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THE IMPROVEMENT OF MORTALITY-RATES
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unexceptionable ; but the retort is also unexceptionable-namely, that his table does not tell us what most people are interested to know-what is likely to happen to them. Out of official hours, some actuaries (especially, we think, some Italian writers) have toyed with the idea of current life THE tables-i.e., of constructing tables in which the rates of mortality at advancing ages are based on advancing secular experience. KERMAOK, LONDON:SATURDAY, MARCH 31, 1934 McKErrDRacA, and McKiNLAY point out a hopeful way of trying to do what we all wish to have done. In view of their results, it does not seem quite so THE IMPROVEMENT OF MORTALITY-RATES chimerical as it once did to suppose that we might
LANCET
life table which would tell us what expectation of life " of men now aged, say, 40 really is. Naturally, as they point out, much more detailed analysis will be required before anything could come of the proposal, but they have suggested a method, and in language all intelligent readers can understand. How far their explanation-namely, that environmental factors up to the age of 15 are of overriding importance-is acceptable cannot be determined. Of course some will point to the historical fact that in industrial life the legislature intervened to safeguard the children before any protection was given to adults. It is, however, very difficult to propound a plausible working hypothesis of delayed environmental reforms, passing from age-group to age-group, which will adequately account for the results. It is hardly necessary to add that the authors do not suggest that environmental factors cannot influence rates of mortality at later ages ; their data are derived from countries and epochs in which (if we exclude war periods) on the whole the conditions of life at all ages have construct
ELSEWHERE in thjs issue we print a paper by Dr. KERMACK, Colonel McKENDBiCE, and Dr. McKlNLAY which will interest a circle of readers beyond the students of mathematical and statistical problems to whom the three authorsare already well known. It shows that if the rates of mortality of England and Wales in decennial agegroups are expressed as a percentage of the rates obtaining at a particular previous epoch and arranged on a chess-board in which rows correspond to secular time and columns to life time (see p. 699, Table II.) the result is that the entries in the diagonals are approximately equal. For instance, when expressed as a percentage of the rate prevailing in 1841-50, the rate of mortality in the age-group 5-15 in 1861-70 was 87, the rate of mortality in the age-group 15-25 in 1871-80 was 75, the rate of mortality in the age-group 25-35 in 1881-90 was 74, the rate of mortality in the age-group 35-45 in 1891-1900 was 81, and, proceeding thus, we have 84, 84, and 82, the last figure being the rate of mortality in the age-group 65-75 prevailing in the decennium 1921-30, expressed as a percentage of the corresponding rate in 1841-50. A similar rule is found to hold for Scottish experience. The longer secular record of mortality in Sweden appeared to be recalcitrant, but if a section of the table (from 1855 onwards) is omitted a similar trend can be discerned. The authors are far too well versed in the intricacies of statistical problems to be dogmatic in their interpretation of these results, but their paper should stimulate research in many directions. Probably some of our unmathematical readers who, declining to be terrified by a repulsive symbolism and such vaguely terrifying phrases as <
"
complete expectation
tion of
of
life," " curtate
expecta-
life," and so on, have discovered what those portentous documents the National Life Tables really mean, have recalled a line in Horace concerning the obstetrics of mountains. For the last English Life Table does not tell us how the generation in being in 1921-23 will die out, but how it would die out if the rates of mortality prevailing in every age-group in those three years were never to change. And even in these pessimistic days, professional esprit de corps will hardly .allow us to believe that no improvement in rates of mortality in any age-groups is possible. The answer of an actuary to any such criticism is that he is an arithmetician not a prophet, and the answer is
a
the "
improved. We hope
_
that the discussion initiated by this valuable paper will lead to further investigation of the whole subject.
THE CONTROL OF THE BLADDER WE have already referredto an investigation by Dr. D. DENNY-BROwN and Dr. E. GRABMB ROBERTSON into the control of micturition by the normal subject. Their important work has now been extended2 to patients with two types of lesion -destruction of the sacral roots of the spinal cord, and complete transection of the cord in or above the lumbar region, the cord being intact below the section. The effect of the first lesion is to destroy the central connexions of the pelvic nerves (nervi erigentes) which terminate peripherally in the vesical plexus, and of the pudic nerves which supply the external sphincter and other perineal muscles. The second lesion leaves these central connexions intact, but cuts off all communication with higher centres. The influence of the hypogastric nerves, originating in the lower thoracic and first lumbar segments and passing via the inferior mesenteric ganglion to the vesical plexus, is so slight that it may be neglected in this summary. 1 THE
LANCET, 1933, ii., 605. 2 Brain, 1933, lvi., 397.
