1 6 ELEMENTAR Y BIOL OGY. [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 from 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.] 



