1896.] MICROSCOPICAL JOURNAL 269 



animal ? Locate two contractile vacuoles; wliat is tlieir 

 rytlim ? Do both contract at once ? (Tliere is a cen- 

 tral rod-shaped nucleus not easily seen in living ani- 

 mals.) In looking through large numbers of P. you are 

 sure to find some in the act of fission; such should be 

 carefully drawn and followed through the process. 



11. Action of Reagents on Paramaecium. — Irrigate 

 a mount of Paramaecium with iodine, it will kill the ani- 

 mal, at once arresting the cilia and showing them clearly. 

 By its action on the body it will demonstrate its proto- 

 plasmic nature. It may also demonstrate the nucleus, 

 but not if the specimen is too thick. Irrigate another 

 mount with 5 per cent acetic acid: this may enable you to 

 see the nucleus, 



12. Potency of Drugs as Tested on Paramaecium. 

 — Examine Paramaecium in a watch glass, I. p ,* watch 

 the motions and try to decide whether they seem to in- 

 dicate control on the part of the animal, automatis7)t. 

 Add a drop of a known strength of corrosive sublimate 

 to a known amount of fluid containing Paramaecium and 

 ascertain whether it is fatal to Paramaecium. If it is, 

 repeat the experiment, using a weaker solution of the 

 corrosive. Keep this up till you determine the per-cent- 

 age of corrosive in water which is just barely fatal to 

 Paramaecium. Determine the same percentage for acet- 

 ic acid, also for alcohol. Can you infer that drugs have 

 varying power to affect cells? 



13. Vorticella. — Search on the threads of fresh-water 

 algae for Vorticella, study the colony I. p. and then study 

 individuals, ^. ^., distinguish the long slender contractile 

 stem attached below and bearing on its summit the bell- 

 shaped body; locate the peristome or rim of the bell, and 

 determine that it is ciliated; do you find cilia in any 

 other part of the body ? Note the epistome closing the 



* 1. p. and h. p. indicate low and high powers respectively. 



