·09 │
│ 55 │ 34·69 │ 28·45 │
│ 65 │ 70·39 │ 60·36 │
│ 75 _and upwards_│ 162.62 │ 147.98 │
└─────────────────┴────────────┴───────────────┘
┌──────────────────────┬───────────────────────┐
│ POPULATION │ CALCULATED │
│ OF HUDDERSFIELD IN │ NUMBER OF DEATHS │
│ 1891. │ IN HUDDERSFIELD. │
├─────────┬────────────┼──────────┬────────────┤
│_Males._ │ _Females._ │ _Males._ │ _Females._ │
│ 4,551 │ 4,785 │ 280 │ 249 │
│ 4,691 │ 5,081 │ 25 │ 27 │
│ 5,113 │ 5,165 │ 15 │ 16 │
├ 4,905 │ 5,549 │ 21 │ 25 │
│ 4,541 │ 5,461 │ 26 │ 30 │
│ 7,466 │ 8,834 │ 58 │ 65 │
│ 5,576 │ 6,265 │ 69 │ 66 │
│ 3,944 │ 4,649 │ 76 │ 70 │
│ 2,393 │ 3,017 │ 83 │ 86 │
│ 1,128 │ 1,590 │ 79 │ 96 │
│ 250 │ 466 │ 41 │ 69 │
├─────────┴────────────┼──────────┴────────────┤
Totals │44,558 50,862 │ 773 799 │
│ \──────/ │ \───────/ │
│ 95,420 │ 1,572 │
└──────────────────────┴───────────────────────┘
The population of Huddersfield at each of the corresponding periods
as given by the census of 1891, is also shown in this table, and in
the last column the number of male and female deaths that would occur
by applying the death-rates for England and Wales to the population
of Huddersfield are shewn. The total number of deaths thus calculated
is 1572 in a population of 95,420, and the total death-rate = 16·47
per 1000. This is the _standard death-rate_, _i.e._, the death-rate
at all ages calculated on the hypothesis that the rates at each of
12 age-periods in Huddersfield were the same as in England and Wales
during the ten years of the last intercensal period, viz. 19·15 in
1881-90.[13] But the standard death-rate of Huddersfield would
have been 19·15 instead of 16·47, were it not for the fact that the
distribution of age and sex in the Huddersfield population is more
favourable than in the country as a whole. Hence it must be increased
in the ratio of 19·15: 16·47, _i.e._, multiplied by the factor
19·15∕16·47 = 1·1627. When the crude or recorded death-rate for 1900 of
16·78 is multiplied by this factor we obtain the _corrected death-rate_
of 16·78 × 1·1627 = 19·51 per 1000, which is the correct figure to
compare with the death-rate of 18.31 for England and Wales in that
year. If the death-rate of England and Wales be stated as 1000, then
1000 × 1951∕1831 = 1066, is the _comparative mortality figure_ for
Huddersfield. Similarly in the year 1900 the comparative mortality
figure of London was 1093, of Croydon 831, of Norwich 919, while
that of Liverpool was 1539, of Salford 1541. In all the towns except
Plymouth and Norwich the corrected death-rate is higher than the crude
or recorded death-rate. This implies that, in all except these two
towns, the factor of correction is greater than unity.
This is a convenient point for briefly discussing the =relationship
between the birth-rate and death-rate=. The opinion is commonly held
that a high birth-rate is a direct cause of a high death-rate, owing to
the great mortality amongst infants. The table on page 340 shows that
the death-rate at ages under five is three times as high as at all ages
together, and it is therefore natural to suppose that a high birth-rate
by producing an excessive proportion of persons of tender years will
cause a high general death-rate. This might be so, if the birth-rate
were to remain high for only five years. But if the high birth-rate
continued longer, the proportion of the total population at ages of
low mortality would be increased, and the general death-rate would
be lowered. We have already seen that in nearly all the great towns,
in which the birth-rate is higher than in rural districts, the age
distribution of the population is more favourable to a low death-rate
than in rural districts; and their higher crude death-rate is made
still higher than that of rural districts when the necessary factor of
correction is applied.
The =Infantile Mortality= should be stated in terms of the infantile
population. This is more accurately assumed to be equal to the number
of births in the given year, than estimated from the number stated to
be under one year of age at the last census. The number of deaths under
one year of age per 1000 births was 163 for England and Wales in 1899,
being lowest in the agricultural counties and highest in manufacturing
counties. In the 33 great towns it averaged 172 in the year 1900,
ranging from 132 in Croydon, Huddersfield and Halifax to 236 per 1000
births in Preston. Of 1000 male children born in England and Wales
in 1881-90, the number surviving at the age of three months was 921,
at the age of six months 889, twelve months 839, while the number of
female children surviving one year of 1000 born was 869. In towns a
smaller number survive. Of the conditions causing this high infantile
mortality, ignorance and inexperience on the part of parents bear a
considerable part, especially as influencing the food and mode of
feeding. The death-rates at other age-groups beyond infancy are given
in the table on page 340. =Season= influences the death-rate. The third
quarter of the year has the lowest death-rate, unless the amount of
Epidemic Diarrhœa has been excessive. In the first quarter of the year,
the highest death-rate usually occurs. Mild winters and cool summers
both lower the mortality. The seasonal incidence of infectious diseases
need only be mentioned in passing.
=Density of Population= has important bearings on the death-rate.
Thus the urban districts in 1899 had a death-rate of 19·2 and the
rural of 16·3 per 1000 of population. Farr found that the death-rate
increased with the density of populations, not in direct proportion,
but in proportion to the 6th roots of the contrasted populations.
