288 HEALTH AND DISEASE 



symptoms of disease. The transmission of an infectious 

 disease from one person to another is brought about by 

 the transference of microbes either directly by contact 

 from person to person; or indirectly, through common 

 contact with intermediate objects, as door knobs and 

 furniture, or through inoculation by the bites of in- 

 fected insects. For example, a person with diphtheria 

 may transmit the microbes directly by coughing into 

 another person's face or by touching some part of his 

 skin; or he may transmit them indirectly by leaving 



Anopheles (malaria) 



.Anopheles (malaria) Culex (common) Stegomyia (yellow fever) 



FIG. 152. Various types of mosquitoes. (After Howard and Underwood.) 



some of them upon a door knob or chair back which the 

 other person subsequently handles. Had the disease 

 been malaria or yellow fever, the person might have 

 transmitted the microbes indirectly through the bite of 

 a mosquito. The microbes thus transmitted are in a 

 position to enter the body of the well person, provided 

 that they can find a cut in his skin or are conveyed 

 to his mouth. In the case of the insect's bite, they are 

 actually injected under the skin. 



Entrances and exits for microbes. The main en- 

 trances by which infecting microbes enter the body of a 



