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Sanitary institute
298
Abolishing Tuberculosis
trub~cHe~at~
Already the rate of diminution in the prevalence of phthisis is greater than that of leprosy when that disease began to decline. I t took at least two hundred years for leprosy to diminish to any appreciable extent ; but in sixty years there has been a decline in phthisis of at least two-thirds. When all our forces are brought fully into action, we may surely expect that at least as great a rate of decline will be continued ; and, in this case, another thirty years should see its vanishing point. We can hardly doubt ~hat the retreat will go on at an increasing speed. When all health authorities perform efficiently the several tasks which have now been set before them, when, by the means which have been mentioned, tuberculous cattle have been banished from our herds, when the general public have been fully instructed how to deal with tuberculous material, and when, by means of " open-air sanatoria " in connection with all our great towns, the existing consumptives and other tuberculous patients are provided with the requisite essentials for their cure, then m a y we hope for complete success.
SANITARY
INSTITUTE.
SOME P R E V A L E N T F A L L A C I E S I N V I T A L S T A T I S T I C S . * BY EDWARD F. WILLOUGHBY, M.D., D.P.H. IT is impossible for me in the limited time allowed on this occasion to touch on the fallacies incident to all popular discussions of such social and economic problems as those of the so-called depopulation of the rural districts, and migration to the towns, the distribution of wealth, and the growth or decline of pauperism, of over-population, emigration, and other industrial questions in their relations to demography. I must confine myself to pointing out a few of the most frequent and gravest mistakes arising from the abuse of statistics. Estimated populations, based on the assumption that the rate of increase observed in the last decennium is maintained in the present, lead to serious errors in the calculation of the death-rate and the presumed healthiness of the community. I f the estimated differ from the actual population by no more than 10 per cent. plus or minus, a supposed death-rate of 24 per 1,000 will represent a true rate of 26"4 or 21"6 respectively, and each successive census effects rude disillusions, Thus, in 1871 the population of Gosport was found to have been overestimated by 33 per cent., and that of Cambridge under-estimated by 16 per cent., their death-rates being identical instead of differing by 12 per cent. I n 1881, that of Kensington had been over-estimated by 26 per cent., and its vaunted death-rate of 15 per 1,000 was turned into the very ordinary 18"75. In 1891 the population of London was found to be, as Dr. Longstaff had predicted, a quarter of a million less than the Registrar-General's estimate. Constitution of Po~lation.--Sinee the end of the determination of the death-rate is to ascertain the accidental conditions, sanitary, social, or industrial, affecting the health of the people, it is necessary that essential conditions, over which we have no control, but which exert an influence on the death-rate, irrespective of those that are remediable, should be eliminated before any conclusions are drawn ; or, as logicians express it, that all the phenomena should be common except those which constitute the causes or the effects of the phenomenon that is Abstract of a paper read December, 1898.
~r~,
ls991
Some
Fallacies in Vital Statistics
299
the subject of inquiry. Foremost among these is the age and sex constitution of a population. Since the death-rate of children under 5 years is 63 per 1,000, of persons from 5 to 25 only 6 per 1,000, and of those from 25 to 45 years of age 10 per 1,000, it is evident that a preponderance of individuals of one or other of these age periods will greatly influence the death-rate even should all other conditions be identical; and, conversely, that if the age constitutions be the same, the influence of those remediable conditions that determine an excessive mortality will be seen in the death-rate. The decennial reports of the Registrar-General enable us thus to reduce the populations of every town or district to a common standard, thereby rendering them comparable. H e publishes the numbers of persons of each sex and within each age period, together with the death-rate for each sex and age for the country as a whole, and the sex and age constitution of the population of each town separately. From these data one is able to calculate for any place two death-rates besides the crude or " r e c o r d e d " rate, viz., the " s t a n d a r d rate," or that at which, constituted as they are, they ought to die if the conditions under which they lived were no better or worse than those of the country generally ; and the "corrected rate," or that at which, under existing co,editions, they would die if only the relative proportions of persons at each age-period did not differ from those of the nation taken as a whole. The standard represents an ideal presumably attainable in the present state of civilization, and therefore to be aimed a t ; the corrected rate exhibits the naked truth, stripped of the accidents by which it was concealed. One example, that of Manchester, will suffice to explain the meaning of these rates. In 1891 the crude or recorded death-rate was 28"67, the standard 19"09, and the corrected 31"95 ; the extremes of 32 and 19, representing the actual sanitary condition of the population and what it might be with no higher ideal than that of England generally, and the difference, 19,.5 per thousand, or 40 per cent. of the total mortality, indicates the amount