Protozoan Studies 269 



would cause the contraction of only a small area. Beyond the 

 contracted area the protoplasm would continue moving toward the 

 food and surround it from the sides. Probably many other factors 

 enter into and complicate the process and sometimes make it 

 resemble the food taking of higher animals. 



2. THE EFFECTS OF CENTRIFUGAL FORCE ON PARAMCECIUM' 



Methods 



For short periods of time the haematocrit attachment of a hand 

 centrifuge was used. For longer periods I made an electric cen- 

 trifuge. I made several centrifuges that could be run by a one- 

 fortieth horse power or a one-twentieth horse power hot air motor. 

 The University of Missouri furnished me with a Bausch and Lomb 

 electric centrifuge with a special revolving arm of 158 mm. radius, 

 carrying two one-half drachm vials. I enclosed this in a close 

 fitting chamber which increased the speed by preventing radial 

 air currents. With shunt winding 4000 revolutions per minute 

 were obtained. The speed was regluated with a circular rheostat 

 having 32 stops. In most cases I used gum arabic (or other 

 gums) dialysed through filter paper until it was neutral to litmus, 

 to buoy up the Paramcecia in the centrifuge, and I repeated these 

 experiments without gum up to as high a speed as the Paramoecia 

 could survive. For a convenient index of the centrifugal force 

 the formula n^r was used — ^where n is the number of revolutions 

 per minute and r the radius in millimeters. In earlier experi- 

 ments the revolutions could not be counted with a speed-counter 

 and had to be calculated from the gear, and the results were prob- 

 ably too high owing tos lipping of bands. The word outward is 

 used to denote direction from the axis of the centrifuge and inward 

 toward the axis. The recorded experiments are on Paramcecium 

 caudatum but Paramcecium aurelia gave simular results. 



For permanent preparations I found the best method to be fix- 

 ation for one minute in i per cent chromic acid and staining from 

 three to five minutes in Biondi's methyl green, orange G and acid 



'These experiments were carried on during the session of 1 906-1 907 at Randolph-Macon College, 

 Ashland, Va., and continued during the winter of 1907-1908 at the University of Missouri. 



