PUBLIC HYGIENE AND SANITATION 413 



718. Mosquitoes. Mosquitoes are the carriers of malaria 

 and yellow fever. These diseases are due to germs which 

 must pass a part of their life in the body of a mosquito and 

 part in the body of a man, and their prevention depends 

 upon the extermination of mosquitoes. The extermination 

 may be effected by drying up all stagnant bodies of water 

 in which mosquitoes breed. Marshy land should be drained 

 dry, or its pools should be converted into running streams. 

 Barrels, pails, and cans of rain water and waste water 

 should be emptied. A little kerosene or other oil poured 

 on the water will kill the young mosquitoes. Persons sick 

 with malaria or with yellow fever should be protected with 

 screens of mosquito netting so that no mosquitoes may 

 become infected by them. By such means as these di- 

 rected against mosquitoes, tropical countries like Panama 

 have been almost freed from malaria and yellow fever. 



719. Pure food laws. Food that is exposed for sale in open 

 booths and in front of stores may become infected through dirt and 

 dust blown upon it, and from unclean persons handling it, and from flies 

 which alight upon it. Much food is adulterated, often with harmful 

 substances. Food that is kept too long may become spoiled and unfit 

 for use, and so antiseptics are often added to prevent decomposition. 

 Chickens that have been kept on ice for days and weeks without clean- 

 ing are poisonous and unfit for use. Until calves, lambs, and pigs are 

 at least a month old they are unfit to be killed for use as food. Milk 

 that is produced under unclean conditions, or that has not been kept 

 cool during its transportation, may become filled with bacteria and unfit 

 for use before it actually tastes sour. In these and other matters per- 

 taining to the purity or freshness of food offered for public sale, Boards 

 of Health are given great power of enforcing laws designed to prevent 

 abuses. 



SUMMARY 



I. Boards of Health have control over matters affecting 

 the public health- 



