OCCUPATIONAL DISEASES 507 OCCUPATIONAL DISEASES measurement of the moon's parallax; and they are also occasionally employed in the calculation of longitudes. As the moon moves in her orbit from W. to E., the occultation of a star is made at the moon's E. limb, and the star emerges on the W. limb. When a star is oc- culted by the dark limb of the moon (a phenomenon which can only occur be- tween new moon and full moon) it ap- pears to an observer as if it were sud- denly extinguished, and this appearance is most deceptive when the moon is only a few days old. When an occultation occurs between full moon and new moon, the reappearance of the star at the outer edge of the dark limb produces an equally startling effect. OCCUPATIONAL, or INDUSTRIAL, DISEASES, diseases arising out of poisons, irritants, and similar causes due to specific conditions of labor. These maladies have been classified by W. G. Thompson in his "Occupational Diseases," into diseases due to irritant substances; those arising from defective surroundings, and special occupational diseases. The diversity of diseases due to what are known as dangerous trades has occupied attention since the great industrial development of the last cen- tury revolutionized conditions of labor, and it was soon ascertained that certain maladies regularly arose from certain occupations. Investigations carried on un- der diversified conditions in many indus- trial establishments have enabled medi- cal men to arrive on approximate conclu- sions regarding the probable specific character of the malady to be associated with a given occupation and environment. Irritant substances play the chief role in the propagation of diseases and these are divided by Mr. Thompson into six groups, namely, toxic metals and com- pounds; toxic gases and vapors; toxic fluids ; dusts and fibers ; germs ; and sub- stances of a general character. Anti- mony, arsenic, brass, lead, mercury are among the principal toxic metals and their compounds, which inhaled in the process of manufacture as vapor or dust or fume set up physical conditions favor- able to certain diseases. Toxic gases rank with the metals as prolific breeders of disease, and the list of the dangerous gases is a very long one. Aniline in coal tar; chlorine in the making of pot- tery; hydrogen chloride; sulphuric acid; carbon dioxide, called choke damp by miners; hydrofluoric acid; hydrogen sulphide, and zinc and arsenical fumes are some of the gases the absorption of which leads to symptoms of poisoning among workers exposed to their influence. Wood alcohol, which is largely used in many manufacturing processes, has been responsible for many deaths. Its fume;^ are extensively dangerous and blindness often occurs in cases where it is not fatal. The inhalation of ammonia and ammo- nium chloride results in cough and bronchitis. Benzine vapor if continually inhaled may result in a prolonged mal- ady. The use of white phosphorus in the making of matches was responsible for a great many fatal maladies, till laws prohibiting its use were passed in Europe. France for example has not had to record a single death from this cause since the year 1897 when the law was passed. Prohibitive taxes are producing a much similar result in the United States. The dangerous toxic fluids include pe- troleum, dyes, chinone, chinine, paraffin, tar, metal, and nitroglycerin. This last is a fluid of indeterminate color and it has been noted that those of good con- stitution who work in it usually acquire immunity. Its chief danger is in its ex- plosive capacity. In regard to dusts and fibers ordinai-y observation is witness to the obstruction of the respiratory organs, the irritation to eyes, ears, mouth, and mucous membranes which follows the absorption of particles comparatively harmless. _As a rule dusts consisting of large particles are liable to cause more lasting injury than the finer kinds of dust, and by their effect on the lungs are likely to set up conditions favorable to tuberculosis. Inquiry has made it clear that this disease among workers engaged in occupations that result in the inhala- tion of dust is more than twice as preva- lent as in other occupations. Workers in asphalt, cement, emery, glass, stones, in mining, and the grinding, cutting, crush- ing, and polishing of metals, marbles, and stones are among those most liable to suffer from the inhalation of particles. Maladies arising from germs are preva- lent in the tanning and wool-sorting trades, and in occupations that keep workers continuously among cattle and horses. To these classes may be added irritants of a general character, outside those here enumerated. Dangerous surroundings, as Mr. Thompson shows, are responsible for a large number of maladies, and among these harmful conditions of the air lead to obvious symptoms. Workers in min- ing, tunnels, and caissons are subject to a number of maladies peculiar to their work in compressed or bad air. Occupa- tions which require continued strain, long abstinence from food, and similar abnormalities naturally lead to results which affect the nervous systems as well
