THE AUTOMOBILE AND PUBLIC HEALTH 289 



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 some- 

 where from ten to twelve days. Direct infection by mosquitoes as me- 

 chanical 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 auto- 

 mobiles 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 dim- 

 inished ; human lives will be saved and much added to health and com- 

 fort. 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. 



VOL,. LXXXIV. — -0. 



