ELIMINATION OF GERMS FROM PATIENTS 219 



It has been proved recently that yellow fever also is dis- 

 tributed by mosquitoes rather than by direct personal con- 

 tagion. The species of mosquito is different from either of 

 those shown in Fig. 70, and lives only in warm climates. 

 Mosquito netting is the best check for this disease. Yellow 

 fever has been almost wholly stamped out of Havana by 

 simply surrounding the patients with netting, thus pre- 

 venting' the mosquitoes from biting them an.d becoming 

 infected with the germs which they might carry to other 

 persons. It has also been banished from the Panama 

 Canal zone by draining the swamps and closing up the 

 breeding places of mosquitoes ; and the last time that yellow 

 fever invaded the United States it was speedily crushed out as 

 soon as active measures were taken to destroy mosquitoes 

 and prevent their breeding. 



In all tiTily contagious diseases the parasites have some 

 means of leaving the body of the patient. Their methods 

 of exit are numerous, but are not very diffi- 

 cult to determine in the case of any particular f\ (■■■.'*' ^ 

 disease. Most types of contagious diseases | *J-*<.^,'- 

 have suggestive symptoms. For example, in . sSX/ 

 smallpox, scarlet fever, or measles there is an ''**^ 



eruption of the skin, and it becomes probable of /;' htheria"^ 

 at once that this eruption is a means of elimi- 

 nation of microorganisms. In diphtheria (Fig. 71) the germs 

 grow in the mouth, clinging to the surfaces inside the mouth 

 and throat, and it is quite evident that the breath, or at all 

 events the forcible breath that comes with coughing, will 

 detach the bacteria from their position in the throat and 

 blow them into the air. In the case of whooping cough 

 the violent paroxysms of coughing are probably a means of 



