CHAPTER IV 



CHANGES OF ECONOMIC SIGNIFICANCE BROUGHT ABOUT BY 

 NON-PATHOGENIC ORGANISMS 



MICROORGANISMS bring about many changes, both analytic 

 and synthetic, in the media in which they are cultivated. In 

 any such medium growth products of many kinds will be found. 

 These fermentative products may originate from the activity of 

 extracellular enzymes, may consist of substances excreted from 

 the cell as the product of intracellular enzymes, or as a result 

 of the metabolic activity of the cell; they may be products of syn- 

 thetic action (as the slimes and gums produced by a solution of 

 the bacterial capsule), or they may be substances produced by the 

 autolytic activity of intracellular enzymes after the death of the 

 cell. Naturally, the products will vary greatly with the species 

 of organism, the medium in which it is grown, and the character 

 of the physical environment. 



From the standpoint of the veterinarian, microorganisms 

 are of most importance because many of them produce disease. 

 It would, however, give a false impression of the place and function 

 of microorganisms in nature to neglect at least a brief consid- 

 eration of some of the other changes which they can bring about. 

 In this chapter some of the more important will be considered. 



The well-nigh universal distribution of bacteria and other 

 microorganisms should be emphasized. They are to be found in 

 the soil in great numbers, rich surface soil containing from 100,000 

 to 5,000,000 bacteria to every dry gram. Their dried bodies and 

 spores are constantly present free or attached to dust particles in 

 the air. They are to be found in all surface waters in considerable 

 numbers and are present even in the water from deep wells. 

 They grow upon the surface of the skin of animals, and the mouth 

 and digestive tract support a large and varied flora. It is apparent 

 that whenever conditions are favorable for the growth of micro- 

 organisms they will be present to begin growth. 



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