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rest pauses had not already been scientifically introduced in order to prevent fatigue; but this result cannot be expected to follow where the machine sets the pace and the human element is at a minimum, (ix.) Good lighting, whether artificial or natural (but artificial cannot be as good as natural and is always expensive) improves health and output. Window-cleaning and attention to gas mantles and electric light bulbs are economic propositions, (x.) Change of occupation, apart from all these matters concern- ing environmental conditions and hours of labour, has a serious effect upon health; during the first weeks and months at new work while for lack of experience output is low in quantity and quality, the incidence of industrial accidents and sickness is unusually high, (xi.) Research has revealed that workers tend to drift from one place of employment to another to an extraordinary extent, and that a labour turnover of 100% per year is rather below the average. This drift, which has been estimated to cost industry 80,000,000 a year, can be largely reduced by personal super- vision of workers, (xii.) Working clothes suited to each process are important, in order to permit adaptability of the body temperature and avoid perspiration, (xiii.) A clean skin is of special value to workers to enable them to react to ventilation and avoid septic wounds.

Much more remains to be found out from industry about human efficiency and human health. Already sufficient has been done to demonstrate the existence of a new science aimed primarily at preserving health, and incidentally at greatly increasing industrial capacity. The keystone to the position is that the influence of occupation upon a community cannot be appreciated unless from the first its value for establishing and maintaining health is accepted. Work represents the katabolic side of metabolism and is as necessary to life as is rest, the anabolic side. The study of human activity and its maintenance is the study of health. An important Anglo-American publica- tion, The Journal of Industrial Hygiene, is devoted to the subject.

Medical Service. Knowledge is useless unless it receives practical application, and the employment of doctors by industrial establish- ments is the means to this end. The work to be done varies with the number of employees.but a personnel of 2,500 at an engineering factory provide ample work for a whole-time medical officer if he is entrusted with such duties as examining each applicant for work ; caring for the health of those employed by periodical re-examination as required; supervising ambulance and first-aid work ; visiting absentees whether injured or sick ; controlling the hygienic conditions of workshops, canteens, sanitary conveniences, lavatories and washing accommo- dation; advising as to faulty posture at work, accident prevention, suitable working clothes, and as to how to fit the worker to the work ; keeping personal records of health; and, most important of all, conducting investigations into these records. For smaller establish- ments a plan has been promoted by a number combining to employ a medical man, remunerating him on a capitation basis of those em- ployed. The expense involved in a factory medical service has always been found to be a good investment, since the loss incurred from labour turnover, from lost time, from accident compensation, and from many other causes, is diminished to an extent which is far in excess of the outlay.

Industrial Diseases. Description of every form of disease which may be influenced by occupation would be description of every ill to which the flesh is heir. A r6sum6, nevertheless, may indicate how study of the incidence of morbidity and mortality in different occu- pations throws light on some of the difficult problems connected with the aetiology of disease. The multifarious forms of occupation, particularly those of manual workers, provide opportunities for studying the effect of different influences upon the human organism. Even if data did not exist to prove the point, reason would lead one to expect great variety in the morbidity and mortality experienced by agricultural labourers, coal-miners, textile operatives, boot- makers, chemical workers, shop-keepers, boiler-makers, stone- masons, fishermen, clerks, furnacemen, engineers and many others. Careful inspection of existing data reveals not only that marked differences do exist, but that they are differences in kind as well as differences in bulk that is to say a high occupational mortality may be, and indeed usually is, due to an excessive death-rate from one or a few causes, rather than to a high death-rate from all causes. Thus chimney-sweeps suffer excessively from cancer, stone-masons from diseases of the lungs, coal-miners from accidents, and printers from phthisis, without necessarily experiencing any increased mor- tality from all other disease. Further inspection discloses not only an increased incidence of diseases such as are experienced by the general community, but also the occurrence of certain diseases peculiar to certain industries, what are known as diseases of occu- pation, for example, poisoning from lead, mercury or phosphorus,

tubercular silicosis and miners' nystagmus. This latter group has, like all other things which are strange and unusual, drawn more at- tention than has the influence of occupation in increasing the prev- alence of more common forms of disease. Nevertheless the in- fluence of occupation upon the common forms of disease is far more important. Instances are chosen in what follows to illustrate the importance of industrial medicine. Each disease mentioned here- after is only referred to as an illustration of how obscure problems may be illuminated and how principles underlying the causation and prevention of disease may be disclosed by study of occupational morbidity and mortality.

