CHAPTER IV 



THE BIOLOGICAL ACTIVITIES OF BACTERIA 



WHILE the bacteria pathogenic to man and animals largely usurp 

 the attention of those interested in disease processes, this group of 

 microorganisms is after all but a small specialized off-shoot of the 

 realm of bacteria, and, broadly speaking, actually of minor impor- 

 tance. Surveying the existing scheme of nature, as a whole, it is not 

 an extravagant statement to say that without the bacterial processes 

 which are constantly active in the reduction of complex organic sub- 

 stances to their simple compounds, the chemical interchange between 

 the animal and vegetable kingdoms would fail, and all life on earth 

 would of necessity cease. To understand the full significance of 

 this, it is necessary to consider for a moment the method of the 

 interchange of matter between the animal and vegetable kingdoms. 



All animals require for their sustenance organic compounds. 

 They are unable to build up the complex protoplasmic substances 

 which form their body cells from chemical elements or from the 

 simple inorganic salts. They are dependent for the manufacture of 

 their food-stuffs, therefore, directly or indirectly, upon the synthetic 

 or anabolic activities of the green plants. 



These plants, by virtue of the chlorophyll contained within the 

 cells of their leaves and stems, and under the influence of sunlight, 

 possess the power of utilizing the carbon of the carbonic acid gas 

 of the atmosphere, and of combining it with water and the nitro- 

 genous salts absorbed by their roots, building up from these simple 

 radicles the highly complex substances required for animal susten- 

 ance. 



These products of the synthetic activity of the green plants, then, 

 are ingested by members of the animal kingdom, either directly, in 

 the form of vegetable food, or indirectly, as animal matter. They 

 are utilized in the complex laboratory of the animal body and are 

 again broken down into simpler compounds, which leave the body 

 as excreta and secreta. 



The excreta and secreta of animals, however, are, in a small part 



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