72 GORDON H. BALL. 



fatal to Paramecium. Some of the animals were capable of 

 living at least six days, and apparently indefinitely, in a dilute 

 solution (i to 125,000) of bismarck brown, the cytoplasm staining 

 a light brown, the food vacuoles taking a deeper color. Although 

 the macronucleus could be stained while the animal was still 

 actively swimming (neutral red and Janus green B), in no 

 instance was an animal so stained observed to recover. 



A dye was concentrated in the food vacuoles of Paramecium 

 and stained their contents at a strength very much below that 

 required to stain the cytoplasm. After the animals were re- 

 moved from the dye, the food vacuoles retained their color long 

 after the cytoplasm had destained. This was due also, in part, 

 to the ingestion of stained bacteria, which had been thrown 

 down by the centrifuge and transferred along with the Para- 

 mecium. It was noted particularly in solutions of neutral red, 

 where the food vacuoles continued to stain for two days after 

 the animals had been removed from the dye to fresh infusion. 

 Although nothing in the medium was visibly stained, the contents 

 of the food vacuoles took on a pink color as the latter formed at 

 the base of the gullet, and became a deep red as the vacuole 

 began passing forward from the posterior end of the animal. 

 Any observation of the time required for destaining Paramecium 

 should be based on the behavior of the cytoplasm and not of 

 the food vacuoles, which may retain their color until nearly all 

 of the bacteria in the medium have been digested. 



With all of the stains used, the color of the cytoplasm dis- 

 appeared fairly rapidly after the organisms were removed from 

 the dye solution, in no case being detectable for more than nine 

 hours, and in many instances fading out much sooner. The 

 time required for destaining the cytoplasm was independent 

 both of the length of time it had been stained and of the con- 

 centration of the dye used. If the stained animals were removed 

 to a dilute solution of the dye, their life was prolonged, but they 

 were eventually killed unless the cytoplasm destained. It is 

 possible that the results of Baldwin (1920), in which paramecia 

 so treated lived for more than eight days may have been based 

 on the retention of the dye in the food vacuoles rather than in 

 the cytoplasm proper. 



