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Rh toxic jaundice among munition workers, but hardly any cases occurred among those who had been employed over six months; it also caused aplastic anaemia, a condition which was rarer and only appeared among those who had been employed for a considerable period. Phthisis also presents some similarities, for there is evidence that exposure to a subminimal dose may result in increased resistance; possibly the tendency for the curves representing the phthisis mortality of boot-makers and general labourers to fall towards that of the standard after middle life indicates some degree of acquired immunity; on the other hand tuberculosis among those sensitized by inhaling silica-dust shows no signs of falling off in later years, and may be held to be analogous to the late group of plumbism cases, the aplastic anaemia cases, and accidents in late life.

There are, however, trade diseases which appear to have no relation to the period of employment. The incidence of these depends directly on exposure to risk; among these diseases are anthrax, caisson disease, and gassing from carbon monoxide, nitrous fumes, and arseniuretted, sulphuretted or phosphoretted hydrogen. These diseases, however, are rare, and their causation and prevention is comparatively well understood.

The lesson which emerges is that although the human body often possesses a capacity which requires no sensitization to succumb when exposed to certain unusual risks, it also possesses a capacity for defending itself against risk if the exposure is long continued. On the other hand certain influences such as alcohol, over-fatigue, lead, dietetic insufficiency, or silica-dust, can gradually sensitize the body, even to the extent of breaking down an acquired immunity, so that it finally succumbs where it formerly resisted. The methods by which immunity is acquired (as against such a thing as tetryl) and by which it is lost through sensitization (as by inhaling silica) both probably await biochemical research to explain their meaning. The problems associated with occurrence of trade neuroses, on the other hand, call primarily for physiological investigation into the normal mechanism of coordinated and balanced nervous control.

Industrial medicine, in which the absence of a disease in any group of workers may go far to explain its causation in another allied group, provides unique opportunities for studying the normal physiological elasticity of health and the way in which it may be overstrained and give place to disease.

—J. Goldmark, Fatigue and Efficiency (1912); Industrial Efficiency and Fatigue, Health of Munition Workers Committee, Interim Report 1917 (Cd. 8511); Industrial Health and Efficiency, Health of Munition Workers Committee, Final Report 1918 (Cd. 9065); H. E. Mock, Industrial Medicine and Surgery (1919); E. L. Collis and M. Greenwood, The Health of the Industrial Worker (1921); Industrial Fatigue Research Board, various reports during and since 1919; J. T. Arlidge, Diseases and Mortality of Occupations (1892); T. Oliver, Diseases of Occupation (1908); G. M. Kober and W. C. Hanson, Diseases of Occupation and Vocational Hygiene (1918); R. P. White, Occupational Affections of the Skin (1920); T. M. Legge and K. Goadby, Lead Poisoning (1912); E. L. Collis, Industrial Pneumonoconioses (1919).

 INDUSTRIAL WORKERS OF THE WORLD, THE.—A union of wage-earners in the United States, organized in 1905, with a membership in 1920 of about 100,000, commonly spoken of as the I.W.W. (For a discussion of the I.W.W. see .)  INFANTILE MORTALITY.—Since 1910, the social importance of measures for reducing the rate of infantile mortality, which means the number of deaths under one year of age per thousand births, still-births being excluded from both figures, has come into increased prominence. The problem involved, however, presented special difficulty early in 1921 to anyone who sought to deal with it authoritatively, since the World War had upset all calculations and statistics. In some cases, as in all the central European countries, the infantile death-rate had increased to a really appalling extent. One competent observer, for example, during a prolonged stay in Vienna, did not notice one “toddler” in the streets. On the other hand, there was, according to the British Registrar-General’s reports for 1919, an apparent fall in infantile death-rate. No contemporary figures were yet available from the central European countries. Moreover, during the war, so great had been the pressure of work in all the countries involved that the statistical returns required, from which to draw conclusions of any lasting value, were perforce allowed to lapse.

