STUDIES ON PARAMECIUM. 73 



The comparatively rapid loss of the color by stained paramecia 

 indicates the ability of the protoplasm of Paramecium to reduce 

 or to eliminate the dye in a few hours; or perhaps even marks a 

 complete change of protoplasm in this time. 



A solution of I to 180,000 Janus green B shows almost im- 

 mediately a number of small rod-like bodies, probably mito- 

 chondria (Causey, 1926; Hogue, 1926). These were somewhat 

 more widely scattered through the cytoplasm than those shown 

 in Causey's figures, although they could also be detected between 

 and around the food vacuoles. The dye is exceedingly toxic for 

 Paramecium, killing them in a few hours at a concentration as 

 low as i to 450,000. The cytoplasm stains bluish green at I to 

 180,000, the macronucleus taking on a yellow color before the 

 animal dies. The food vacuoles are at first bluish green, later 

 becoming light pink due to the reduction of the Janus green B 

 to diethylsafranin. 



All of the above experiments were performed in the diffuse 

 light of the laboratory, the cultures being kept under glass, 

 out of the direct sunlight. Animals stained with certain dyes 

 (Table III.) give a very striking reaction to strong light. These 

 stained Paramecium drawn from a flourishing culture soon be- 

 come sluggish and settle practically motionless on the bottom of 

 the Syracuse watch glass. They can be observed in this condition 

 under a compound microscope with the iris diaphragm almost 

 completely closed, and a heat screen interposed between the 

 organisms and the source of light. If the diaphragm now be 

 suddenly opened, practically all of the animals begin darting 

 violently about, giving the avoiding reaction and soon swimming 

 out of the field. The reaction begins in from four to five seconds 

 after opening the diaphragm, and occurs almost simultaneously 

 in 90 to 95 per cent, of the animals exposed. If the Paramecium 

 are observed under a 16 mm. objective, the field will be entirely 

 empty in two to three minutes, even though several hundred 

 motionless animals may have been present previously. If the 

 diaphragm be closed before the field is completely vacant, the 

 remaining organisms settle to the bottom of the dish again 

 within one minute. If only the food vacuoles are stained but 

 not the cytoplasm, the animals do not exhibit these reactions to 