that is preventible. Crude death-rates are determined far less by the sanitary conditions than by the ages of the people, and the aim of " correction" is to exclude this source of error. But there is in m a n y towns a disturbing factor that cannot be ~liminated, yet has not received the attention it deserves. I mean the presence of a large number of female servants, who, like all young unmarried women, tend to lower both the birth and death-rates, but, unlike others, may be said never to die at all, for if they seem likely to do so, they are at once sent to their homes, mostly out of the district, and their places are filled by others from elsewhere. Their influence on the death-rate is therefore the same as would be exerted by the presence of a like number of immortals, and is greatest where there is no considerable working-class population from which they might be drawn. Great public schools, universities and garrisons, act in like manner, but are not so apt to be overlooked. The mean age at death is of little practical value, since the same mean may be obtained from very different extremes. The mean duratio~ of life, as obtained by dividing the population by the mean annual number of deaths, is a fertile source of error. Thus, if 100 deaths occur annually in a population of 4,000--that is, 1 person in 40 dies every y e a r - - t h e death-rate is 25 per 1,000, and the mean duration of life is said to be 40 years. This, however, is true of a stationary population only, one in which the births equal the deaths, as in France, but most misleading where for two removed by death three are introduced by birth or immigration; so much so, that with the
300
S o m e Fallacies in Vital Statistics
[PublicHealth
highest birth-rate possible under the circumstances, the death-rate of 5 per 1,000 assumed by Sir. B. W. Richardson for his Hygeiopolis might imply a mean lifetime, not of 200 years, as was hastily asserted, but a little over the traditional threescore years and ten. The expressions, "excess of births over deaths," and " h i g h and low (general) death-rates," though convenient and, in the absence of better, indispensable, are, as Professor Ruata, of Perugia, points out, inaccurate and liable to misapprehension. The apparent excess of births is due to the increase in geometrical progression of actively reproductive individuals in the community ; and by a high death-rate we mean an undue proportion of premature and avoidable deaths, in the reduction of which preventive medicine has achieved its greatest triumphs---e.g., of a million children born, 95,000 more reach the age of 15, and 40,000 more that of 30, than in the last generation. Between 1860 and 1890 the mortality from scarlatina sank from 0"983 to 0"246 per 1,000, or as 4 : 1, from enteric fever from 0'850 to 0"180, or nearly 5 : 1; and from phthisis from 2"528 to 1"635, or 3 : 9.. Yet the waste of infant life is still appalling, 18 or 20 of 100 born dying in the great manufacturing towns, and 15 in England generally, in their first year, against 9 or 10 in Ireland and in Norway. But since everyone will die sooner or later, a reduction of the deaths in one age-period must be compensated by an increase in another, and the consummation of preventive medicine would be attained when the whole mortality should be concentrated in the last decade of human life. Already the mean lifetime has been extended by four or five years, but fewer, I believe, attain to extreme old age than formerly. Patriarchal longevity requires patriarchal conditions and habits, and centenarians cannot be numerous in the present strain and struggle of life. Our end will have been achieved when nearly all shall survive far into the period of useful activity, and those who reach a good old age shall retain their faculties and energies to the last days of their lives, senile decrepitude and imbecility being no longer known. Death-rates of infants, of children under 5, and of persons over 60, if they are to be of the smallest use, should always be based on the number of persons .living at each particular age, and in the case of infants under one year, on the births recorded. The proportion which the number of old people bears to the total population is no indication of the general longevity, being determined far more by the fertility of the marriages. I t is in this way that the French have been erroneously credited with a greater general longevity than the English, solely on account of their smaller families. The mortality from each of two diseases may be referred to as indicating the need of considering the age constitution of populations. Scarlet fever is a disease of childhood, 92 per cent. of the deaths occurring among children under ten years of age. Both in Berlin and in London such children constitute 25 per cent. of the populations, but in Paris 12'4 per cent. only. If, then, the mortality at all ages from this disease be 2"8 in Berlin and London, and 3"4 in Paris, the mortality among children under ten in Paris compared with that prevailing in each of the other two cities is as 2"3 to 1. Cancer, on the other hand, is scarcely known among those under the thirty-fifth year of life. If a population contain an excess of persons over this age, the cancer mortality at all ages might be high, although the incidence of the disease at the ages mentioned were not above the average. The natural increase of a .population depends not only on the number and fertility of the marriages, but on the age at which girls are married ;
~a~uary,1899j S o m e Fallacies in Vital Statistics
301
