CHAPTER III 

 THE MORPHOLOGY OF MICROORGANISMS 



The cell. The unit of life is the cell, which consists of a 

 limiting membrane inclosing semi-liquid contents. Within 

 the cell are carried on all of the activities of the organism : 

 herein the food is assimilated, by-products are formed, and 

 energy is liberated for all of the vital processes. 



The higher plants and animals are constructed out of 

 great numbers of these unit cells, which, however, are col- 

 lected into groups that are so related to each other as to 

 form tissues. These tissues are often so differentiated in 

 their physiological activity that they may perform a limited 

 and highly specialized function. With the simpler forms 

 of life, such as the bacteria, all of the complicated chemical 

 processes essential to the life of the organism take place 

 within the limits of a single cell. Between the two ex- 

 tremes there are to be found organisms in all degrees of 

 complexity as to structure and function. The types that 

 are of greatest importance in the decomposition of organic 

 matter are either unicellular or the simpler multicellular 

 forms. 



With the multicellular organisms, variation in structure 

 of the individual is limitless; consequently, morphology, or 

 the science that describes the variation in form, is of major 

 importance. The simplicity of the one-celled plants, the 

 bacteria, and the yeasts, makes a description of their mor- 

 phology much less complex. 



The division of life into plants and animals, so advanta- 

 geous in the study of the higher forms, is not especially help- 



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