A great deal of interesting information is to be found in Professor Starling’s Report on Food Conditions in Germany with Memoranda on Agricultural Conditions and Statistics, published in 1919 (Cd. 280). The great outstanding difference between Great Britain and Germany in this respect was that of distribution. In England the control of distribution was facilitated by the fact that 80% of the grain and 45% of meat and all the oil-seeds consumed in the country were imported, and therefore could be controlled by the administration from the moment of their arrival. In Germany the whole of the supplies were produced in the country and had to be obtained from the large and small farmers. Thus a highly complicated and very difficult method of collection and distribution had to be followed, and grievous mistakes were made. Much more hoarding took place in Germany than in England, and the producers were far better fed than were the non-producers. The food shortage therefore was mainly experienced by the inhabitants of large towns and industrial areas. These observations are borne out by such books as An English Wife’s Life in Berlin during the War by Princess Blücher. Moreover the German authorities felt themselves obliged to attempt to ration strictly the whole food of the population, and no such system as this can succeed without mass feeding. No two individuals are alike; one will need more food than the other. In England rationing was wisely confined to certain articles, such as meat, fats and sugar,—leaving bread, the chief food of the poor, unrationed, so that each individual could obtain of this as much as he required.

In Germany, in common with the other belligerent countries, as a result of the absence of the adult male population, the birth-rate went down. In addition to this cause the diminished fertility of the population owing to chronic underfeeding of both sexes must be taken into account. The birth-rate in Germany dropped from 27·5 per 1,000 in 1913 to 15·83 in 1916, and 14·29 in 1917, so that the number of births at the last date was well below the number of deaths, and in 1918 the deaths per 1,000 were 16·30 as compared with births 9·45, or a surplus of deaths per 1,000 of 7·35. In spite of the condition of malnutrition of the mothers, the children were normal when born, a state of things borne out by observations everywhere. Their further development was of course hampered by the lack of nourishment of their mothers, as well as by the defective supply of cows’ milk. The pre-war milk consumed by Berlin was 1,250,000 litres, which during the war diminished to 225,000 litres, an amount totally inadequate to the necessities of the babies. How large a share the question of distribution had in the increase of infantile mortality in Germany was shown by the statement issued by the Belgian Relief Commission. Owing to the uniform feeding there was very little evidence of serious malnutrition among the inhabitants of Belgium, and the mortality among the children during the years of German occupation was less than before the war. It is highly gratifying to know that infantile mortality was steadily dropping throughout the world during 1900–20. It is true that the birth-rate was also dropping. The time was not yet ripe in 1921 to attempt to estimate the total loss of births caused by the war.

The births registered in the United Kingdom during the years 1910–4 were 4,411,823 as against 3,623,579 during an equal period of time 1915–9, a difference of 788,244. But the numbers born were already decreasing before the war notwithstanding the increase of population, so the whole diminution should not fairly be attributed to this cause. Also there has been a great recent rebound of fertility, not yet at an end in 1921, which may be regarded as a partial offset. The British birth-rate during 1919 went up in all districts except Wales, where, contrary to the usual experience, it went down. The increased rate was specially marked in London.

The British death-rate among male infants is always steadily higher than is that among female ones, and this rate has apparently been rising, though there was a curious drop in 1918. Taking the years 1911–19, 120 male to 100 female babies died, and this rate steadily increased till 1919 when it reached 124, having dropped in 1918 however to 114. The infant deaths registered for the year 1919, according to the latest figures available, were 12·2% of all deaths at all ages. The total number who died were 61,715. This proportion has fallen very rapidly of late years, not only because of fewer deaths, but also of fewer births. The percentage of infantile deaths of the total number as recently as 1901–10 was 22·6.

The rate of infantile mortality resulting from these deaths during 1919 was 89 per 1,000 births, or 15·2% below the average of the previous 10 years. It was the lowest rate that had yet occurred in the United Kingdom, the nearest to it being 95 in 1912. 