for while it is doubtful whether within certain limits this makes much difference in the number of children to a marriage, it is clear that the rate of increase of the population will be influenced by the intervals between successive generations. Thus, if the average age at which the girls m a r r y be 19, there will be 5, and if 24, then only 4 generations to a century, and the population will increase in like proportions, though all other conditions and factors be the same, recourse to artificial means for the limitation of families being uncalled for. If, on the other hand, there is a great demand for population, there is always a large reserve of marriageable and eligible persons of both sexes to be drawn on even to the extent of doubling the birth-rate. In determining the fertility of women or the number of children to a family, the births should be calculated not on the number of marriages, but of women who have married, for the procreative period of the female being limited, a widow who marries again does not make a fresh start, but is in the same position, if still young, as she would have been had her first husband not died, and if old as if she had remained a widow. The comparative healthiness of occupations is a question bristling with fallacies, the common practice of taking the mean age at death as an indication of the healthiness of an employment being delusive in the extreme. The only proper method is that of Dr. Ogle, viz., to compare ~he death-rate per thousand living with that of the general population of the same age and sex. A like fallacy is involved in the assumption that married life is in itself more conducive to health and longevity than is celibacy. No doubt bachelors are more prone to irregular habits, but many persons of both sexes abstain from marriage on account of their ill-health or physical defects, and are not unhealthy because they remain single. The influence of the marriage market on female labour and employment is such as to deprive the mean age at death of all significance, and even to falsify m a n y conclusions drawn by Dr. Ogle's method, for very few women continue to follow the same occupation for the twenty years required, much less throughout their lives. Domestic servants, shop-girls, and female clerks usually marry after a few years. Servants especially rarely die as such, and it is only as mill or factory hands that women to any great extent keep to the same work after marriage as before. I would not underrate the ill results of sedentary employment in overcrowded rooms, but I do believe that the very high mortality, especially from phthisis, among needle-women, etc., may be in large part explained by the removal through marriage of the healthier and comelier girls. A very prevalent source of error in questions of this kind is the fallacy of ascribing to one particular cause, perhaps a real and powerful factor, but still only one among others not less powerful, the whole effect of a plurality of causes. So, too, in determining, e.g., the influence of heredity in the production of phthisis, of cancer or leprosy, or of a certain milk supply in the spread of a fever, much more than the mere concurrence or succession of two phenomena is required to prove their relation as cause and effect. In every such investigation the inductive methods of agreement, of difference, and of concomitant variations, must be worked through, and the possibility of a plurality of causes should not be lost sight of. All class mortalities, death-rates at certain ages and the like, must
302
S o m e Fallacies in Vital Statistics
~P~l,n~~e~a~
be calculated on the population living at those ages or belonging to the particular class, but there are some in which the sources of error and elements of uncertainty are such as to suggest the description of " i n determinate and impossible" death-rates, represented respectively by those of armies and of hospitals. To throw together under the head of "foreign service" the mortalities of troops in B u r m a and in Canada, and to compare the rates with those at home, is obviously unfair. Besides, no soldier can die on the roll of his regiment, save from violence, accident, or acute disease, unless through the neglect of the authorities to invalid him in time, and the only trustworthy indication of the sanitary condition of an army is the percentage of deaths and invaliding from all causes among men of like ages and periods of service. I f a corps or a station is to be compared, not with itself at a former time, but with others, their conditions must be as nearly as possible the same, except in respect of that the influence of which, be it climate, quarters, age, or anything else, it is desired to determine. In the case of hospitals, and to a less extent of prisons, the difficulties are well-nigh insuperable. The death-rates must be calculated not on the average strength, but on the number of admissions in the year. But the circumstances of hospitals as regards the nature and gravity of the cases, the proportion of medical to surgical beds, the demand for admissions, and consequent length of time during which a patient is allowed to remain, are so diverse that comparisons are rarely possible. The only legitimate comparisons are between those in which all conditions, save the one in question, are practically identical. Such, perhaps, would be maternity or fever hospitals where patients suffering in similar manners are retained till recovery or death, the same hospital in successive years or periods, and hospitals of the same character, situated in the same locality and among the same population. Iv these the results of the practice or the rejection of serum-therapy or antiseptic methods, the adoption of the pavilion system or the retention of the solid block, or other striking contrast, may fairly be accepted as the determinant factor of markedly divergent mortalities.