This rule does not now hold generally good. It is only after the
density has reached a certain degree of intensity that it begins
to exert an appreciable effect. Even then it is what is implied in
aggregation rather than the aggregation itself that is pernicious. In
particular, poverty is usually greater in densely populated districts
than elsewhere, with its accompaniments of deficient food and clothing
and bad housing. Hence the excess of phthisis in tenemented houses,
especially in houses with only three rooms. I have shown that the true
density that should be considered is the number of persons to each
room, not the number of persons on a given area (“The Vital Statistics
of the Peabody Buildings,” _Roy. Statist. Soc., Feb., 1891_).
=Occupation and Mortality.=—To obtain correct statistics showing the
influence of occupation on vitality, one must know the number and
age of those engaged in each industry, and the corresponding number
of deaths. A statement of the mean age at death of those engaged in
different occupations would be most fallacious (page 344). The best
plan is to restrict the statistics to men aged 25-65, and calculate
for these _death-rates in a standard population_, after the fashion
already described (page 340). By this means a “comparative mortality
figure” can be obtained. For all males it is 1000, for farmers 563,
teachers 603, lawyers 821, doctors 966, butchers 1096, plumbers 1120,
brewers 1427, innkeepers 1659, potters 1706, file-makers 1810. Speaking
generally, the occupations are most unhealthy in which there is most
exposure to dust, to the breathing of foul air, and to excessive
indulgence in alcoholic drinks (for further details see the author’s
_Elements of Vital Statistics_, page 169 _et seq._).
=Deaths from Various Causes.=—These may be stated in proportion to
total deaths from all causes, or in terms of the population. The
first plan must be adopted only when it is desired to ascertain the
proportional share of a given cause of death in the total mortality. In
1899, in England and Wales the diseases named in the first column of
the table (page 344), were the most prolific causes of deaths.
ENGLAND AND WALES, 1899.
DEATHS FROM VARIOUS CAUSES TO 10,000 DEATHS FROM ALL CAUSES.
_Bronchitis_ 880
_Phthisis_ 729
_Pneumonia_ 685
_Old age_ 541
_Diarrhœa_, _Dysentery_ 511
_Cancer_ 452
_Apoplexy_ 327
_Influenza_ 213
_Whooping cough_ 174
_Measles_ 172
_Diphtheria_ 160
_Enteric fever_ 108
_Scarlet fever_ 64
_Small-pox_ 3
The diseases in the second column are given in order to indicate their
proportional share of the total number of deaths.
The proper plan of stating the death-rate from a given disease is in
terms of the population, or better still subdivided into death-rates
from the disease for different age-groups as in the table on page
340, if the number of deaths is not too small to admit of this. The
importance of stating the death-rate for different age-groups is
greatest for such diseases as diarrhœa, whooping cough, and measles,
in which most of the deaths occur at ages under five. In the following
table are given the death-rates from the causes of death which are most
important, either from their magnitude, or because of their preventible
character:—
ENGLAND AND WALES, 1899.—DEATH-RATE PER 1,000 PERSONS LIVING.
_Small-pox_ ·005
_Measles_ ·32
_Scarlet fever_ ·12
_Influenza_ ·39
_Whooping cough_ ·32
_Diphtheria_ ·29
_Enteric fever_ ·20
_Typhus fever_ ·001
_Cholera_ ·04
_Diarrhœa_, _Dysentery_ ·94
_Intemperance_ ·09[14]
_Cancer_ ·83
_Phthisis_ 1·34
_Other tubercular diseases_ ·58
_Premature birth_ ·58
_Old age_ ·99
_Apoplexy_ ·60
_Convulsions_ ·57
_Valvular disease of heart_ ·38
_Bronchitis_ 1·61
_Pneumonia_ 1·26
_Gastro-enteritis_ ·61
_Bright’s disease_ ·29
_Accidents_ ·59
_Ill defined and not
specified causes_ ·73
——
_All causes_ +18·33+
=Determination of Longevity.= We have hitherto considered only
death-rates, _i.e._ the number dying each year out of each 1,000 of
population. The mean duration of life involves another aspect of the
same problem. Although nothing is more uncertain than the duration
of individual life, the duration of life for the entire community is
subject to so little variation that annuities and life assurance can
be made the subject of exact calculations. Of the tests employed to
measure the duration of human life the most commonly employed is the
=mean age at death=.[15]
sum of ages at death.
Mean age at death = ——————————-——————————-.
number of deaths.
This is a fair method of stating the average longevity of a particular
group of persons, if the group is sufficiently large to avoid the
possible error caused by paucity of data (page 349). But it would
be entirely unsafe to assume that by this means a safe standard of
comparison between two groups can be formed. Thus in 1890 it was
stated that the mean age at death of workmen was 29-30 years, of the
well-to-do classes 55-60 years. This statement throws no light on the
relative vitality of the two classes under comparison. The well-to-do
classes consist largely of those whose working days are past; and it
is as untrustworthy to compare their mean age at death with that of
workmen, as it would be to base any conclusion on the fact that mean
age at death of bishops is much higher than that of curates. The mean
age at death is lowest in countries with a high birth-rate. Hence it
would be very fallacious to compare the mean age at death in England
and France.
The =probable duration of life= (_vie probable_) is a term sometimes
employed to denote the age at which any number of children born into
the world will be reduced to one half. In practice it can only be
ascertained from a life-table.
