Page:Popular Science Monthly Volume 84.djvu/289

Rh One of the missions of autotrucks will be the transferring of loading and unloading of freight beyond the city limits. The carrying of freight to warehouses on autotrucks will necessitate complete renovation of roads and construction of relatively dustless road beds. Incidentally this will also do away with much irritating smoke from locomotives. It has been stated that transportation of freight by autotrucks within city limits is economical both in time and expenditure. Improvement in city streets has followed in the wake of the introduction of electric street cars and the decreased use of horses in cities due to automobile traffic will increase possibilities in this direction.

The injurious influence of dust on the public health is of various nature. The mechanical irritation of the respiratory tract and the accumulation of dust in the lungs and eyes increase susceptibility to infections. Inflammations of the conjunctiva, due to infection with such common, usually considered innocent, germs as the ubiquitous hay bacillus, have occurred. Probably such infections follow mechanical irritation of the mucous membranes by dust or other causes. The hay bacillus is carried everywhere by dust. It must be remembered that dust is the carrier of germs—harmless as well as injurious ones. Bacteria, yeasts and molds rarely travel alone. They are generally kept in suspension by floating particles of dust. It is due to this fact that after snow and rain storms there are relatively few microorganisms in the air. Therefore any provision, which materially reduces the amount of dust will reduce the number of microorganisms in the air. Among such provisions improvement of road pavements takes a prominent place, since dust in the air can come only from the ground by the action of winds or moving vehicles.

The diseases which may be communicated by dust are manifold. The germs of pneumonia, various forms of tonsillitis, diphtheria, croup, whooping cough, colds and tuberculosis are undoubtedly carried by dust. In fact, probably all infections of the respiratory tract may be carried in this fashion. Germs of the diseases named have been isolated from the air. The germs of tuberculosis are carried chiefly by the sputum of affected persons and communicated either by inhalation of dust or by food on which germ-laden dust is deposited. It must not be understood that this is necessarily street dust, but no doubt street dust is a contributory factor.

Diseases of the intestinal tract may also be communicated by dust. Food and water, if contaminated with sewage, are the commonest vehicles of infection in typhoid fever and dysentery, but it is quite conceivable that some cases of obscure origin may be the result of dust inhalation or ingestion of raw food on which dust has fallen. Studies of typhoid fever epidemics have led sanitarians to recognize that food and water do not account for all cases and sometimes disease may be due to