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Dermatitis. The occurrence of skin affections in occupations is widespread ; they cause much pain and sickness but only rarely mortality. Investigation here has, therefore, perforce to be based pn other data than mortality statistics. The conditions associated with any form of dermatitis have to be inquired into until the specific cause is isolated. An instance will indicate the method used which is the same that led to discovery that silica alone among dusts possesses the specific property of predisposing to fibroid phthisis. Women employed in curing herring had long been known to suffer from erythema and painful indolent ulcers on their hands and on their arms, .which had been ascribed to many causes, such as the condition of fish. The salt brine, however, with which the herring are cured fell under suspicion ; then investigation in another industry in which brine is used for curing sausage-skins disclosed the presence among the workers of similar skin troubles; finally they were also found affecting men employed in brine mines. Clearly the salt brine was the cause. Workers handling potassium bichromate suffer in the same way, and those exposed to inhaling the dust of this compound suffer also from ulceration and perforation of the nasal septum. Next, workers inhaling fine salt dust were found with perforation of the nasal septum ; and other substances such as copper arsenite, water glass, arsenious acid, lime, and solutions of acid, were found to cause the same troubles. Search for a characteristic com- mon to all these compounds determined that all substances posses- sing hygroscopic properties could cause these forms of dermatitis, and that the pathological condition was due to the substance, after gaining access to the cutaneous tissue through some slight abrasion, abstracting fluid and so causing local necrosis. Acting on this theory, in some cases mere dilution of solutions used has abolished the trouble, while in other cases provision of opportunity for thor- ough soaking the skin after exposure has been equally efficient.

A further instance is also instructive. Certain workers employed in making roll tobacco were found suffering from dermatitis of the hands and forearms. These workers alone among tobacco operatives apply olive oil to the leaf. Other operatives much exposed to the oil were also found to suffer, and investigation estabjished that ex- posure to the oil was the causative influence. Similar dermatitis also occurs among washerwomen, among workers exposed to alkalis, among mechanics exposed to cooling and lubricating mixtures used in engineering shops, and workmen exposed to turpentine, petro- leum and other spirits. Here search for a common characteristic suggested that all substances with a lipoid affinity, i.e. capable of dissolving the natural fats, palmitin and stearin, from the skin could cause dermatitis by leaving the cuticle dry and liable to crack when infection from without can take place. Remedies by anointing the skin with lanolin and castor oil in order to replace the fat, and by adding antiseptics to the fluid used in order to guard against infection have proved their value and so support the theory.

Another group of skin affections which includes occupational warts is of considerable interest because of the light it throws upon the origin of epitheliomata. Workers who handle pitch, a distillation product of gas tar, and others who mix pitch with coal-dust in the manufacture of briquettes, suffer from warts which appear on the exposed parts of the skin, and also on the genitals. These warts show a special tendency to become epitheliomatous with the forma- tion of "pitch" cancer. Shale oil workers coming in contact with crude paraffin, a product obtained by distillation, similarly suffer from warts and " paraffin " cancer; but workers manipulating refined paraffin do not suffer. Chimney-sweeps have long been noted for their high death-rate from scrotal cancer which originates from exposure to soot, a distillation product of coal. Cancer of the lips and buccal cavity is nearly confined to males who by smoking expose these parts to the distillation product of tobacco. The evidence here summarized suggests that certain products obtained by distilling vegetable substances can sensitize the skin to cancer.

Evidence from the dye industry suggests that the products in question may possibly be benzene compounds. Workers in this industry exposed to certain amino-benzene compounds, particularly benzidine and naphthylamine (compounds which, when they gain access to the body, are excreted by the Kidneys), have been found to develop malignant tumours of the bladder. The new growths which occur on the skin in the tar cases, and in the bladder in the dye-work- ers, have certain features in common : at first there is a simple hyper- plasia ; the exact moment when malignancy supervenes is a matter of doubt; and metastasis is the exception. Possibly we have in these benzene compounds instances of substances which, by modifying tis- sue growth, possess the power of preparing the way for, if not directly causing, malignant changes. Much more research work on the lines here indicated waits to be done, for there are numerous other forms of industrial dermatitis, but the above instances should suffice to show how underlying principles of general utility come to light through investigations conducted in industry.

Miners' Nystagmus. This disease, chosen as an example of a trade neurosis, is one the incidence of which increases with length of employment. It takes on an average 20 years to develop; hence, it lays aside the miner when his skill is at its zenith and he is too old to change his occupation. The complaint is a distressing one which causes much morbidity, but no mortality, and in recent years has increased in prevalence.

