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 micro- 

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

 bacteria, and, broadly speaking, actually of minor importance. Sur- 

 veying the existing scheme of nature, as a whole, it is not an extrava- 

 gant statement to say that without the bacterial processes which are 

 constantly active in the reduction of complex organic substances 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 neces- 

 sary 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 activi- 

 ties 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 atmos- 

 phere, and of combining it with water and the nitrogenous salts ab- 

 sorbed by their roots, building up from these simple radicles the highly 

 complex substances required for animal sustenance. 



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 

 only, made up of substances simple enough to be directly utilized by 

 plants. The dead bodies, moreover, of both animals and plants would 



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