MAN AND THE MICROBE 15 



fever, named from its supposed resemblance to typhus, and in olden 

 times a malady of comparatively less importance, remains one of our 

 grave sanitary problems. 



The only household pest which still generally persists in city and 

 country alike is the house-fly; and the public agitation against this in- 

 sect has grown to such proportions in recent years that we may now 

 look for substantial progress toward its elimination. The fly breeds 

 in horse manure and other deposits of decomposing matter and 

 it is always a carrier of filth, though only incidentally of disease. 

 In paved and sewered cities there is little evidence that the 

 fly is an important factor in disease transmission, but where 

 human excreta are exposed, as in rural districts or cities with badly 

 constructed privy vaults, the opportunity for flies to pick up the germs 

 of typhoid fever and other diseases and carry them to food is so great 

 that the danger becomes serious, particularly of course in the warm 

 climates of our Southern States. During the Spanish War 142 out of 

 every 1,000 of the men in our army camps contracted typhoid fever, 

 and 15 out of every 1,000 died of it; and it was shown that the incidence 

 of the disease was due mainly to careless disposal of excreta and conse- 

 quent facilities for fly transmission. In Jacksonville, Fla., Eichmond, 

 Va., and other southern cities remarkable results in the reduction of 

 typhoid and intestinal diseases have been attained by proper disposal 

 of excreta and anti-fly campaigns. It is by no means a simple matter 

 to control the multiplication of house-flies, but everything possible 

 should be done, by trapping and by the cleaning up of possible breeding 

 places, to reduce their numbers. 



The transmission of typhoid fever by insects is, of course, only 

 occasional and incidental, and even plague may at times assume a form 

 in which it is spread directly from man to man by the discharges from 

 the mouth. There is another class of diseases which are carried always 

 and necessarily by insects, the germ passing through certain stages of 

 its life history in man and others in the body of a particular insect 

 host. The most important example in temperate climates is malaria. 

 "Malaria," the bad air disease, was known to be somehow connected 

 with night exhalations from swampy land and a large amount of curi- 

 ously puzzling information about its prevalence was explained, only 

 when it was shown fifteen years ago that it is transmitted by the bite 

 of a particular mosquito which breeds in swampy pools and along the 

 weed-grown margin of streams. It then became clear that marshlands 

 did indeed cause malaria because their stagnant waters propagated the 

 mosquitoes which carried the malaria germ from man to man. Malaria 

 followed the turning up of the soil, not because emanations were set 

 free in the process, but because digging produces pools of water which 

 breed the insect hosts of the malarial microbe. The practical control 

 of mosquitoes and the consequent elimination of malaria has been 