The true mean duration of life or expectation of life can only be
ascertained from a =Life Table=, and this must therefore be briefly
described. This is the true _biometer_, of equal importance in all
inquiries connected with human life with the barometer or thermometer
and similar instruments employed in physical research. The Life Table
represents “a generation of individuals passing through time.” The
data required for its construction are the number and ages of the
living, and the number and ages of the dying, _i.e._ the data required
for ascertaining the death-rate for each year of life. Theoretically
the best plan for forming a Life Table would be to observe a million
children, all born on the same day, through life, entering in a column
(headed _l_{x}_) the number who remain alive at the end of each
successive year until all have died; and in a second column (headed
_d_{x}_) the number dying before the completion of each year of life.
This method is impracticable, and were it otherwise, the experience
would be obsolete before it could be utilised. The method employed in
constructing the national Life Tables for England is, without tracing
the history of individuals through life, to assume that the population
being given by the census returns and the death-rate for each age for
a given decennium being known, that the same death-rate will continue
during the remainder of the lives of the population included in the
census returns.
The total mean number living and the total number dying for a given
age-period are known. The mean chance (_p_{x}_) of living one year
during this age-period is found by the fraction
Population - ½ Deaths
———————————-———————————- = _p_{x}_
Population + ½ Deaths
It is usual to start with a million or 100,000 children at birth,
and to make a separate table for the proportionate number of males
and females at birth. Thus in Brighton in 1881-90 these were in the
proportion of 51,195 and 48,805. Starting with 51,195 male infants
at birth, and multiplying this number by ·84608, the probability of
surviving for one year, we obtain 51,195 × ·84608 = 43,315. For the
second year of life, the probability of surviving was ·93398; hence the
number of survivors is
43,315 × ·93398 = 40,452, and so on.
The general arrangement is shewn in the following example of a Life
Table, which only gives the data at or near the two extremes of life,
the intermediate figures having been omitted from considerations of
space.
BRIGHTON LIFE TABLE.—MALES.
(Based on the mortality of the 10 years 1881-90.)
┌────┬───────────┬───────────┬────────────────────┬────────────────┐
│AGE.│ DYING IN │ BORN AND │SUM OF THE NUMBER │ MEAN AFTER │
│ │ EACH YEAR │ SURVIVING │LIVING, OR YEARS OF │ LIFE-TIME │
│ │ OF LIFE. │ AT EACH │LIFE LIVED AT EACH │(EXPECTATION OF │
│ │ │ AGE. │AGE, _x_ + 1, AND │ LIFE) AT EACH │
│ │ │ │UPWARDS, TO THE LAST│ AGE. │
│ │ │ │AGE IN THE TABLE. │ │
│ │ │ │ │ │
│ x │ d{x} │ l{x} │ Σl{x}+1 │ e{x}º │
├────┼───────────┼───────────┼────────────────────┼────────────────┤
│ 0 │ 7,880 │ 51,195 │ 2,206,174 │ 43·59 │
│ │ │ │ │ │
│ 1 │ 2,863 │ 43,315 │ 2,162,859 │ 50·43 │
│ │ │ │ │ │
│ 2 │ 996 │ 40,452 │ 2,122,407 │ 52·96 │
│ │ │ │ │ │
│ 3 │ 733 │ 39,456 │ 2,082,951 │ 53·29 │
│ │ │ │ │ │
│ 4 │ 440 │ 38,723 │ 2,044,228 │ 53·29 │
│ │ │ │ │ │
│ ── │ ── │ ── │ ── │ ── │
│ │ │ │ │ │
│ ── │ ── │ ── │ ── │ ── │
│ │ │ │ │ │
│ 97 │ 12 │ 29 │ 43 │ 1·60 │
│ │ │ │ │ │
│ 98 │ 7 │ 17 │ 26 │ 1·53 │
│ │ │ │ │ │
│ 99 │ 4 │ 10 │ 16 │ 1·48 │
└────┴───────────┴───────────┴────────────────────┴────────────────┘
The 43,315 males surviving to the end of the first year of life out of
51,195 born will each have lived a complete year in the first year, or
among them 43,315 years. Similarly the 40,452 males will live among
them 40,452 further complete years, and so on, until all the males
started with become extinct at the age of 105. Evidently, therefore,
the total number of complete years lived by the 51,195 males started
with at birth will be
43,315 + 40,452 + 39,456 + 38,723 + ... + 10 + 6 + 4 + 3 + 2 + 1 =
2,206,174 years, this sum being obtained by adding together the numbers
living at each age beyond (_i.e._ below on this table) the age in
question right down to its last item. This number of years is lived by
51,195 males. Hence the number of complete years lived by, _i.e._ the
expectation of life of, each male
2,206,174
= ————-————- = 43·09 years.
51,195
This is the _curtate expectation of life_. It deals only with the
complete years of life, not taking into account that portion of
life-time lived by each person in the year of his death, which may
be assumed to be on an average half a year. Hence the _complete
expectation of life_ according to the above table is 43·59 years.
In the following table the expectation of life (complete) for various
towns and for England is given:—
LIFE TABLE.—EXPECTATION OF LIFE AT BIRTH.
_Male._ _Female._
English Life Table, 1838-54 (_Farr_) 39·91 41·85
„ „ 1871-80 (_Ogle_) 41·35 44·62
„ „ 1881-90 (_Tatham_) 43·66 47·18
London, 1881-90 (_Murphy_) 40·66 44·91
Brighton, 1881-90 (_Newsholme_) 43·59 49·25
Manchester City, 1881-90 (_Tatham_) 34·71 38·44
Glasgow, 1881-90 (_Chambers_) 35·18 37·70
Formulæ of varying degrees of accuracy have been devised for giving in
the absence of a Life Table an approximation to the expectation of life.
