THE INTIMATE STRUCTURE OF THE CELL 1S7 



the Epping Forest, near London, and in autumn imparts a 

 red coloration to the water. 



Outer protoplast. — The cell is apparently delimited on the 

 outside by what appears to be a membrane, but as it reacts 

 to stains in the same way as the rest of the cell, it must be 

 regarded as the outer somewhat denser part of the protoplast. 

 Its living nature is indicated by the attachment of the cilium 

 to it ; if it were not living, one living part of the organism 

 (the cilium) would be completely separated from the remainder. 

 On physiological grounds this is impossible. 



It is possible to detach the two protoplasts by treatment 

 with a saturated solution of picric acid for two weeks, when 

 the outer part expands, as shown in Fig. 52^. By further 

 treatment with weak methylene blue, the connection of the 

 cilium with the outer protoplast is made evident. Further, 

 during this procedure the inner protoplast contracts slightly, 

 and assumes a rounded shape, as is shown in Fig. 52 h and /, 

 leaving the outer protoplast as a delicate loosely folded 

 covering. 



When the cell is pressed gently downwards, what appears 

 to be a darker layer at the periphery of the outer protoplast 

 disappears, an added proof that there is no real membrane at 

 the periphery of the organism, and that what appears to be 

 a membrane is due to the manner in whicli the light falls on 

 the edge of the organism. The pressure of the cell causes a 

 rearrangement of the light, and the " membrane " disappears. 



The slime layer is from iju. to 2/x in thickness. A distinguish- 

 ing feature of the structure of this organism is the occurrence 

 in the outer plasma of one or two gaps filled with slime (Fig. 

 52a, e, /). They occur in any part of the cell and may be 

 together, or separated by the length of the cell. Although 

 exceptionally there may be only one of these gaps, usually 

 there are two, and apparently their number never goes beyond 

 this. Each is about 4/Li — 6/x. in diameter and oblate-spheroidal 

 in shape (Fig. 52^). As at such parts of the cell the inner 

 plasma is separated from the outside only by a layer of slime 

 it is possible to cause the inner plasma to project through these 

 slime areas by setting up differences of pressure inside the cell. 



