CHAPTER III 



PHYSIOLOGY OF MICROORGANISMS 



PHYSIOLOGY has been defined by Barnes to include " a study 

 of the behavior of plants (and animals) of all sorts, and of the 

 ways in which this is affected by external agents of every sort." 

 In our discussion of the physiology of microorganisms we shall 

 have to deal principally with the interrelationships existing 

 between these microorganisms and their environment. 



FOOD RELATIONSHIPS OF MICROORGANISMS 

 A food is any substance which a living organism may make 

 a part of its living material or use as a source of growth energy. 

 The term is frequently used very loosely to include all the sub- 

 stances of which an organism may make any use. For example, a 

 distinction is sometimes made between green plants and animals 

 on the basis of food used. The former are said to live on inorganic 

 foods and the latter on organic. This distinction is erroneous. 

 The difference is simply that green plants can manufacture their 

 own foods out of inorganic material by the aid of the energy 

 secured from the sun's rays through the green coloring-matter or 

 chlorophyll, while animals make use of food already prepared. 

 The materials of which some microorganisms make use are no more 

 foods than the rays of the sun are a food for green plants. 



Composition of the Cell. The food utilized by any micro- 

 organism must contain the elements needed for the building up 

 of the cell substance. The analysis of such cells shows them 

 to be made up of the same elements as those of higher plants 

 and animals, namely, carbon, oxygen, nitrogen, hydrogen, and 

 smaller amounts of phosphorus, iron, magnesium, calcium, and 

 some other elements. The foods utilized by organisms must, 

 therefore, contain these elements likewise. 



Sources and Kinds of Foods. Some bacteria, like the green 

 plants, are capable of manufacturing their own food. For this 

 purpose a source of energy is necessary. Some species utilize the 



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