=Willich’s Formula= is as follows:—If _x_ = expectation of life, and
_a_ = present age, then _x_ = 2∕3 (80-_a_). Thus, at the age of 50
years the expectation of life, according to this formula, is 20 years.
By the English life-table for 1881-90 it was 18.82 for males, and 20·56
for females. =Farr’s formula= is based on the birth and death-rates. If
b = birth-rate and d = death-rate per unit of population, then
Expectation of life = (2∕3 × 1∕d) + (1∕3 × 1∕b).
Thus b for England and Wales, 1889-98 = 30·3∕1,000 = ·0303.
and d „ „ „ = 18·4∕1,000 = ·0184.
(2∕3 × 1∕·0303) + (1∕3 × 1∕·0184) = 47.2 years, as compared with the
expectation of life for 1881-90 shown in the above table.
In a life-table the number out of which one dies annually} are
the mean age at death} identical
and the expectation of life} in value
when the whole duration of life from birth to death is included in
the calculation. This is only true for a stationary or life-table
population, in which the number dying is assumed to be regularly
replaced by a corresponding number of persons of the same age.
=Life Capital.=—The life-tables now in use are those based on the
experience of 1881-90. The gain in any subsequent year, as in 1900,
may be ascertained as follows: the mean population and the death-rate
for each age-group as 0-5, 5-10, etc., are calculated. Then the mean
death-rate of the same community for 1881-90 is applied to this
population. By this means the “calculated number” of deaths in 1900 is
obtained. The difference between these numbers and the “actual number”
obtained from the death-registers, gives the gain or loss during the
year. Next multiply these differences by the mean expectation of
life for the corresponding groups of years. By adding the gains thus
ascertained and subtracting any losses, we obtain the net gain in
“life-capital” (Tatham) during the year 1900.
=Tests of the Health of a Community.= 1. The _general death-rate_ is
the test most commonly applied, and generally trusted. It has its
limitations in this respect. It may usually be trusted in comparing a
town or district for a single year with preceding years, as the age
and sex distribution of a given population only changes slowly. But
when comparison with other towns or districts is made, the possibility
that erroneous conclusions may be drawn becomes considerable. (_a_)
Before the death-rates of two districts can be compared, either this
comparison must be made by means of death-rates for age-groups (0-5,
5-10, ... 65-75, etc.) or the factors of correction, the method of
obtaining which is described on page 341, must be applied. (_b_) It
must be ensured that in the two compared districts, an equal amount of
correction has been made for deaths occurring in public institutions
and among visitors (page 340). (_c_) Even when the above precautions
are taken, it is conceivable that a town with a death-rate of 15 per
1,000 may really be as healthy as another with a death-rate of 12
per 1,000, though a statistical justification of this statement is a
difficult task.
Social conditions quite irrespective of the sanitary condition or the
natural salubrity of a district have an important influence on the
death-rate. Poverty and all that it connotes, necessarily involves a
higher death-rate than occurs among the well-to-do. Furthermore, the
domestic servants employed by the latter frequently die in districts
other than those in which they are employed, without any possibility of
the requisite correction being made.
2. _The zymotic death-rate_ is frequently quoted as a test of
sanitary condition. This is a death-rate based on the deaths from the
“seven chief zymotic diseases,” small-pox, measles, whooping-cough,
diphtheria, scarlet fever, fever (chiefly enteric), and diarrhœa. This
death-rate should be entirely discarded, the death-rate from each
infectious disease being separately stated. A high death-rate from
enteric fever would be a much more serious reflection on the health of
a town than a high death-rate for whooping-cough.
The death-rate from each of these diseases in London and in England in
1899 was as follows:—
DEATH-RATE IN 1899 PER 1,000 LIVING.
_England and Wales._ _London._
_Small-pox_ ·005 _nil_
_Measles_ ·32 ·47
_Scarlet fever_ ·12 ·08
_Diphtheria_ ·29 ·43
_Typhus_ ·001 _nil_
_Enteric fever_ ·20 ·18
_Whooping cough_ ·32 ·38
_Diarrhœa_ ·94 ·92
A statement of the death-rate from each of these diseases for a series
of years is a much more trustworthy test than a similar statement for
a single year, in which accidental causes may have caused a temporary
increase, or than a statement of the average result for a series of
years, which tends to conceal the epidemic variations of the disease
in question. The danger of such averages has been well exposed by
Chadwick in the remark that “a mean between the condition of Dives and
Lazarus tends to make it appear that after all Lazarus has not so much
to complain of.”
3. _The infantile mortality_ (page 342) is a delicate test of mixed
sanitary and social conditions, and stress may always be laid on it
from these standpoints. The importance of comparing death-rates at
other age-groups has already been explained.
4. The most delicate and exact method, if all the data are accurate and
complete, is to construct a _Life Table_, and ascertain the expectation
of life in comparison with that of other communities.
The preceding statistical tests of the salubrity of a community,
and any others that may be available, should all, when practicable,
be utilised; and it should always be remembered that these tests,
especially the general death-rate, are most trustworthy when
contrasting the experience of a community with its past experience, and
least trustworthy when contrasting its experience with that of others;
owing to the difficulty in the latter case of ensuring the avoidance of
error arising from _non ceteris paribus_.
