212 BARBARA LEE LUND. 



can be controlled both as to quality (a pure line of Paramecium} 

 and as to quantity if necessary. Later it was discovered that 

 an equally good control of the food of Paramecium could be 

 obtained by feeding yeast. A special study of the possibilities 

 and limits of the use of pure yeast as a food for Paramecium is 

 in progress. 



The problem of the cause of the differences in resistance to 

 the toxic action of potassium cyanide which Paramecium and 

 Didinium individuals show was chosen because it has very 

 generally been assumed that the toxic action of the cyanides on 

 other organisms is specifically due to their ability to inhibit 

 intracellular oxidations, and that differences in survival time in 

 cyanide solutions were directly due to the difference in the rate 

 of oxidations; or, as more generally expressed, "rate of meta- 

 bolism" in the organisms studied (Child, '15). Does difference 

 in resistance of Paramecia or Didinia to KCN depend upon 

 the rate of oxidations in the cell? 



The variety of types of cell suitable for studies on cell indi- 

 viduals under normal conditions is very limited. Most of the 

 information along this line has been obtained from blood cells, 

 yeast cells, echinoderm eggs and protozoa. The most extensive 

 and accurate physiological data on such questions as the nature 

 of the toxic action of the cyanides, rate of intracellular oxidations 

 and its changes in the cell during the period of cell division and 

 during the time between successive cell divisions, etc., have been 

 obtained from experiments on echinoderm eggs. It is interesting 

 therefore to see to what extent a comparison can be made of the 

 results on echinoderm eggs with those on unicellular organisms 

 during division and the changes which occur in a protozoan cell 

 between two successive divisions. For this reason I have given 

 below a brief review of the literature on the changes that occur 

 in the echinoderm egg during cleavage. 



It is important to note that the following results on survival 

 time in the solutions of KCN were obtained not by observing 

 large numbers of cells at a time, as is usual in this type of experi- 

 ment, but instead by observing one or two individuals at a time 

 and recording the survival time of each individual, so that 

 the averages given are averages of the survival times of indi- 