ANALYTICAL NOTES. G. A. LE ROY. (Zeit. /~r Sawdust can be detected in common descriptions of flour by means of an alcoholic solution of phloroglucinol strongly acidified with phosphoric acid. On gently warming, the particles of sawdust acquire a strong carmine-red colour, whereas the bran particles of the cereals are at first scarcely affected at all. A CURIOUSMEAT-PREsERVATIVE. ALFREDC. CHAPMAN,F.I.C. Analyst, 1898, 309. The author's analysis of a sample of an antiseptic solution intended for preservation of meat revealed the following substances: Aluminium sulphate, sodium chloride, sodium nitrate, sulphurous acid, chloral hydrate, benzoic acid, and a small quantity of iodine, apparently existing as hydriodic acid. The alum was evidently intended to exert its astringent effect upon the fibre of the meat, whilst the remaining constituents (with the exception, perhaps, of the chloral) are, of course, DETECTION OF SAWDUST IN FLOUR.
Untersuch. der Nahr. and Genussmittel, 1898, 505.)
Abolishing Tuberculosis
trub~cHe~at~
Already the rate of diminution in the prevalence of phthisis is greater than that of leprosy when that disease began to decline. I t took at least two hundred years for leprosy to diminish to any appreciable extent ; but in sixty years there has been a decline in phthisis of at least two-thirds. When all our forces are brought fully into action, we may surely expect that at least as great a rate of decline will be continued ; and, in this case, another thirty years should see its vanishing point. We can hardly doubt ~hat the retreat will go on at an increasing speed. When all health authorities perform efficiently the several tasks which have now been set before them, when, by the means which have been mentioned, tuberculous cattle have been banished from our herds, when the general public have been fully instructed how to deal with tuberculous material, and when, by means of " open-air sanatoria " in connection with all our great towns, the existing consumptives and other tuberculous patients are provided with the requisite essentials for their cure, then m a y we hope for complete success.
SANITARY
INSTITUTE.
SOME P R E V A L E N T F A L L A C I E S I N V I T A L S T A T I S T I C S . * BY EDWARD F. WILLOUGHBY, M.D., D.P.H. IT is impossible for me in the limited time allowed on this occasion to touch on the fallacies incident to all popular discussions of such social and economic problems as those of the so-called depopulation of the rural districts, and migration to the towns, the distribution of wealth, and the growth or decline of pauperism, of over-population, emigration, and other industrial questions in their relations to demography. I must confine myself to pointing out a few of the most frequent and gravest mistakes arising from the abuse of statistics. Estimated populations, based on the assumption that the rate of increase observed in the last decennium is maintained in the present, lead to serious errors in the calculation of the death-rate and the presumed healthiness of the community. I f the estimated differ from the actual population by no more than 10 per cent. plus or minus, a supposed death-rate of 24 per 1,000 will represent a true rate of 26"4 or 21"6 respectively, and each successive census effects rude disillusions, Thus, in 1871 the population of Gosport was found to have been overestimated by 33 per cent., and that of Cambridge under-estimated by 16 per cent., their death-rates being identical instead of differing by 12 per cent. I n 1881, that of Kensington had been over-estimated by 26 per cent., and its vaunted death-rate of 15 per 1,000 was turned into the very ordinary 18"75. In 1891 the population of London was found to be, as Dr. Longstaff had predicted, a quarter of a million less than the Registrar-General's estimate. Constitution of Po~lation.--Sinee the end of the determination of the death-rate is to ascertain the accidental conditions, sanitary, social, or industrial, affecting the health of the people, it is necessary that essential conditions, over which we have no control, but which exert an influence on the death-rate, irrespective of those that are remediable, should be eliminated before any conclusions are drawn ; or, as logicians express it, that all the phenomena should be common except those which constitute the causes or the effects of the phenomenon that is Abstract of a paper read December, 1898.