=Statistical Fallacies.=—If “fallacies” be regarded as synonymous with
“errors,” clearly they may occur at every step. They may be classified
as errors of data, and errors of methods. The most important _errors
of data_ are erroneous estimates of population, and erroneous returns
of deaths, especially in the direction of exclusion of certain deaths
(page 340). Death-rates for short periods are relatively untrustworthy.
The erroneous use of the mean age at death as a test of longevity has
been mentioned (page 344). These are in part also _errors of methods_,
and numerous mixed examples are given below.
=Errors from Paucity of Data= frequently arise, the “fallacy of
small numbers,” a too hasty generalization, being the most common
fault in medical writings, especially in therapeutics. The degree of
approximation to the truth of a varying number of observations is
estimated by means of =Poisson’s formula=.
μ = total number of cases recorded in two groups.
m = number in one group.
n = number in the other group, so that μ = m + n.
The extent of variation in the proportion of each group to the whole
will vary within the proportions represented by—
m∕μ + 2√(2mn∕μ^3), and n∕μ - 2√(2mn∕μ^3)
The larger the number of the total observations (μ), the less will be
the value of 2√(2mn∕μ^3), and the less will be the limits of error in
the simple proportion m∕μ.
Thus, of 147 cases of enteric fever, 17 died, a fatality of 11·4 per
cent. The possible error is determined by the second half of the above
formula—
= 2√(2 × 17 × 130∕147^3) = 2√(4,420∕3,176,523) = ·0746.
_i.e._ the possibility of error = ·0746 to unity or 7·46 per cent. In
other words, in a second series of cases of enteric fever under the
same conditions as the above, the fatality may vary from 3·94 to 18·86
per cent., a vague result which indicates that the first series cannot
be regarded as establishing more than a _primá facie_ case in favour of
any special method of treatment that may have been adopted.
=Non ceteris paribus.=—The necessity that data to be compared shall be
collected on a uniform plan, and be of a strictly comparable nature,
is very frequently ignored. The conclusion that the administration of
a given antiseptic is a valuable means of treating enteric fever is
not demonstrated by the fact that the fatality in the series of cases
thus treated is 7 per cent., while in another series treated without
antiseptics it is 14 per cent., unless it is shown that the age and
other previous conditions of the patients in the two cases were not
widely different, and unless the series are sufficiently long to avoid
the fallacy due to paucity of data.
=Errors from the Composition of Rates.=—If the death-rate of A having
a population of 10,000 is 10 per 1000, and of B having a population
of 20,000 is 15 per 1000, the combined death-rate is not (10 + 15)∕2
= 12·5. To obtain the correct combined death-rate, the number of
deaths in A (=100) and in B (=300) must first be ascertained, and the
death-rate on a population of 30,000 in which 400 deaths occurred will
then be found to be _13·3 per 1000_.
=Errors from Stating Deaths in proportion to Total Deaths.=—There is
nothing erroneous _per se_ in stating the proportion of deaths at one
age as a ratio of the total deaths at all ages, or the deaths from one
cause as a ratio of the total deaths from all causes. It is a useful
and in fact the only method practicable when it is required to give the
proportion of one of these to the other. But beyond this, such a ratio
cannot be trusted. For instance, the proportion of fatal accidents
among male infants is 12·2, and among female infants 25·1 per cent. of
the total fatal accidents in the male and female sex respectively. But
it would be erroneous, if it were concluded from these figures that
female are more subject to fatal accidents than male infants. The only
conclusion that they justify is that at higher ages females are much
less subject to fatal accidents than males. In actual facts, for every
1000 infants born, only 2·9 female as against 3·1 males die under one
year of age as the result of accident.
Again, suppose the case of two towns, A and B. A with a population
of 10,000 has 150 annual deaths, of which 20 are caused by cancer;
the general death-rate therefore being 15, and the death-rate from
cancer 2·0 per 1000, while the deaths from cancer form 2∕15 of the
total deaths. B, with the same population as A, has 300 deaths, its
death-rate being 30 per 1000, and 40 deaths from cancer, its cancer
death-rate being 4·0 per 1000; while the proportion of the deaths from
cancer to the total deaths is 2∕15 as before. It is useful to know
in regard to each of these individual communities that cancer causes
2∕15 of its total mortality, but no comparison between the two is
practicable on this basis. The only proper comparison is between the
death-rate from cancer per 1000 of population in A and B, which shows
that it is twice as high in B as in A. A still more accurate method is
to ascertain the number of deaths from cancer, and the number living at
different age-groups, thus avoiding any errors due to variations in age
and sex distribution of population.
=Errors as to Averages.=—The most common of these results from
paucity of data (page 349). Note that the results obtained from an
average cannot be applied to a particular case. The mean duration or
expectation of life, obtained from a life-table, expresses with almost
mathematical certainty, the number of years of life of the members of
a community _taken one with another_, but is often not accurate when
applied to a single individual.
In _Army statistics_ errors have arisen by failure to comprehend what
is meant by the _average strength_ of a force. The statistics must
comprise the lives of a given number of persons as well as the deaths
occurring among them _for an entire year_, or allowance must be made in
this respect when required.
_Hospital statistics_ for similar reasons are frequently fallacious.
Thus death-rates have been frequently given per 100 occupied beds,
which are most misleading, as the frequency of succession of patients
as well as the nature of the patients’ complaints will vary greatly in
different hospitals. The only proper method of stating hospital-returns
is on the basis of the aggregate annual number of cases treated to a
termination. The cases should be further subdivided according to age
and sex and disease. _Average death-rates for epidemic diseases_ when
used to compare one community with another may give rise to erroneous
conclusions. This is inseparable from the nature of such diseases.
