Disease Transmission and Mans Resistance 295 



means producing) organism. The condition the microorganism 

 produces may be an infection. In some diseases products of 

 microbial metaboHsm, either in the presence or in the absence of 

 the cells which produced them, can initiate changes in the host 

 which cause symptoms of disease. Food poisoning exotoxins fall 

 into this category. Many microbes are non-pathogenic and do not 

 cause disease. 



Health and disease are relative terms. To a person who is 

 deathly ill, someone who "only has a sore throat or a common 

 cold" may be extremely healthy by comparison. But the cold 

 sufferer may feel that he is miserable when compared with some- 

 one else who, at the moment, exhibits no signs of illness. Disease 

 is rarely stationary. It may end in recovery, in permanent in- 

 jury, or in death. Health is defined by some as complete harmony 

 between the organism and its internal and external environment. 

 Virulence is the capacity of an organism to produce disease. Not 

 all disease is caused by microorganisms. There are a multitude of 

 malfunctions of an organic nature that have an etiology other than 

 microorganisms. 



Theories as to the cause of disease date to the beginning of 

 man's existence, and since the germ theory was not established 

 until about seventy-five years ago, how did man explain these 

 mysterious maladies which picked out an individual here, and cut 

 short the life of an individual there? Out of the multitude of 

 theories put forth through the ages, a few explanations had greater 

 support than other proposals that had been advanced and rejected. 



THE DEMONIC THEORY OF DISEASE 

 The concept that a body becomes possessed by evil spirits has 

 been one of the more popular explanations of that intangible 

 change that comes over persons who were in good health and 

 spirits such a short time previously. Some remote tribes still 

 employ witch doctors to drive out the demons or evil spirits with 

 incantations and ceremonies. Superstition has a powerful hold on 

 many "civilized" persons, as can be observed almost every day. 

 Bad luck ( evil spirits? ) will pursue that individual who chances to 



