CHAPTER IV* 



CONTROL OF INFECTIOUS DISEASES 



Principles 



That the infectious diseases can be controlled depends upon the 

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

 agent; that they pass from patient to prospective patient only because 

 the infective agent passes from patient to prospective patient; and 

 that therefore the prevention of effective passage will prevent the 

 spread of the disease. These preventive measures with their natural 

 incidental developments constitute the practice of present public health 

 relating to these diseases. 



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, whooping cough, smallpox, chicken- 

 pox, pneumonic plague, leprosy) are received almost exclusively 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 abra- 

 sion. But these are rare methods of transmission as compared with the 

 mucous to mucous forms, except in syphihs and chancroid where they 

 frequently occur. 



The routes of travel between the patient and the prospective pa- 

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



* Prepared by H. W. Hill. ' 



850 



