242 A. A. SCHAEFFER 



and unicellular algae, it takes algae, but when feeding on algae 

 it will leave them to ' pursue ' ciliates. In the presence of 

 large paramecia, some amoebas leave algae and ciliates to catch 

 these larger forms. Amoeba eats nothing dead. This was 

 observed in the case of dead diatoms and algae cells, of paramecia 

 dead from natural causes, and of paramecia which had been 

 artificially killed. Amoebas do not apparently eat their own 

 species, but were seen to eat amoebas of other species " (p. 240). 



As we have seen, however, A. dubia eats lifeless things, though 

 only very rarely (see under carmine, Schaeffer, '16a, '16b under 

 ' raptorial ' amebas) . My observations confirm theirs on ' 

 reactions toward dead organisms or parts of organisms: none 

 are eaten. Now when it is remembered that in the normal 

 life of an ameba neither carmine nor isolated proteins occur, 

 it is clear that movement in an object is practically the only 

 quality which induces feeding in A. dubia. In other words 

 we have conclusive proof that the chemical nature of the moving 

 eaten object is of no importance whatever in so far as feeding 

 is concerned, and that the quality that actually determines 

 ingestion is clearly a physical quality. The ability to discrimi- 

 nate among substances on a chemical basis while feeding, might, 

 therefore, be entirely absent in A. dubia without affecting its 

 ability to live successfully. 



So far as normal feeding is concerned, A. proteus has prac- 

 tically the same habits as A. dubia, in that by far the larger 

 quantity of food consists of living moving organisms, which 

 are selected because of their movement. But it differs from 

 A. dubia in that dead organisms and fragments of isolated 

 proteins, etc., are readily eaten. Here, manifestly, selection is 

 made upon a broader basis. But if all the experiments where 

 motionless objects are eaten are taken together it does not seem 

 possible as we have already seen that choice based upon a single 

 factor could lead to such diversified behavior. Thus if the 

 chemical nature of substances stimulated ingestion (1) carmine 

 would probably not be eaten; (2) solid and soluble egg albumin 

 and gelatin would probably be eaten with avidity; (3) globulin, 

 lactalbumin, ovalbumin, which are said to be insoluble, would 

 be eaten; (4) uric acid would not be eaten; (5) capillary tubes 

 filled with carmine solution and with tyrosin solution would be 

 as attractive as solid carmine and tyrosin respectively; (6) food 