Accidents. Objection may possibly be raised to including acci- dents among diseases, but careful inquiry into the incidence of industrial accidents has revealed that we succumb to accidents much as we succumb to those forms of ill-health commonly attributed to infection. In other words the incidence of accidents obeys epide- miological laws. Accidents are found to occur with greater frequency with advancing years, just as does cancer. The risk of accidents is greater in some industries, such as mining, than in others; just as tuberculosis is more prevalent in slums. Accidents due to different causes, say falls of roof in coal-mines, cause similar death-rates from year to year, and a similar proportion of total accidents^ just as pneumonia year by year causes similar death-rates, and forms a similar proportion of total deaths. Accidents to different parts of the body, say to the eye, form year by year the same proportion of accidents to all parts; just as tuberculosis of the peritoneum forms the same proportion of tuberculosis of all regions. Accident- occurrence is affected by hygienic conditions fatigue, psychical influences, ventilation, lighting, and temperature in the same way as are general illness'and disease. Accidents in any community are distributed not according to pure chance, but according to varying individual susceptibility; just as certain diseases run in families, due to " inherited predisposition." Workers nevyly exposed to risk sustain a high proportion of accidents, which'diminishes with length of employment; just as lead poisoning claims most of its victims among new workers, or as South African natives succumb to pneu- monia when first introduced to civilized communities.

Study of industrial accidents on the above lines indicates that the origin of the vast majority lies in the physiological and psychological state of the worker and his reaction to his environment ; that the origin of other forms of morbidity and mortality is in the long run similar, and that the most promising way of attacking the incidence of accidents and of disease is through interesting the community individually in the need for maintaining personal health and resisting power, rather than by encouraging implicit reliance upon protective guards, whether they take the form of fencing machinery to prevent accidents, or using so-called disinfectants to prevent infection.

Action directed to this end is known as the Safety First movement with which the general community is acquainted. In the industrial world steps are being taken to interest the workers by forming in factories accident committees representative of all classes employed. Each accident as it occurs is investigated and reported upon by the committee, and in this way the members, who only serve for short periods of about six months, become acquainted with the principles of accident prevention. The prevalence of accidents where such committees exist has been reduced to an extent as satisfactory as it is surprising. The lesson to be learnt from a study of industrial accidents is that the general health of the community depends upon each individual understanding that his own health is largely in his own hands and that he owes to himself and to the community the duty of maintaining it.

Phthisis. The occurrence of disease in general may be held to depend on a chain of three links. The first represents a latent capac- ity to be affected what is known as hereditary predisposition which is present in varying degrees in different individuals ; so long as this capacity is latent exposure to risk has no effect. The second represents activation of this capacity or sensitization of the individ- ual ; exposure to risk now is followed by disease. The third represents risk; which in the case of phthisis is exposure to infection by the tubercle bacillus. Occupations tend to select individuals according to their latent capacity, inasmuch as industries calling for strenuous exertion, such as mining, metal-smelting, and agriculture, call for those physically fit, while indoor and sedentary occupations, such as tailoring and printing, tend to be followed by more weakly individ- uals. There is, however, no evidence that these weakly individuals are especially weakly so far as phthisis is concerned, and they might be expected to suffer in equal excess from all causes of death. But the incidence of phthisis suggests that certain occupations sensitize workers to the normal risk from infection, while others increase the risk; and study of the occurrence of phthisis in industry is found to support the general view of disease here stated, although difficulty may occur in any particular industry in determining whether the second or third link is the more important..

Study of the distribution of phthisis according to sex and occupa- tion is of great interest in this connexion. Distribution according to sex is important because males as a class are employed away from their houses so much more than females that they may be held to represent the influence of occupation. Distribution according to occupation indicates what influences are favourable, what unfavour- able. Phthisis is an index disease, that is to say its incidence rises