7O GORDON H. BALL. 



the living animal in acid or in alkaline solution. It does produce 

 a peculiar blistering of the pellicle, which, in the majority of the 

 organisms, first appears at the anterior end. Somewhat later, 

 blisters occur laterally and posteriorly, although in a few para- 

 mecia, they may arise at the posterior end before or at the same 

 time that they appear anteriorly (cf. Child and Deviney, 1926). 



Eosin did not stain the living Paramecium at any concentration, 

 nor did it stain the dead organisms for several hours at a strength 

 of i to 55 up to i to 200, even though the cell-membrane had 

 burst and the animals were cytolized. At a greater dilution 

 i to 300 or more the cytoplasm and the macronucleus quickly 

 took up the stain. 



Trypan blue or trypan red did not stain the cytoplasm of 

 living Paramecium up to a concentration of i to 155, practically 

 the maximum concentration possible. These two dyes, when 

 ingested, will color the food vacuoles but not the cytoplasm, 

 the vacuoles destaining, however, within three hours after the 

 organisms are removed from the dye. According to Rohde 

 (1917), trypan red stains Paramecium in an acid medium, but 

 the animals of this clone did not stain with trypan red or trypan 

 blue either in an acid or in an alkaline solution. Becker (1926) 

 could not stain Opalina in trypan blue or in trypan red i to 

 10,000 or i to 20,000. 



Although congo red did not stain the living cytoplasm, the 

 food vacuoles took up the stain readily, even at a dilution of 

 i to 300,000. 



Table II. is a record of those dyes staining living Paramecium; 

 they all belong to the basic group. Of these, the most suitable 

 are bismarck brown, methylene blue, methylene green, neutral 

 red, and toluidin blue. Except in highly toxic concentrations, 

 anilin yellow and methyl violet stain the cytoplasm only very 

 lightly, the color disappearing rapidly after the animals are 

 removed from the dye. Safranin and basic fuchsin stain the 

 cytoplasm only at strengths which are rather highly toxic, 

 although the latter stains the contents of the food vacuoles very 

 deeply in non-toxic concentrations. 



With the exception of bismarck brown, all of the dyes employed 

 in sufficient concentrations to stain the cytoplasm were eventually 