The leading symptom is an uncontrollable wheel-like but irregular

rotation of the eyeball with the pupil as the hub of the wheel ; the sufferer sees the external world constantly moving and rocking before him. At the same time there are marked photophobia, rapid move- ments of the upper eyelid, and severe headache, which are accom- panied by symptoms of general neurasthenia. The condition fre- quently appears to lie " latent " and to develop suddenly after an injury (especially if to the eyes) or other depressing influence, such as an attack of influenza ; this tendency to be precipitated by trauma is even more pronounced than in the case of delirium tremens.

Formerly the disease was mistakenly ascribed to the posture of the coal-getter as he lay on his side holing the coal which necessitated unusual eye movements. Now, thanks to the work of Dr. T. L. Llewellyn, the condition is definitely known to be due to working in dim illumination. It occurs nearly exclusively among coal-getters and hardly at all among the men who convey the coal to the pit shaft or do other work on underground roads. It occurs with equal frequency among men standing at a 6-ft. seam, or kneeling at a 20- in. seam. The frequency of its occurrence varies with the amount of light provided ; the less the light, the more the disease ; it prevails especially in mines where oil safety lamps, which give a low illumi- nating power, are used, and is hardly known where naked lights are used, which give twice or three times the illumination.

The two factors which, acting together, sensitize the ocular nerve tracks to the disorganized movements characteristic of the disease, are poor illumination together with need for focussing vision; over 70 % of those affected are found to possess errors of refraction.

The condition improves if the worker gives up underground work, but tends to recur if he resumes it.

Two means of prevention are urgently needed: first, medical examination of all boys who desire to become miners in order to eliminate those with errors of refraction ; secondly, introduction of more powerful safety lamps. Electric safety lamps are now available, and where introduced, the prevalence has rapidly diminished.

Lead Poisoning. This disease affords an excellent instance of control guided by previous investigation and research, opportunities for which were provided by notification of the cases. Lead poisoning of industrial origin was made notifiable in 1895. Distribution of cases by industry and numbers employed then showed that exposure in manipulating metallic lead or moist lead salts was almost a negligible factor in causing the disease ; and that the governing risk was exposure to dust of lead salts soluble in the body fluids. Animal experiments proved that a dose of lead-dust when inhaled was a hundred times more toxic than when administered in food. Clearly preventive measures based, according to previous theories, on per- sonal cleanliness, but which neglected the danger from inhalation of dust and fumes, could not be expected to stop the disease. In Great Britain Dr. T. M. Legge of the Home Office, to whom credit is due for recognizing the particularly toxic nature of lead-dust when in- haled, concentrated attention upon preventing the generation of dust and fumes or upon removing them, if generated, from the atmosphere of work-places. This principle underlies a series of regulations applied to industries in which lead compounds are used, e.g. the manufacture of electric accumulators and of white lead, vitreous enameling, file-cutting, smelting of materials containing lead, the manufacture of paints and of pottery, tinning of hollow- ware, and heading of yarn. The result of action on these lines has been remarkable; 1,058 cases of lead poisoning were notified in Great Britain in 1900. Since 1900 industries have expanded so that many more persons are now exposed to risk; and in 1906 lead poisoning was made a compensation disease, a factor which tempo- rarily increased the notifications and tends to maintain them. Yet in 1918 the cases notified had fallen to 144 and in 1919 to 206.

Plumbism may be divided into two groups of cases: one, which occurs in the early weeks and months of employment, is characterized by such symptoms as acute colic and encephalopathy ; the second, which occurs after years of exposure, is characterized by nerve paralysis and chronic nephritis. The first group contains the vast majority of cases, and its disappearance in later years points to some degree to immunity having been acquired through continued ex- posure to subminimal toxic doses. Lead poisoning in this respect presents aspects of disease of which industry supplies other instances ; some exhibiting a prevalence which diminishes with length of expo- sure to risk, some one which increases with exposure to risk.

General Considerations. Mill fever, which affects most operatives on entering the cotton or flax industry, and certain forms of der- matitis, e.g. eczema and conjunctivitis due to contact with tetryl, and skin irritation from slag wool, provide examples of troubles which rapidly disappear with continued employment and do not reappear. On the other hand miners' nystagmus, Duyputren's contraction, pitch and paraffin cancer, bronchitis and pneumonia due to dust, cotton strippers' asthma, pulmonary silicosis, glass- blowers' cataract, phosphorus necrosis, and such trade neuroses as writers' cramp and telegraphists' cramp, are conditions which steadily increase in numbers with length of employment.

Other diseases resemble plumbism in presenting both early and late manifestations. Thus reference has already been made to the high incidence of accidents during early weeks and months of em- ployment; with advancing years as bodily activity declines, i.e. as the person becomes more sensitized to risk, the tendency to acci- dents again arises. Tri-nitro-toluene (T.N.T.) during the war caused