46 III. PROTOPLASMIC MOVEMENTS MIGRO. DRAWINGS. 



mic sac then again tends to expand and apply itself to the cell- 

 wall. It not infrequently happens that during the contraction 

 certain portions of the cytoplasm separate themselves from the 

 cell-body, and remain lying against the cell-wall as rounded balls. 

 These balls can also be retaken into the expanding cytoplasmic 

 sac. 



It is easy to determine that during the contraction of the 

 contents, observed as above, the colour-material does not diffuse 

 through the living cytoplasmic sac, and that the coloration of 

 the cell-sap becomes proportionally more intense. The appear- 

 ances in dead cells are quite otherwise. For example, allow 

 absolute alcohol to act upon the hairs ; the cytoplasm is imme- 

 diately killed, and now accumulates colour, for it withdraws 

 from the cell-sap the violet colouring matter, so that this soon 

 appears quite limpid, while the cell-plasm and the nucleus 

 stain deep violet. The violet colour can also pass through the 

 cytoplasmic sac, and diffuse in the surrounding fluid. 1 



The phenomena which are produced when the hairs of Trades - 

 cantia are laid in a drop of 10 per cent, solution of nitrate of 

 potash, and then taken under observation, are specially inter- 

 esting. Most of the cells, it is true, show ordinary plasmolysis ; 

 but cells will also often be found in which a barely perceptible 

 contraction of the plasmic body has ensued, whereas the cell- 

 cavity, filled with its violet cell-sap, has collected together as an 

 independent structure. In such cases the cell-plasma is quickly 

 killed, with the exception of the layer which surrounds the cell- 

 cavity. This vacuolar membrane is therefore distinguished by 

 its comparative independence and greater resisting power. At 

 length the cell-cavity forms one or several vacuoles, filled with 

 dark, violet-coloured cell-sap, lying in the disorganised cell-plasma. 

 That the plasmic layer surrounding the cell-sap remains living is 

 proved by its opposing the passage of the colouring matter. If 

 a little watery eosin has been added to the solution of nitrate of 

 potash, the dying plasma, together with the nucleus, is imme- 

 diately stained red. 



1 Living protoplasm in its active condition refuses entrance, therefore, 

 to certain stains, which, when dead, it accumulates. Various aniline colours, 

 such as methyl blue, methyl violet, cyanin, Bismarck brown, magenta, 

 safranin, methyl green, iodine green, and others, are, however, taken into the 

 living cell in a very dilute state. Living protoplasm in its latent condition, 

 exactly as when dead, absorbs stains with great avidity, as we saw in staining 

 the section of the pea (p. 28). 



