76 GORDON H. BALL. 



if the cytoplasm stained at all, the color was as intense with a 

 dilute as with a concentrated solution of the stain. In dilute 

 solutions, the cytoplasm or the food vacuoles might stain deeply, 

 yet the fluid medium or the bacteria might show only a very 

 slight color. According to Nirenstein (1920), the capacity of the 

 living cell for taking up dyes depends upon the distribution of 

 lipoids in the protoplasm. It may possibly mark merely a more 

 intense staining reaction rather than an increased concentration 

 of the dye. The failure of the acid dyes to stain the cytoplasm 

 does not prove that they fail to enter as freely as do the basic 

 ones; the behavior of the organisms indicates rather that the 

 dyes of the acid group do penetrate the cell without staining the 

 cytoplasm. 



Certain dyes act as sensitizers for the destructive action of 

 light; their toxicity is not increased by exposure to strong light 

 before addition to the Paramecium cultures. The effect is not 

 solely one of greater permeability since the shorter length of 

 life in light bears no relation to the ease of penetration of the 

 dye. With this clone of Paramecium, the harmful effect of 

 light for the stained organisms began within five seconds of 

 exposure, as indicated by the behavior of the animals themselves. 



This work on vital stains was started originally in the hope of 

 employing it to mark individuals belonging to different clones 

 of Paramecium. Thus, it would be possible to determine whether 

 or not extra-clonal conjugation can be obtained under experi- 

 mental conditions. However, the rapidity with which the cyto- 

 plasm of these animals loses its color after being removed from 

 the stain precludes the use of this method as a means of identifi- 

 cation. It seems probable that we shall have to employ morpho- 

 logical differences, other than those of size, such as the notched 

 mutant recently described by Dawson (1926). 



CONCLUSIONS. 



1. The only dyes staining the cytoplasm of normal living 

 Paramecium belonged to the basic group. Those found to be 

 most suitable were bismarck brown, methylene blue, methylene 

 green, neutral red, and toluidin blue. 



2. The cytoplasm of normal animals could not be stained by 



