54 MORPHOLOGY 



threads of protoplasmic material run from this outer layer 

 through the interior of the cell, forming as it were a network 

 of protoplasmic threads in the center. The interstices of 

 this network contain the water, inorganic, and organic sub- 

 stances which compose the so-called cell sap. The sub- 

 stances within the ectoplasm compose the entoplasm. The 

 thickness of the outer protoplasmic layer, or ectoplasm, varies 

 in the same and different species. On the average it is thicker 

 in the old cells. 



By the well-known physical phenomenon of plasmolysis, 

 some very interesting points can be learned in regard to the 

 structure of bacteria. For instance, if a live bacterial cell 

 is placed in a solution of higher density (hypertonic solution) 

 than its cell sap, the solvents (water, etc.) contained therein 

 will pass through the layer of protoplasm next to the cell wall, 

 through the cell wall to join the liquid on the outside, and thus 

 serve to dilute the salts present in the solution. The layer 

 of protoplasm (ectoplasm) constitutes a semipermeable mem- 

 brane. The cell wall is permeable to most solutes, such as 

 salts, urea, sugars, etc. As a result of the loss of water by the 

 bacterial cell the protoplasm retracts from the cell wall and 

 forms itself into irregular masses within the cell. In certain 

 of the infusoria the protoplasmic layer is attached to the cell 

 wall, and the whole cell assumes an irregular shape. This 

 experiment shows that there is a definite cell wall and that the 

 protoplasm of the cell and the cell wall are distinct from each 

 other. It also serves to explain certain other bodies, such as 



