Page:Popular Science Monthly Volume 84.djvu/293

Rh The germs of these diseases undergo a well defined cycle of development in the body of the mosquito. For mosquitoes to become a menace it is necessary for them to bite a human subject suffering from malaria or yellow fever after which a period of incubation has to elapse before the bite of the insect becomes dangerous. This incubation period lasts somewhere from ten to twelve days. Direct infection by mosquitoes as mechanical carriers of germs is relatively scarce. Besides, mosquitoes are not universally susceptible to the diseases mentioned. Only certain species can act as intermediate hosts. Since flies are mechanical carriers the possibilities of infection by these insects is greater than by mosquitoes.

The probable benefits that will result from the increased use of automobiles and autotrucks may be summed up as follows: (1) With the universal construction of smooth and non-absorbent roads and the use of oil instead of water for sprinkling, the quantity of dust in the air will be reduced. As a consequence a number of diseases which are frequently transmitted by dust will be decreased and storm waters will be more easily cared for. (2) The horse will gradually disappear from our streets. With it the number of house flies and stable flies will be diminished; human lives will be saved and much added to health and comfort. Contact infections of those engaged in the care of horses will also become rare. At the same time out of door life and enjoyment will be encouraged and thus a further contribution to the betterment of human conditions brought about.