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THE IMPROVEMENT OF MORTALITY-RATES

THE LANCET

LONDON: SATURDAY, MARCH 31, 1934

ELSEWHERE in thjs issue we print a paper byDr. KERMACK, Colonel McKENDBiCE, and Dr.McKlNLAY which will interest a circle of readers

beyond the students of mathematical and statis-tical problems to whom the three authors are

already well known. It shows that if the rates of

mortality of England and Wales in decennial age-groups are expressed as a percentage of the ratesobtaining at a particular previous epoch and

arranged on a chess-board in which rows corre-

spond to secular time and columns to life time (seep. 699, Table II.) the result is that the entries inthe diagonals are approximately equal. Forinstance, when expressed as a percentage of therate prevailing in 1841-50, the rate of mortalityin the age-group 5-15 in 1861-70 was 87, the rateof mortality in the age-group 15-25 in 1871-80was 75, the rate of mortality in the age-group25-35 in 1881-90 was 74, the rate of mortality inthe age-group 35-45 in 1891-1900 was 81, and,proceeding thus, we have 84, 84, and 82, the lastfigure being the rate of mortality in the age-group65-75 prevailing in the decennium 1921-30,expressed as a percentage of the correspondingrate in 1841-50. A similar rule is found to holdfor Scottish experience. The longer secular recordof 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 intri-

cacies of statistical problems to be dogmatic intheir interpretation of these results, but their

paper should stimulate research in many direc-tions. Probably some of our unmathematicalreaders who, declining to be terrified by a repulsivesymbolism and such vaguely terrifying phrases as"

complete expectation of life," " curtate expecta-tion of life," and so on, have discovered what thoseportentous documents the National Life Tablesreally mean, have recalled a line in Horace con-cerning the obstetrics of mountains. For the lastEnglish Life Table does not tell us how the genera-tion in being in 1921-23 will die out, but how itwould die out if the rates of mortality prevailingin every age-group in those three years were neverto change. And even in these pessimistic days,professional esprit de corps will hardly .allow usto believe that no improvement in rates of mor-tality in any age-groups is possible. The answerof an actuary to any such criticism is that he isan arithmetician not a prophet, and the answer is

unexceptionable ; but the retort is also unexcep-tionable-namely, that his table does not tell uswhat most people are interested to know-whatis likely to happen to them. Out of official hours,some actuaries (especially, we think, some Italianwriters) have toyed with the idea of current lifetables-i.e., of constructing tables in which therates of mortality at advancing ages are basedon advancing secular experience. KERMAOK,McKErrDRacA, and McKiNLAY point out a hopefulway of trying to do what we all wish to have done.In view of their results, it does not seem quite sochimerical as it once did to suppose that we mightconstruct a life table which would tell us whatthe " expectation of life " of men now aged, say,40 really is. Naturally, as they point out, muchmore detailed analysis will be required before any-thing could come of the proposal, but they havesuggested a method, and in language all intelligentreaders can understand.How far their explanation-namely, that environ-

mental factors up to the age of 15 are of over-riding importance-is acceptable cannot be deter-mined. Of course some will point to the historicalfact that in industrial life the legislature inter-vened to safeguard the children before any pro-tection was given to adults. It is, however, verydifficult to propound a plausible working hypo-thesis of delayed environmental reforms, passingfrom age-group to age-group, which will adequatelyaccount for the results. It is hardly necessary toadd that the authors do not suggest that environ-

< mental factors cannot influence rates of mortalityat later ages ; their data are derived from countriesand epochs in which (if we exclude war periods)on the whole the conditions of life at all ages haveimproved. _

We hope that the discussion initiated by thisvaluable paper will lead to further investigationof the whole subject.

THE CONTROL OF THE BLADDERWE have already referred to an investigation

by Dr. D. DENNY-BROwN and Dr. E. GRABMBROBERTSON into the control of micturition by thenormal subject. Their important work has nowbeen extended 2 to patients with two types of lesion-destruction of the sacral roots of the spinal cord,and complete transection of the cord in or abovethe lumbar region, the cord being intact belowthe section. The effect of the first lesion is to

destroy the central connexions of the pelvic nerves(nervi erigentes) which terminate peripherally inthe vesical plexus, and of the pudic nerves whichsupply the external sphincter and other perinealmuscles. The second lesion leaves these centralconnexions intact, but cuts off all communicationwith higher centres. The influence of the hypo-gastric nerves, originating in the lower thoracicand first lumbar segments and passing via theinferior 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.