CHAPTER V 



PHYSIOLOGY OF MICROORGANISMS 



In a general way, the simple presence of microorganisms 

 has no significance, as far as the decomposition of organic 

 matter is concerned. Decomposition always implies the 

 growth, the proliferation, of the organism. Two problems 

 present themselves daily to almost every individual. One 

 is connected with the prevention of the growth of organ- 

 isms in order that organic materials may be preserved ; the 

 other is the facilitation of the growth of organisms in order 

 that the chemical change that they cause may be hastened. 

 The conditions favoring or retarding the growth of micro- 

 organisms thus become of great practical importance. 



Moisture. Water is an essential condition for the de- 

 velopment of all life. It makes up a large part of the 

 weight of every organism; it is needed for the transporta- 

 tion of the food and waste products. It is impossible to 

 make any general statement in regard to the amount of 

 water that must be present before growth can take place. 

 Some types of materials hold water in such a way that the 

 organisms can not make use of it. The material is then 

 said to be physiologically dry. Bacteria can grow in butter 

 containing 15 per cent, of water, while they can not grow 

 in most types of organic matter unless a much greater per- 

 centage of water is present. The reduction of the water 

 content of organic matter is the most common way of pre- 

 serving it from the .attacks of microorganisms. 



The growth of microorganisms may be prevented in the 

 presence of large amounts of water by its content of mate- 



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