302 Microbes and You 



MECHANICAL AND PHYSIOLOGICAL BARRIERS OF MAN 



Unless we were endowed with powerful protective armor, the 

 hordes of microorganisms on us and around us would make our 

 life expectancy very brief indeed. Just as a military strategist 

 prepares for any eventuality to the best of his ability with the 

 weapons at his command, nature has provided us with two major 

 lines of defense against possible invading microorganisms. The 

 physical structure of our body is the first protective barrier. In- 

 ternal physiological forces step in when the first line of defense 

 has been breached. If the combination of these weapons is in- 

 sufficient to cope with the situation, and if medicine does not have 

 the proper last ditch stand weapons to destroy the pathogens, the 

 death of the animal is the expected consequence. 



EXTERNAL PROTECTIVE FACTORS 

 The Skin 



Contrary to popular belief, the human skin is not tissue paper 

 thin; it is composed of many layers of cells suitably interlocked to 

 prevent the entrance of microorganisms under normal conditions. 

 Because of the minute size of microbes, however, a large opening 

 is not required to invite penetration by bacteria. Since micrococci 

 found as normal skin inhabitants measure less than 1/25,000 of an 

 inch in diameter, it is easy to see that even though there are no 

 breaks in the skin visible to the unaided eye, bacteria can penetrate 

 what appears to be unbroken skin, and such infections as pimples 

 may result. 



Not only is skin a resistant physical barrier, it also contains 

 germicidal substances which are capable of destroying many 

 transient organisms which may lodge on the skin. 



The Stomach 



Considerable disagreement exists as to the germicidal action of 

 the stomach contents, but the physical barrier which the stomach 

 tissue affords is not questioned. The relatively high concentration 



