Food Selection Among Lower Animals. 37 



crimination was exhibited when a mixed stream of several differ- 

 ent kinds of indigestible particles and several different kinds of 

 organisms were fed. 



After it was clear that stentor can discriminate between food 

 substances and indigestible particles, the question arose whether 

 stentor selected certain food organisms in preference to other 

 food organisms. To determine this, several different kinds of 

 food organisms were fed in mixed order. At first all the differ- 

 ent organisms were eaten, but as the stentor became less and less 

 hungry, one kind after another of the organisms were rejected 

 until some little time before the stentor was satiated, only one 

 kind of organism was eaten. These various food organisms, while 

 they differed but slightly in size, varied greatly in shape of body. 

 The results of these experiments interested me to the extent that 

 I desired to see how delicate the sense of discrimination is in 

 stentor. To test this, I was fortunate in having cultures of two 

 kinds of small organisms that were not closely related, but were 

 almost exactly alike in size and shape. It required a trained eye 

 to tell the difference between them. These two kinds of organ- 

 isms were mixed in equal numbers and fed to the stentor one by 

 one. At first both kinds of organisms were eaten. As the sten- 

 tor became less and less hungry, many of both kinds of organisms 

 were rejected. But finally when nearly replete, only now and 

 then would an organism be eaten, and it is very remarkable to 

 observe that all the organisms eaten when hunger had nearly dis- 

 appeared, zvere of one sort ; the organisms of the other sort were 

 all rejected. 



We may conclude then that stentor discriminates in food with 

 a degree of precision that is matched only, so far as we know, by 

 that of the higher animals. And the observation that stentor dis- 

 criminates more and more precisely as hunger grows less, is also 

 paralleled in the higher forms. Even in man does this observa- 

 tion hold. When hungry almost any kind of food is eaten, 

 but when hunger has nearly vanished, only such things as 

 desserts are capable of stimulating the eating mechanism. There 

 is therefore a remarkable degree of similarity in the feeding be- 

 havior of the highest animals and of stentor. 



The ability to discriminate in a high degree having been shown 

 to exist, the question arises : How is it effected ? Since stentor 



