himself, by avoiding dealers whose premises harbor filth and the flies it breeds 

 or attracts. And we can all help by keeping our own premises clean and free 

 from flies. 



Mosquitoes and Malaria Of all the diseases from which man has suf- 

 fered, malaria is said to be the most widespread. It occurs all around the earth 

 and as far north and as far south of the equator as mosquitoes breed. Wher- 

 ever malaria is present, it shortens life, it keeps people from their work, it 

 reduces human capacity to work and to enjoy Hfe, it demands costly drugs, 

 nursing, and medical services, and it throws millions of fertile acres out of use. 



In India malaria kills over a million human beings a year, besides causing 

 untold misery to millions of others. A French scientist, Alphonse Laveran 

 (1845-1922), working in Algeria, was able to infect volunteers with the blood 

 of malaria patients, but he could not find out how infection takes place 

 naturally. The disease is caused by any one of three or four species of protozoa 

 related to the ameba and known as the plasmodium of malaria. The animal 

 feeds upon the red corpuscles of the blood of its host and then spondates, that 

 is, breaks up into a large number of tiny bits of protoplasm called spores. The 

 spores enter new^ corpuscles, and the process is repeated indefinitely, greatly 

 weakening the victim and sometimes killing him (see illustration, p. 622), 



In 1900 scientists in England and Italy co-operated in an elaborate experi- 

 ment to find the connection between malaria and mosquitoes. A number of 

 volunteers lived in the badly malarious Roman Campagna through the most 

 dangerous part of the year, from early in July until late in October. But they 

 lived in houses that were carefully screened against mosquitoes, and when they 

 went out in the evening (when Anopheles is about), they always w^ore veils 

 and gloves. Not one became sicJ{, although many of their neighbors became in- 

 jected with malaria during the summer. 



At the same time, some mosquitoes were caught and allowed to suck blood 

 from malaria patients. These mosquitoes were shipped to England in little 

 cages, and stung two young men who had never suffered from the disease and 

 who lived in a region where there had been no cases of malaria. In the course 

 of a few days both developed the characteristic symptoms of the disease. 



This experiment showed that (1) the night air and the vapors from the 

 swamps of the Campagna are harmless and (2) the sting of a mosquito that had 

 once bitten a malaria patient is dangerous. Mosquitoes raised from the eggs 

 and allowed to bite a person do not transmit the disease. Nor does drinking 

 water in which the mosquitoes develop. Today nobody who knows the facts 

 can have any doubt as to the relation between the mosquito and the trans- 

 mission of malaria (see illustration, p. 623). 



Mosquitoes and Yellow Fever In the past yellow fever has been much 

 more fatal than malaria. It occurs only in tropical or semitropical regions, 

 although there have been epidemics of yellow fever as far north as Philadel- 



621 