unexceptionable ; but the retort is also unexceptionable-namely, that his table does not tell us what most people are interested to know-what is likely to happen to them. Out of official hours, some actuaries (especially, we think, some Italian writers) have toyed with the idea of current life THE tables-i.e., of constructing tables in which the rates of mortality at advancing ages are based on advancing secular experience. KERMAOK, LONDON:SATURDAY, MARCH 31, 1934 McKErrDRacA, and McKiNLAY point out a hopeful way of trying to do what we all wish to have done. In view of their results, it does not seem quite so THE IMPROVEMENT OF MORTALITY-RATES chimerical as it once did to suppose that we might
LANCET
life table which would tell us what expectation of life " of men now aged, say, 40 really is. Naturally, as they point out, much more detailed analysis will be required before anything could come of the proposal, but they have suggested a method, and in language all intelligent readers can understand. How far their explanation-namely, that environmental factors up to the age of 15 are of overriding importance-is acceptable cannot be determined. Of course some will point to the historical fact that in industrial life the legislature intervened to safeguard the children before any protection was given to adults. It is, however, very difficult to propound a plausible working hypothesis of delayed environmental reforms, passing from age-group to age-group, which will adequately account for the results. It is hardly necessary to add that the authors do not suggest that environmental factors cannot influence rates of mortality at later ages ; their data are derived from countries and epochs in which (if we exclude war periods) on the whole the conditions of life at all ages have construct
ELSEWHERE in thjs issue we print a paper by Dr. KERMACK, Colonel McKENDBiCE, and Dr. McKlNLAY which will interest a circle of readers beyond the students of mathematical and statistical problems to whom the three authorsare already well known. It shows that if the rates of mortality of England and Wales in decennial agegroups are expressed as a percentage of the rates obtaining at a particular previous epoch and arranged on a chess-board in which rows correspond to secular time and columns to life time (see p. 699, Table II.) the result is that the entries in the diagonals are approximately equal. For instance, when expressed as a percentage of the rate prevailing in 1841-50, the rate of mortality in the age-group 5-15 in 1861-70 was 87, the rate of mortality in the age-group 15-25 in 1871-80 was 75, the rate of mortality in the age-group 25-35 in 1881-90 was 74, the rate of mortality in the age-group 35-45 in 1891-1900 was 81, and, proceeding thus, we have 84, 84, and 82, the last figure being the rate of mortality in the age-group 65-75 prevailing in the decennium 1921-30, expressed as a percentage of the corresponding rate in 1841-50. A similar rule is found to hold for Scottish experience. The longer secular record of mortality in Sweden appeared to be recalcitrant, but if a section of the table (from 1855 onwards) is omitted a similar trend can be discerned. The authors are far too well versed in the intricacies of statistical problems to be dogmatic in their interpretation of these results, but their paper should stimulate research in many directions. Probably some of our unmathematical readers who, declining to be terrified by a repulsive symbolism and such vaguely terrifying phrases as <
"
complete expectation
tion of
of
life," " curtate
expecta-
life," and so on, have discovered what those portentous documents the National Life Tables really mean, have recalled a line in Horace concerning the obstetrics of mountains. For the last English Life Table does not tell us how the generation in being in 1921-23 will die out, but how it would die out if the rates of mortality prevailing in every age-group in those three years were never to change. And even in these pessimistic days, professional esprit de corps will hardly .allow us to believe that no improvement in rates of mortality in any age-groups is possible. The answer of an actuary to any such criticism is that he is an arithmetician not a prophet, and the answer is
a
the "
improved. We hope
_
that the discussion initiated by this valuable paper will lead to further investigation of the whole subject.
THE CONTROL OF THE BLADDER WE have already referredto an investigation by Dr. D. DENNY-BROwN and Dr. E. GRABMB ROBERTSON into the control of micturition by the normal subject. Their important work has now been extended2 to patients with two types of lesion -destruction of the sacral roots of the spinal cord, and complete transection of the cord in or above the lumbar region, the cord being intact below the section. The effect of the first lesion is to destroy the central connexions of the pelvic nerves (nervi erigentes) which terminate peripherally in the vesical plexus, and of the pudic nerves which supply the external sphincter and other perineal muscles. The second lesion leaves these central connexions intact, but cuts off all communication with higher centres. The influence of the hypogastric nerves, originating in the lower thoracic and first lumbar segments and passing via the inferior mesenteric ganglion to the vesical plexus, is so slight that it may be neglected in this summary. 1 THE
LANCET, 1933, ii., 605. 2 Brain, 1933, lvi., 397.