STUDIES OX PARAMKCIUM. 75 



According to Packard (1925), light increases the permeability of 

 the protoplasm of Paramecium; the greater toxicity is not solely 

 a matter of permeability, however, since such stains as neutral 

 red penetrate the cytoplasm almost immediately, yet the animals 

 live twenty times as long in the dark as under strong illumination. 

 Child and Deviney (1926) noted greater toxicity of eosin, neutral 

 red, and methylene blue for Paramecium upon exposure to light, 

 while Baldwin (1920) found that stained paramecia were more 

 susceptible to X-rays than unstained ones. In the clone used 

 in the present experiments, long contact with the dye does not 

 produce any acclimatization on the part of the Paramecium; 

 animals kept in the dark in neutral red I to 125,000 or in 

 methylene blue I to 100,000 for eighteen hours die just as soon 

 under strong illumination as those exposed to the light and the 

 stain simultaneously. Furthermore, merely subjecting the dye 

 to intense light does not make it more toxic when subsequently 

 added to cultures of Paramecium. 



DISCUSSION. 







The literature on vital staining in the Protozoa has been well 

 reviewed by Nirenstein (1920) and by Vonwiller (1921), and 

 consequently will not be considered here. 



All of the dyes which stained the cytoplasm of normal living 

 Paramecium belonged to the basic group. None of the acid 

 dyes stained the cytoplasm of normal animals, although most 

 of them stained the dead or dying organisms. Lyons blue was 

 the only basic dye not staining the living animals. There have 

 been many different interpretations of the meaning of the 

 reactions taking place between different dyes and living proto- 

 plasm (Nirenstein, 1920). If it be concluded from the above 

 results that, under normal conditions, the protoplasm of Para- 

 mecium is acid in reaction, this would confirm Crozier's obser- 

 vation (1923), using brom thymol blue as an indicator, that the 

 pH of the living protoplasm of Paramecium is 6.7 or less, and 

 not alkaline or neutral as is usually maintained. 



The period required for destaining the organisms was in- 

 dependent both of the length of time necessary for staining 

 them, and of the concentration of the dye used. Furthermore, 



