Selection of Food in Stentor Cceriilens {Ehr.) JJ 



Khrenberg's or Verworn's work mentioned above, where indiges- 

 tible particles were described as being freely eaten. 



Jennings in 1902 worked upon Vorticella and confirmed Ehren- 

 berg's and Verworn's experiments; he showed that Hodge and 

 Aikins' conclusions were probably drawn from insufficient data. 

 Similar experiments upon Stentor also showed that this infusorian 

 ingested large quantities of carmine, india ink, etc. From these 

 experiments Jennings came to the conclusion that these organisms 

 probably do not have the power of selecting their food in any^ pre- 

 cise way. 



In 1907 there appeared a preliminary paper by Metalnikow 

 "Ueber die Ernahrung der Infusorien und deren Fahigkeit ihre 

 Nahrung zu Wahlen," in which the author describes the taking up 

 or ingesting of carmine and india ink by paramecium, but states 

 thatif left in water in which is suspended carmine or ink, the para- 

 mecia gradually take in less and less of these substances until m 

 about 18 days few or none contain either ink or carmine. Accord- 

 ing to Metalnikow the paramecia are gradually "educated" in 

 some way so that they cease after awhile to take the carmine or 

 ink. This paper will be more fully discussed further on. 



This brief historical account includes most of the more impor- 

 tant references to the ability of protozoa to select food. These 

 references are all incidental in character and the experiments upon 

 which they were based were in almost every case few and not 

 varied. This lack of experimentation was probablv due to the 

 notion thatif they could discriminate at all, the protozoa should 

 tell with precision for each and every particle whether it is food 

 or not, and that an V mistakes would be sufficient evidence that the 

 ability to choose among particles of various sorts is absent. In 

 short, machine-like accuracy seems to have been expected if selec- 

 tion is present at all. 



But we can hardly with clear thinking demand more prelect 

 selective faculties in the protozoa than in the higher vertebrates. 

 If one should draw the conclusion that because one observes a 

 horse eat bits of a weather-beaten fence rail, the horse has not the 

 ability to select his food, the logic would be equivalent to that 

 which is used when it is affirmed that because a protozoan eats car- 



