ELIMINATION OF GERMS FROM PATIENTS 219 



of covering doors and windows of houses with mosquito 

 netting has produced a marked decrease in the amount 

 of malaria in these dwellings. 



It has been proved recently that yellow fever also is 

 distributed by mosquitoes rather than by direct personal 

 contagion. 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 preventing the mosquitoes from biting them 

 and becoming infected with the germs which they might 

 carry to other persons. 



In all truly contagious diseases the parasites have some 

 means of leaving the body of the patient. Their methods 

 of exit are numerous, but it is not very 

 diflficult to determine, in the case of any i\ f <:^ 

 particular disease, the methods by which I *J^^A 

 the parasites leave the body. Most types . AV/ 

 of contagious diseases have suggestive ""***' 



symptoms. For example, in smallpox, scar- F'^- 7i- Bacillus 



. .of diphtheria. 



let fever, or measles, there is an eruption 

 of the skin, and it becomes probable at once that this 

 eruption is a means of elimination 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 



