498 DEFENSES AGAINST DISEASE 



to the germs which it constantly harbors. Saliva as well as mu- 

 cus is weakly antiseptic. Hairs grow on the lining of the nasal 

 passages and act as a coarse filter which strains dust particles 

 from inhaled air. This dust may then be expelled from the nose. 

 There are specialized epithelial cells in the windpipe and bron- 

 chial tubes with numerous cilia on their free surfaces, which 

 wave and fan bacteria or very fine dust particles up and out. 

 The foreign particles are then coughed out of the throat. 



The gastric juice in the stomach probably digests many bac- 

 teria with the food. The acid of ga-stric juice sometimes destroys 

 or inhibits the growth of many germs. Such bacteria then pass 

 on through the canal with the food. The high acidity in a dog's 

 stomach will kill bacteria that will cause intestinal infections in 

 man. Tuberculosis, typhoid fever, and dysentery germs are not 

 affected by the action of gastric juice and will pass into the small 

 intestine. Bacteria of putrefaction are always abundant in the 

 large intestine. If they are too active, intestinal disturbances 

 result. Most bacteria can work only in an alkaline medium ; 

 therefore to control and inhibit their activity, efforts are made 

 to introduce acids into the large intestine. The acids in most 

 foods are absorbed or neutralized before they reach the large in- 



Stepping on a tack, rusty nail, or other sharp objects may set up an infection. Tetanus has 

 been known to get into the body in this way and cause blood poisoning. 



testine. A certain bacillus, called the Lactobacillus bulgaricus, 

 is one of the organisms causing the souring of milk. When this 



