PART I. 



MORPHOLOGY. 



CHAPTER II. 

 CELL STRUCTURES. 



The essential structures which may by appropriate means 

 be distinguished in the bacterial cell are cell ivall and cell 

 contents, technically termed protoplasm, cytoplasm. The 

 cell wall is not so dense, relatively, as that of green plants, 

 but is thicker than the outer covering of protozoa. It is 

 very similar to the cell wall of other lower fungi. Diffusion 

 takes place readily through it with very little selective action 

 on substances absorbed, as judged by the comparative com- 

 position of bacteria and their surrounding medium. 



Cytoplasm.— The cytoplasm according to Biitschli and 

 others is somewhat different and slightly denser in its outer 

 portion next to the cell wall. This layer is designated the 

 ectoplasm, as distinguished from the remainder of the cell 

 contents, the endoplasm. When bacteria are suddenly trans- 

 ferred from a given medium into one of decidedly greater 

 density, there sometimes results a contraction of the cyto- 

 plasm, due to the rapid diffusion of water. This phenomenon 

 is designated plasmolysis (Fig. 18), and is similar to what 

 occurs in the cells of higher plants when subjected to the 

 same treatment. This is one of the methods which may be 

 used to show the different parts of the cell just described. 



If bacteria are suddenly transferred from a relatively 

 dense medium to one which is of decidedly less density, it 



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