~r~,
ls991
Some
Fallacies in Vital Statistics
299
the subject of inquiry. Foremost among these is the age and sex constitution of a population. Since the death-rate of children under 5 years is 63 per 1,000, of persons from 5 to 25 only 6 per 1,000, and of those from 25 to 45 years of age 10 per 1,000, it is evident that a preponderance of individuals of one or other of these age periods will greatly influence the death-rate even should all other conditions be identical; and, conversely, that if the age constitutions be the same, the influence of those remediable conditions that determine an excessive mortality will be seen in the death-rate. The decennial reports of the Registrar-General enable us thus to reduce the populations of every town or district to a common standard, thereby rendering them comparable. H e publishes the numbers of persons of each sex and within each age period, together with the death-rate for each sex and age for the country as a whole, and the sex and age constitution of the population of each town separately. From these data one is able to calculate for any place two death-rates besides the crude or " r e c o r d e d " rate, viz., the " s t a n d a r d rate," or that at which, constituted as they are, they ought to die if the conditions under which they lived were no better or worse than those of the country generally ; and the "corrected rate," or that at which, under existing co,editions, they would die if only the relative proportions of persons at each age-period did not differ from those of the nation taken as a whole. The standard represents an ideal presumably attainable in the present state of civilization, and therefore to be aimed a t ; the corrected rate exhibits the naked truth, stripped of the accidents by which it was concealed. One example, that of Manchester, will suffice to explain the meaning of these rates. In 1891 the crude or recorded death-rate was 28"67, the standard 19"09, and the corrected 31"95 ; the extremes of 32 and 19, representing the actual sanitary condition of the population and what it might be with no higher ideal than that of England generally, and the difference, 19,.5 per thousand, or 40 per cent. of the total mortality, indicates the amount that is preventible. Crude death-rates are determined far less by the sanitary conditions than by the ages of the people, and the aim of " correction" is to exclude this source of error. But there is in m a n y towns a disturbing factor that cannot be ~liminated, yet has not received the attention it deserves. I mean the presence of a large number of female servants, who, like all young unmarried women, tend to lower both the birth and death-rates, but, unlike others, may be said never to die at all, for if they seem likely to do so, they are at once sent to their homes, mostly out of the district, and their places are filled by others from elsewhere. Their influence on the death-rate is therefore the same as would be exerted by the presence of a like number of immortals, and is greatest where there is no considerable working-class population from which they might be drawn. Great public schools, universities and garrisons, act in like manner, but are not so apt to be overlooked. The mean age at death is of little practical value, since the same mean may be obtained from very different extremes. The mean duratio~ of life, as obtained by dividing the population by the mean annual number of deaths, is a fertile source of error. Thus, if 100 deaths occur annually in a population of 4,000--that is, 1 person in 40 dies every y e a r - - t h e death-rate is 25 per 1,000, and the mean duration of life is said to be 40 years. This, however, is true of a stationary population only, one in which the births equal the deaths, as in France, but most misleading where for two removed by death three are introduced by birth or immigration; so much so, that with the
300
S o m e Fallacies in Vital Statistics
[PublicHealth
highest birth-rate possible under the circumstances, the death-rate of 5 per 1,000 assumed by Sir. B. W. Richardson for his Hygeiopolis might imply a mean lifetime, not of 200 years, as was hastily asserted, but a little over the traditional threescore years and ten. The expressions, "excess of births over deaths," and " h i g h and low (general) death-rates," though convenient and, in the absence of better, indispensable, are, as Professor Ruata, of Perugia, points out, inaccurate and liable to misapprehension. The apparent excess of births is due to the increase in geometrical progression of actively reproductive individuals in the community ; and by a high death-rate we mean an undue proportion of premature and avoidable deaths, in the reduction of which preventive medicine has achieved its greatest triumphs---e.g., of a million children born, 95,000 more reach the age of 15, and 40,000 more that of 30, than in the last generation. Between 