1 6 BACTERIA AND SOIL FERTILITY 



tenth and seventeenth hour they have reached the intestines. From 

 the minute of birth until the time of death it is a constant struggle 

 betv^een the individual and the microbes. And one individual 

 has jokingly remarked, "Microbes get us at last." This is strictly 

 true, for most individuals die of bacterial diseases long before the 

 allotted three-score-and-ten years have elapsed. Even those 

 who die from accident or old age, their bodies, unless cremated, 

 are decomposed by bacteria. 



Ordinarily, the deeper respiratory passages contain few bac- 

 teria, but it has been proven that at times even the tuberculosis 

 organism can penetrate with the inspired air to the bottom of the 

 lungs. 



On account of its acidity, yeasts and molds flourish better in 

 the stomach than do bacteria. However, at least thirty different 

 kinds of bacteria have been described as occurring in the stomach. 

 Many of these have attracted special attention on account of the 

 belief that their presence may favor or retard other more injuri- 

 ous species. 



The intestines on account of their alkaline reaction and the 

 partly digested condition of their contents are a great reservoir 

 of bacterial activity. In the upper part there are few, but by 

 the time the descending colon is reached billions of bacteria are 

 often present. Sometimes they constitute one-third of the total 

 dry contents of the intestine. The health of the individual is 

 determined by the number and kind of bacteria, and at least one 

 writer has suggested that our very personality is governed by the 

 microbes we carry about with us. 



The normal tissues of plants and the blood of animals are free 

 from bacteria. They are rarely found on certain healthy mu- 

 cous membranes, such as those of the kidneys, bladder, and lungs. 

 Occasionally they pass through the skin or mucous membrances of 

 the digestive tract, after which they may be found for a short 

 time in the blood. This is especially true during the height of 

 digestion, and we £nd at this time large numbers of white cor- 

 puscles swarming into the intestinal mucosa ready to pick up and 

 devour any bacteria which may enter. In this manner the body 



