68 



ADVANCED PHYSIOLOGY 



cannot always be mischievous. They are found in the soil 

 under our feet, in the air we breathe, in the water and milk 



we drink, in much of the 

 food we eat; Fig. 32. They 

 are on our clothing, on our 

 skin, m our mouths and 

 stomachs (Fig. 33) ; there 

 are countless millions in 

 the intestine of every 

 healthy person. 



Beneficial Bacteria. 

 Although bacteria are 

 very small and are very 

 simple organisms, thei 

 are many different kinds 

 FIG. 32. A BIT OF DECAYING MEAT known; and while some 



Highly magnified, showing the bacteria that are injurious, the 



cause its decay. 



majority are harml 

 and some are even beneficial, One of the ways in which 

 they are of value to us is through their power of causing 

 all sorts of putrefaction and decay. 

 This may not seem to be either 

 useful or desirable. Putrefying and 

 decaying material is disagreeable 

 and its odor is unpleasant, but 

 the process is really one of great 

 value, for it is nature's way of de- 

 stroying the dead bodies of animals 

 and plants, which would otherwise 

 accumulate, covering the ground 

 and filling the streams. The 

 bacteria of the air, ground and 

 water attack and consume all such 

 materials. As they consume them 

 they produce gases which give the unpleasant odors to the 



FIG. 33. BACTERIA FROM A 

 HEALTHY MOUTH, MAGNI- 

 FIED 



