CHAPTER 16 



Disease Transmission and 

 Man^s Resistance 



DEFINITION AND THEORIES OF DISEASE 



MODES OF TRANSMISSION AND PORTALS OF ENTRY 



TYPES OF DISEASE 



MECHANICAL AND PHYSIOLOGICAL BARRIERS OF MAN 



FACTORS AFFECTING RESISTANCE TO DISEASE 



IMMUNITY 



ANTIGENS AND ANTIBODIES 



PREVENTIVE MEASURES IN DISEASE 



DEFINITION AND THEORIES OF DISEASE 



It is difficult to define disease. Vl^hen freely translated the word 

 disease means a lack of being at ease— a state of discomfort. 

 Discomfort is not always caused by disease, but disease always 

 results in some malfunction or discomfort, whether it be to a cell, 

 to a tissue, or to an entire body. Disease may be considered as a 

 departure from normal (whatever noimal is), or perhaps a harm- 

 ful departure from what might be considered the well-being of an 

 individual. When a microorganism is the cause of this discomfort, 

 we designate it as a pathogenic (pathos means sadness, and genie 

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