During the period under comparison, one town may happen to have,
say, three epidemics, and the other four; possibly if two or three
additional years had been added to the series, the place of the two
towns would have been reversed as regards their average death-rate from
the disease in question. The proper plan is to give the death-rates
from the epidemic disease for every year recorded, to draw a curve of
these death-rates for the two towns on the same scale, and to compare
the height, the variations of height, and the trend of the curve in
each instance.
INDEX.
A
Acarus Scabiei, 276
Achorion Schönleinii, 276
Acne, 161
Aerated Waters, 46
Ague (see Malaria)
Air—Bacteria in, 109, 121
Composition, Properties of, 100
Contagia and, 109, 114
Degree of Moisture of, 119, 128
Gaseous and Other Impurities of, 111
Examination of, 126
Moisture of, 234
In Soil, 221
Suspended Impurities of, 105
Temperature of, 119, 128
of Mountains, 228
Purification of, 129
Air-space, amount required, 142
Alcohol, 55
Amines process, 191
Ammonia—in Air, 101
in Water, 86
Amyloids, 7
Amylaceous Foods, 19
Anopheles (see Mosquito)
Anthrax, 274, 306
Anti-cyclones, 233
Antidiphtheritic Serum, 268, 299
Anti-syphonage, 174
Antill Trap, 180
Apjohn’s Formula, 242
Arnott’s Valve, 149
Arrowroot, 19
Arsenic—in Beer, 62
in Wall Papers, 214
in Clothing, 272
Artesian Wells, 71
Artificial Ventilation, 152
Relative Value, 154
Ascaris, 278
Ash-pits, 199
Aspect, 201
Atavism, 246
B
Bacteria, 273
Bacterial Methods, Sewage Treatment, 192
Ballard’s Researches, 303
Barley, 18
Barometers, 237
Barometric Pressure, 231
Baths, 262
Beaufort’s Scale, 243
Beef, 10
Beer, 61
Bell-trap, 180
Benham’s Gas Burners, 157
Berkefeld Filter, 98
Beverages, 46
Bilharzia Hæmatobia, 277
Birds, Flesh of, 11
Birth-rate, 339
Black Death, 1
Bonds, English, Flemish, 205
Borax and Boric Acid, 44
Boyle’s Mica Valve, 149
Bowels, Attention to, 248
Brandy, 63
Bread, brown and white, 17, 41
Bricks, 205
Broad Irrigation, 192
Burnett’s Solution, 327
Butter, 14
Buys Ballot’s Law, 232
C
Caffeine, 48
Calorigen Stove, 157
Carbohydrates, 6
Carbolic Acid as Disinfectant, 327
Carbon Filters, 97
Carbonic Acid—in Air, 102, 111
estimation of, 126
Carbonic Oxide, 112
Calorie, 32
Carpets, 218
Cement, 213
Cereal Foods, 15
Cesspools, 183
Cheese, 13
Chicory, 50
Chigoe, 277
Chlorides in Water, 81
Chlorine as Disinfectant, 324
Cholera, 92, 225, 302
Cisterns, 76
Clarke’s Process, 94
Soap Test, 79
Climate, 227
Closets, 168
Clothing, 265
Coal Gas, 115
Cocoa, 51
Cod Liver Oil, 14
Coffee, 50
Cols, 233
Comparative Mortality Figures, 342
Concrete, 207
Condiments, 45
Condy’s Fluid, 325
Conservancy Methods, 194
Constipation, 248
Constitution, 245
Consumption (see Tuberculosis)
Container, 169
Cooking, 339
Cooper’s Ventilators, 149
Corrosive Sublimate as Disinfectant, 327
Cotton, 270
Cream, 15
Cyclones, 232
Cysticercus Cellulosæ, 23, 279
D
D-Trap, 169
Damp, Cause of, 211
Damp-proof Course, 210
Death-rate, 2
Crude, 340
Corrected, 342
Zymotic, 297, 348
Decomposed Meat, 24
Demography, 335
Density of Population, 343
Destructors, 200
Dew Point, 241
Diarrhœa, Epidemic, 302
Diet, 29
Dietaries, 33
Diffusion, 129
Diphtheria, 225, 298
Diseased Animals, Meat of, 23
Disinfection, 324
Distillation, 94
Drainage, 166
of Soil, 226
Drains, 177
Examination of, 180
Drugs, 54
Dust in Air, 105
Dust-bins, 199
Dyspepsia, 28, 248
E
Earth-closets, 195
Eggs, 11
Ellison’s Bricks, 151
Endemic Diseases, 289
Enteric Fever, 91, 224, 300
Epidemic Diarrhœa, 26, 225, 302
Epidemic Diseases, 289
Erysipelas, 110, 305
Excreta, 165
Exercise, 249
Expectation of Life, 346
F
Farcy (see Glanders)
Farr’s Formula, 347
Fats, 6
Favus, 276
Fermented Drinks, 55
Filaria, 278
Filters, 97
Filtration, 95
Fire Grates, 159
Fish, 11
Dangers of, 26
Flax, 270
Fleas, 277
Flesh Food, 9
Floors, 217
Flour, 16
Flukes (see Trematoda)
Fomites, 299
Food, 4
Diseases due to, 23
Heat value of, 32
Preparation and Preservation of, 38, 43
Relation of, to Mechanical Work, 36
Variations from Climate, Age, &c, 29
Vegetable and Animal, 31
Forests and Climate, 229
Formalin., 44
and Formaldehyde as disinfectants, 326
