114 ^'^'^ Arthur Schacfjer 



succession; can it also make a selection from among particles that 

 are intimately mixed? And why does it at times take particles 

 that are not good for food, such as carmine? 



In the first series of experiments the following procedure was 

 adopted. In each of several small preparation dishes there was 

 placed 10 to 20 cc. of filtered fluid from the Stentor culture, to- 

 gether with about 30 S ten tors that con tamed no solid iood. Into 

 some of the dishes was introduced a mixture consisting half of 

 carmine particles, half of an admixture of Chlamydomonas with 

 some very small Euglenae. In others, serving as control carmine 

 alone was introduced, in amount equivalent to the total quan- 

 tity of particles in the other dishes. 



The contents of the dishes were thoroughly stirred, and thev 

 were then placed in a dark box to prevent the Chlamydomonas 

 from collecting at the lighted side of the dish. After half an hour 

 the Stentors were examined under the microscope. The average 

 content for each Stentor was about 1500 Chlamydomonas, about 

 85 P^uglenae, and carmine of the bulk of about 10 Euglenae. Sev- 

 eral Stentors had ingested about the same amount of food, but 

 no carmine whatever. 



About half the Stentors were left surrounded with these sub- 

 stances for 24 hours. These then contained a much greater 

 amount of Euglenae and Chlamydomonas than before, but in 

 about the same proportions. But the carmine content was prac- 

 tically nil. This is probably explained by the fact, brought out 

 in the first series of experiments, that discrimination becomes more 

 perfect as hunger becomes less. Having become in the later hours 

 nearly satisfied, the Stentors discriminated more accurately 

 against the carmine, and meanwhile that which they had ingested 

 in the first hours of the experiment had been egested in the natural 

 course of events. The result was not due to the settling of the 

 larger particles of carmine to the bottom, since when I added fresh 

 carmine, none of it was ingested. It is also improbable that the 

 Stentors had become "educated" to the fact that carmine is not 

 food, as will be shown later. 



In the control dishes where only carmine was present, the Sten- 

 tors had ingested an amount of carmine equal to about two-thirds 



