CHAPTER IV.* 

 CONTROL OF INFECTIOUS DISEASES. 



PRINCIPLES. 



That the infectious diseases can be controlled depends upon the fact 

 that they arise only in the presence of a specific living infective agent; 

 that they pass from patient to prospective patient only because the in- 

 fective agent passes from patient to prospective patient; and therefore 

 that the prevention of effective passage will prevent the spread of the 

 disease; these preventive measures with their natural incidental develop- 

 ments constitute the practice of present public health. 



In general the infective agent leaves the body of the patient by the 

 mucus-lined orifices of the body, the nose and the mouth, the anus, 

 the urethra, the mammae, and the genital organs. In general it must, if 

 it is to infect successfully another person, reach one or more of the same 

 mucus-lined orifices of that other person. Excluding the venereal 

 diseases the ordinary infectious diseases (tuberculosis, typhoid fever, 

 diphtheria, scarlet fever, measles, whoop.'ng cough, smallpox, typhus 

 fever, plague, leprosy) are almost exclusively received into the body 

 through the mouth (or nose) . While the passage is usually from mucous 

 membrane to mucous membrane as above outlined, the infective agent 

 may pass effectively from mucous membrane to cut or abrased skin 

 (the uninjured skin is probably almost always resistant to these infections) . 

 Again, in those diseases where skin lesions are a prominent feature 

 (smallpox, plague, leprosy) the infective agent may -pass from the skin 

 lesions to a mucous membrane, or to a cut or abrasion. But these are 

 rare methods of transmission as compared with the mucous to mucous 

 form, except in syphilis and chancroid where they frequently occur. 



The routes of travel between the patient and the prospective patient 

 are many. At times, mucous membrane may be applied to .mucous mem- 

 brane as when a well person kisses a diphtheritic child; conveyance of 

 particles through the air, sprayed from the mouth, may occur, as when a 



* Prepared by H. W. Hill. 



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