198 SCIENCE FROM AN EASY CHAIR 



they are introduced, are stained with an alkaline blue 

 such as blue litmus, they are seen in the course of a few 

 seconds to turn red showing that an acid has been 

 secreted by the protoplasm (probably accompanied by 

 a ferment) into the little sphere of water, in which the 

 digestion of the boiled bacteria now goes on. In the 

 course of a few minutes you will see the little sphere of 

 water dwindling in size the nourishing liquid being 

 absorbed by the protoplasm and then you will see 

 the undigested fragments passed on by a slow movement 

 to the vestibule or " pit " of the mouth, extruded through 

 a temporary opening from the protoplasm, and whirled 

 away by the water currents ! If you colour the " boiled 

 bacteria " with water-soluble anilin-blue as I did many 

 years ago you will see that the colour vanishes 

 from the particles taken into the bell-animalcule's 

 protoplasm, and presently an independent sphere of 

 bright blue liquid begins to form in the protoplasm. 

 This sphere or globule is the renal organ mentioned 

 above here very simple and single (Fig. 40^). It is 

 called the pulsating chamber or " contractile vacuole." 

 It enlarges rapidly, filling with blue liquid (when special 

 coloured food has not been supplied the liquid is colour- 

 less), then suddenly contracts, squirting its blue contents 

 out through a special reservoir (fi) into the mouth-pit 

 (as shown by an arrow in the figure). 



The nucleus of these unicellular animals is often 

 elongated (2), and shaped according to the general shape 

 of the animalcule ; but it is the same thing as the 

 "nucleus" of all cells, whether of plants or animals 

 a denser " kernel " of protoplasm, limited by its own 

 delicate sheath or membrane. It shows, like the cell- 

 nucleus of ordinary cells, a special affinity for certain 

 dyes, which do not stain the rest of the cell, so that it 

 can be made very obvious and clear when the animalcule 