Fortin’s Barometer, 238
Fruits, 21
Fuel, 161
Fungi, 20
G
Gaertner’s Bacillus, 25
Galton’s Stove, 155
Gas Stoves, 157, 161
Gelatin, 9
Gin, 63
Glanders, 304
Glaisher’s Tables, 241
Glucose, 21
Gluten, 15
Gout, 28, 59
Goux System, 194
Graveyards, Air of, 118
Green Vegetables, 20, 42
Ground-water, 222
Gully-trap, 167, 180
H
Habits, 247
Haffkine’s Cholera Vaccine, 228
Hardness of Water, 79, 90
Heat, kinds of, 159
Hendon Disease, 27
Heredity, 245
Hermite Process, 191
Hopper-closets, 170
Hot Water Supplies, 163
Pipes, 162
House Construction, 209
Drainage, 165
Materials of Construction of, 205
Position of, 201
Refuse, 198
Slops, 165
Humidity, absolute and relative 235
Measurement of, 240
Hydatids, 279
Hydrocarbons, 6
Hydrophobia, 305
Hygrometers, 101, 240
I
Idiosyncrasy, 246
Illuminants, 115
Immunity, 287
Incubation Periods, 287
Infantile Mortality, 342
Infective Diseases, 284
of Animals, 24
Infectious Diseases, Hospitals for, 320
Notification of, 338
Influenza, 309
Insects and Disease, 281
Intermittent Downward Filtration, 192
Iron in Water, 83
Isobars, 231
Isolation, 319
Isothermal Lines, 230
J
Jenner’s Discoveries, 293
K
Koch’s Postulates, 285
L
Latrines, 174
Laveran, 282
Lead in Water, 82, 90
Workers in, 108
Lice (see Pediculi)
Liebig’s Extract of Meat, 10
Life Capital, 347
Tables, 345
Linen, 270
Lysol as Disinfectant, 327
M
Macaroni, 17
Main Sewers, 183
Maize, 18
Malaria, 91, 224, 307
Mallein, 304
Malt, 18, 62
Malted Bread, 17
Margarine, 15
McKinnell’s Ventilator, 149
Metabolism, 6
Measles, 297
Meat, 9
Diseased, 24
Tinned, 25
Parasites in, 23
Meat Poisoning, 25
Metchnikoff’s Theory, 289
Meteorological Observations, 237
Metallo-keramic Joint, 177
Miasm, 285
Microbes (see Bacteria)
Microscoporon Audouini, 275
Milk, 12
and Disease, 26, 296, 299, 301
Boric Acid in, 44
Souring of, 274
and Tuberculosis, 311
Mineral Waters, 47
Mortar, 206
Mosquito, 282, 308
Moule’s Closet, 195
Mountain Climate, 228
Mutton, 10
N
Natural Ventilation, 147
Relative value, 154
Nematoda, 278
Nitrogen, 274
Nitrates in Water, 81
Nitrification, 192, 220
Nitrogenous Foods, 5
Notification of Consumption, 314
Infectious Diseases, 318, 338
Trade Diseases, 337
O
Oatmeal, 17
Obesity, 28
Occupation and Mortality, 343
Offensive Trades, 120
Oidium albicans, 275
Oils, 46
Onion, 20
Over-feeding, 28
Oxygen in Air, 100
Oxygen Absorbed, 86
Oxyuris, 278
Oysters and Disease, 291
Ozone, 101
P
Pan-closets, 169
Pandemics, 289
Parasites, 276
in Meat, 23
Pasteur-Chamberland Filter, 98
Pasteurization of Milk, 13, 312
Pediculi, 277
Personal Hygiene, 245, 257, 260
Pettenkofer’s Method, 126
Phagocytosis, 287
Phosphorus, in Food, 5
Workers with, 108
Phthisis, 225, 310
Piles, 248
Plaster, 212
Plague, 281, 305
Pneumatic System, Liernur, 183
Poisson’s Formula, 349
Population, Density of, 343
Estimation of, 336
Pork, 11
Porter-Clarke Process, 95
Portland Cement, 206
Potato, 20
Privy or Midden System, 196
Proof Spirit, 64
Proteids, 5
Propulsion, Ventilation by, 153
Puerperal Fever, 306
Q
Quarantine, 320
R
Rabies (see Hydrophobia)
Rainfall, 235
Rain Gauge, 242
Water, 67
Pipes, 166
Rats and Plague, 306
Registration of Births and Deaths, 337
Relapsing Fever, 28, 300
Respiration, 102, 113
Rest, 257
Rheumatic Fever, 225, 306
Rickets, 28
Ringworm, 275
Rivers, 72
Roasting, 38
Roofs, 208
Rum, 63
Rye, 18
S
Saccharomycetes, 275
Sago, 19
Salts as Food, 7
Saprophytes, 286
Scarlatina or Scarlet Fever, 296
Schools, Closure of, 322
Scott Moncrieff Process, 192
Scrofula, 316
Scurvy, 2, 27
Seasonal Incidence of Diseases, 289
Sea Relation to Climate, 229
Sebaceous Glands, 260
Semolina, 17
Septic-tank, 193
Sewage—Disposal of, 190
Dry and Wet Methods of Removal of, 197
Sewers, 183, 184
Air of, 117
Problems as to flow in, 187
Shell-fish and Disease, 291
Sheringham’s Valve, 151
Shone System, 186
Sinks, 167
Silk, 270
Sleep, 258
Slop-closets, 174
Small-pox, 2, 292
Smoke Nuisance, 160
Test, 181
Soap, 261
Soil, 219
Diseases in Relation to, 224
Drainage of, 226
Soil-pipe, 174
Spices, 46
Spirits, 63
Springs, 68
Starch, Detection of, 19
Starvation, 27
Statistical Fallacies, 349
Steam as Disinfectant, 329
Stoves, 157, 161
