CHOICE OF FOOD IN AMEBA 233 



an apple from among some oranges, by a kinematograph with- 

 out the use of a word. But would the general impression on 

 the mind be any different, i.e., would it be devoid of subjective 

 elements? It is just as anthropomorphic to say that the ameba 

 eats globulin and leaves carbon, as to say, the ameba expresses 

 choice between globulin and carbon (eating the former and not 

 the latter). 



Briefly then, the word choice serves for two purposes. First, 

 it is used as a hypothesis, as a tool of research. It postulates 

 a certain kind of relation which is to give direction to investiga- 

 tion. All except haphazard investigation proceeds in this man- 

 ner. Second, its use is indispensable for brief and intelligible 

 description; but any subjective connotation which the word may 

 call forth should be disregarded by the reader unless the author 

 specifies definitely otherwise. It is in this latter sense that the 

 word is used in the descriptions in this paper. 



In a former paper ('10) I demonstrated that the ciliate stentor 

 is capable of exercising very nice discrimination among the 

 various particles which are carried to its mouth by its cilia. 

 Not only is the discrimination between food and indigestible 

 particles (excepting carmine) very precise, but even among food 

 particles themselves, certain organisms being eaten and others 

 rejected. This is particularly noticeable when the stentors are 

 partially satiated. 



Now ameba discriminates with equal or perhaps greater pre- 

 cision. Excepting carmine, no indigestible substances are eaten 

 unless agitated. Of the various things eaten, living organisms, 

 such as flagellates, coleps, etc., come first in point of preference. 

 Then comes globulin, grain gluten, carmine, and tyrosin. Less 

 attractive than these are: aleuronat, fibrin, lactalbumin, oval- 

 bumin and keratin, and peptone in solution. Digestible sub- 

 stances that are eaten only occasionally are soluble egg white, 

 solid egg white, uric acid. No starch, lecithin, silicic acid, 

 carbon (excepting in one case), sodium chloride, iron, choles- 

 terin, etc., were eaten unless agitated. Sand grains were never 

 eaten under my observation, and I have never seen " numerous ' 

 sand grains inside of amebas from wild or laboratory cultures. 

 It will be recalled that sand grains are frequently referred to in 

 text books and elsewhere as " typical " contents of the ameba's 

 body. 



How can these preferences be explained? As far as can be 