1860 and 1890 the mortality from scarlatina sank from 0"983 to 0"246 per 1,000, or as 4 : 1, from enteric fever from 0'850 to 0"180, or nearly 5 : 1; and from phthisis from 2"528 to 1"635, or 3 : 9.. Yet the waste of infant life is still appalling, 18 or 20 of 100 born dying in the great manufacturing towns, and 15 in England generally, in their first year, against 9 or 10 in Ireland and in Norway. But since everyone will die sooner or later, a reduction of the deaths in one age-period must be compensated by an increase in another, and the consummation of preventive medicine would be attained when the whole mortality should be concentrated in the last decade of human life. Already the mean lifetime has been extended by four or five years, but fewer, I believe, attain to extreme old age than formerly. Patriarchal longevity requires patriarchal conditions and habits, and centenarians cannot be numerous in the present strain and struggle of life. Our end will have been achieved when nearly all shall survive far into the period of useful activity, and those who reach a good old age shall retain their faculties and energies to the last days of their lives, senile decrepitude and imbecility being no longer known. Death-rates of infants, of children under 5, and of persons over 60, if they are to be of the smallest use, should always be based on the number of persons .living at each particular age, and in the case of infants under one year, on the births recorded. The proportion which the number of old people bears to the total population is no indication of the general longevity, being determined far more by the fertility of the marriages. I t is in this way that the French have been erroneously credited with a greater general longevity than the English, solely on account of their smaller families. The mortality from each of two diseases may be referred to as indicating the need of considering the age constitution of populations. Scarlet fever is a disease of childhood, 92 per cent. of the deaths occurring among children under ten years of age. Both in Berlin and in London such children constitute 25 per cent. of the populations, but in Paris 12'4 per cent. only. If, then, the mortality at all ages from this disease be 2"8 in Berlin and London, and 3"4 in Paris, the mortality among children under ten in Paris compared with that prevailing in each of the other two cities is as 2"3 to 1. Cancer, on the other hand, is scarcely known among those under the thirty-fifth year of life. If a population contain an excess of persons over this age, the cancer mortality at all ages might be high, although the incidence of the disease at the ages mentioned were not above the average. The natural increase of a .population depends not only on the number and fertility of the marriages, but on the age at which girls are married ;
~a~uary,1899j S o m e Fallacies in Vital Statistics
301
for while it is doubtful whether within certain limits this makes much difference in the number of children to a marriage, it is clear that the rate of increase of the population will be influenced by the intervals between successive generations. Thus, if the average age at which the girls m a r r y be 19, there will be 5, and if 24, then only 4 generations to a century, and the population will increase in like proportions, though all other conditions and factors be the same, recourse to artificial means for the limitation of families being uncalled for. If, on the other hand, there is a great demand for population, there is always a large reserve of marriageable and eligible persons of both sexes to be drawn on even to the extent of doubling the birth-rate. In determining the fertility of women or the number of children to a family, the births should be calculated not on the number of marriages, but of women who have married, for the procreative period of the female being limited, a widow who marries again does not make a fresh start, but is in the same position, if still young, as she would have been had her first husband not died, and if old as if she had remained a widow. The comparative healthiness of occupations is a question bristling with fallacies, the common practice of taking the mean age at death as an indication of the healthiness of an employment being delusive in the extreme. The only proper method is that of Dr. Ogle, viz., to compare ~he death-rate per thousand living with that of the general population of the same age and sex. A like fallacy is involved in the assumption that married life is in itself more conducive to health and longevity than is celibacy. No doubt bachelors are more prone to irregular habits, but many persons of both sexes abstain from marriage on account of their ill-health or physical defects, and are not unhealthy because they remain single. The influence of the marriage market on female labour and employment is such as to deprive