Streets, Width of, 203
Sugar, 21
Sulphuretted Hydrogen, 112
Sulphurous Acid (Disinfectant), 325
Summer Diarrhœa, 225
Sunshine Recorders, 243
Sweat Glands, 260
Sweating Sickness, 1
Sylvester’s Method, 150
Synoptic Map, 231
Syphonic Closet, 172
T
Tannin, 49
Tape-worms, 279
Tapioca, 19
Tea, 30, 47
Temperature of Rooms, 158
Tetanus, 304
Thermometers, Maximum and Minimum, 239
Thermometers, Dry and Wet Bulb, 240
Thrush, 275
Tight Lacing, 267
Tinea, 276
Tobacco, 54
Tobin’s Tubes, 152
Toxins, 286
Trades and Disease, 107, 118
Offensive, 120
Traps, 179
Trematoda, 277
Trichina Spiralis, 23
Trichophyton, 275
Trough-closets, 174
Tuberculin Test, 311
Tuberculosis, 309
Prevention of, 314
Tuberculous Meat, 24
Typhoid Fever (see Enteric Fever)
Typhus Fever, 300
V
V-shaped Depressions, 233
Vaccination, 293
Valve-closets, 170
Variola (see Small-pox)
Veal, 10
Vegetables, 20
Ventilation, 132
Methods of, 146
Problems as to, 137
By Propulsion, 153
Ventilation by Introduction of Warmed Air, 155
Of Mines, 156
Of Drains, 178
Vermicelli, 17
Vernier, 238
Vinegar, 46
Vital Statistics, 335
W
Wall-paper, 214
Walls of House, 210
Wanklyn’s Ammonia Process, 86
Warming of Houses, 159
Wash-out and Wash-down Closets, 172
Waste-pipes, 166
Water, 65
As food, 8
Analysis of, 84
Classification of supplies of, 73
Constant and Intermittent Services, 76
Enteric Fever and, 72
Hardness of, 79
Impurities of, 78, 89, 90
Sources of, 66
Storage and Delivery of, 74
in Soil, 222
Purification of, 94
Water-closets, 168
Water-gas, Carburetted, 115
Water-test of Drains, 182
Weather Forecasting, 234
Weissman on Heredity, 246
Wells, 69
Whiskey, 63
Whooping Cough, 298
Widal Reaction, 301
Willich’s Formula, 347
Windows, 216
Winds, 131, 230, 243
Wines, 62
Wool, 269
Wool-sorters’ Disease, 274
Work, Amount done, 252
Relation of Food to, 36
Wort, 62
Writers’ Palsy, 252
Y
Yellow Fever, 305
Z
Zygophyta, 275
FOOTNOTES:
[Footnote 1: While the addition of animal fat like margarine raises the
melting point, rape-seed oil and other vegetable oils lower it.]
[Footnote 2: The fat to be analysed is saponified with soda or potash,
and then the fatty acid set free by hydrochloric acid. If water be now
added, 11 or 12 per cent. of the fatty acid will be dissolved, if the
fat is butter; less than this if it is a mixture; and not more than 5
per cent. if no butter is present in the fat.]
[Footnote 3: Freshly made; of which 1 c.c. = ·00001 grm. of N₂O₃]
[Footnote 4: Made by dissolving ·395 grm. of KMnO₄ in 1,000 c.c. of
water. Each c.c. of this solution =·0001 grm. of oxygen available for
oxidation.]
[Footnote 5: Caused by the liberation of iodine. Thus—
K₂Mn₂O₈ + 8 H₂SO₄ + 10 KI = 6 K₂SO₄ + 2 MnSO₄ + 8 H₂O + 5 I₂.]
[Footnote 6: Of the strength of 1 grm. of crystalline sodium
thiosulphate to 1 litre of water.]
[Footnote 7: In practice one has frequently to be contented if the CO₂
does not exceed 1 part per 1000 of air; and if the room is clean and
free from dust, this higher limit may be accepted.]
[Footnote 8: The damp-proof course should have been shown close under
the plate carrying the floor joists.]
[Footnote 9: Some bacteria form in their interior minute _spores_, by
means of which they are able to resist ordinary destructive agents.
These spores again develope into bacteria.]
[Footnote 10: Furthermore, it is stated that when at rest on a plane
surface the Culex assumes a position with the axis of the body more
or less parallel to the surface; while the Anopheles, under the same
circumstances, has the axis of its body more or less at right angles to
the surface.]
[Footnote 11: This is diphtheria attacking the larynx]
[Footnote 12: From “Elements of Vital Statistics,” by A Newsholme.]
[Footnote 13: This was written before the figures for the period
1891-1900 were available; but the method adopted is the same,
substituting the death-rates, etc., for the later period.]
[Footnote 14: The death-returns greatly understate the actual
death-rate from this cause.]
[Footnote 15: There is no general agreement as to the exact sense in
which the words _average_ and _mean_ should be used. They are used here
interchangeably.]