CHAPTER IV. 



RANGE AND DISTRIBUTION OF MICROBES. 



Microbes are omnipresent over the surface of the earth. In number and 

 in bulk they exceed all other organisms (plants and animals) put together. 

 They form a large precentage of the bulk of the soil. They occur in the air, 

 in water, in snow, in hail, in raindrops, in and upon plants, in and upon 

 animals. All substances with which we come in contact are likely to hold 

 microbes. Our clothing teems with them. They are in the air we breath, 

 in the food we eat, and in the liquids we drink. The floating dust particles 

 of the air carry microbes; the particles of organic matter in water harbor 

 microbes; they are found on wood, on cloth, on paper, on metal, glass, and 

 rock surfaces, in fact on all exposed surfaces. The hands, the hair, the 

 entire body surface of man and of the lower animals contain or hold mi- 

 crobes. They line all mucous membranes. The mouth cavity is a veritable 

 bacteriological laboratory. The entire intestinal tract teems with millions 

 upon millions of these minute beings. 



Each animal and each plant has a microbic flora peculiar to itself. Each 

 portion of the plant or animal, again, has distinctive bacterial groups. The 

 microbic flora of the intestinal tract of the dog is different from that of the pig, 

 or cat, or fowl, or man. Certain species predominate in the mouth cavity, 

 others in the stomach, still others in the small intestine, in large intestine, etc. 



Microbes are found on the highest mountain peaks and in the deepest 

 valleys. It is, however, true that the higher atmospheric strata contain 

 fewer microbes than the lower strata. The deeper layers of soil contain 

 fewer microbes than the upper. The atmosphere of the country contains 

 fewer microbes than that of the cities and towns. Since sunlight and 

 absence of moisture are natural enemies of microbes, we may expect to find 

 microbes more abundant in dark, damp, and moist places and areas. Mi- 

 crobes are always more abundant in cellars, basements, dark hall-ways, and 

 alleys than they are in attics, sunlit living rooms, and along broad boule- 

 vards and highways. 



Good drinking water, whether from hydrant, spring, or well, contains only 

 a comparatively few microbes, from fifty to one hundred per c.c., or even less. 

 Stagnant, foul water teems with microbes, besides other organisms, such as 

 protozoa. So-called pure milk contains comparatively more microbes than 

 pure water. The average good milk contains as many as 30,000 microbes 



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