16 ELEMENTARY BIOLOGY. [CHAP. n. 



/?. Cells much like the above if the cellulose 

 sac were removed, and the radiating processes 

 extending to it from the protoplasm with- 

 drawn. 



b. Try to find specimens in which the movements 

 are becoming sluggish, and see the cilia in 

 motion. 



c. Stain with iodine : this kills the cells, and stops 



their movements ; and frequently renders the 

 cilia very distinct. 



[B. PHYSIOLOGY. 



Get some water that is quite green from containing a 

 large quantity of Protococcus ; introduce some of it 

 into two tubes filled with and inverted over mercury, 

 and pass a small quantity of carbonic anhydride into 

 each : keep one tube in the dark and place the other 

 in bright sunlight for some hours. Then measure the 

 gas in each tube and afterwards introduce a fragment 

 of caustic potash into each ; the gas from the specimen 

 kept in the dark will be more or less completely ab- 

 sorbed (= carbonic anhydride), that frpm the other 

 will not be absorbed by the potash alone, but will be 

 absorbed on the further introduction of a few drops of 

 solution of pyrogallic acid ( = oxygen). Protococcus, 

 therefore, in the sunlight, takes up carbonic anhydride 

 and evolves oxygen. A comparative experiment may 

 be made with a third tube containing water but no 

 Protococcus.] 