the mean age at death of all significance, and even to falsify m a n y conclusions drawn by Dr. Ogle's method, for very few women continue to follow the same occupation for the twenty years required, much less throughout their lives. Domestic servants, shop-girls, and female clerks usually marry after a few years. Servants especially rarely die as such, and it is only as mill or factory hands that women to any great extent keep to the same work after marriage as before. I would not underrate the ill results of sedentary employment in overcrowded rooms, but I do believe that the very high mortality, especially from phthisis, among needle-women, etc., may be in large part explained by the removal through marriage of the healthier and comelier girls. A very prevalent source of error in questions of this kind is the fallacy of ascribing to one particular cause, perhaps a real and powerful factor, but still only one among others not less powerful, the whole effect of a plurality of causes. So, too, in determining, e.g., the influence of heredity in the production of phthisis, of cancer or leprosy, or of a certain milk supply in the spread of a fever, much more than the mere concurrence or succession of two phenomena is required to prove their relation as cause and effect. In every such investigation the inductive methods of agreement, of difference, and of concomitant variations, must be worked through, and the possibility of a plurality of causes should not be lost sight of. All class mortalities, death-rates at certain ages and the like, must
302
S o m e Fallacies in Vital Statistics
~P~l,n~~e~a~
be calculated on the population living at those ages or belonging to the particular class, but there are some in which the sources of error and elements of uncertainty are such as to suggest the description of " i n determinate and impossible" death-rates, represented respectively by those of armies and of hospitals. To throw together under the head of "foreign service" the mortalities of troops in B u r m a and in Canada, and to compare the rates with those at home, is obviously unfair. Besides, no soldier can die on the roll of his regiment, save from violence, accident, or acute disease, unless through the neglect of the authorities to invalid him in time, and the only trustworthy indication of the sanitary condition of an army is the percentage of deaths and invaliding from all causes among men of like ages and periods of service. I f a corps or a station is to be compared, not with itself at a former time, but with others, their conditions must be as nearly as possible the same, except in respect of that the influence of which, be it climate, quarters, age, or anything else, it is desired to determine. In the case of hospitals, and to a less extent of prisons, the difficulties are well-nigh insuperable. The death-rates must be calculated not on the average strength, but on the number of admissions in the year. But the circumstances of hospitals as regards the nature and gravity of the cases, the proportion of medical to surgical beds, the demand for admissions, and consequent length of time during which a patient is allowed to remain, are so diverse that comparisons are rarely possible. The only legitimate comparisons are between those in which all conditions, save the one in question, are practically identical. Such, perhaps, would be maternity or fever hospitals where patients suffering in similar manners are retained till recovery or death, the same hospital in successive years or periods, and hospitals of the same character, situated in the same locality and among the same population. Iv these the results of the practice or the rejection of serum-therapy or antiseptic methods, the adoption of the pavilion system or the retention of the solid block, or other striking contrast, may fairly be accepted as the determinant factor of markedly divergent mortalities.
ANALYTICAL NOTES. G. A. LE ROY. (Zeit. /~r Sawdust can be detected in common descriptions of flour by means of an alcoholic solution of phloroglucinol strongly acidified with phosphoric acid. On gently warming, the particles of sawdust acquire a strong carmine-red colour, whereas the bran particles of the cereals are at first scarcely affected at all. A CURIOUSMEAT-PREsERVATIVE. ALFREDC. CHAPMAN,F.I.C. Analyst, 1898, 309. The author's analysis of a sample of an antiseptic solution intended for preservation of meat revealed the following substances: Aluminium sulphate, sodium chloride, sodium nitrate, sulphurous acid, chloral hydrate, benzoic acid, and a small quantity of iodine, apparently existing as hydriodic acid. The alum was evidently intended to exert its astringent effect upon the fibre of the meat, whilst the remaining constituents (with the exception, perhaps, of the chloral) are, of course, DETECTION OF SAWDUST IN FLOUR.
Untersuch. der Nahr. and Genussmittel, 1898, 505.)