REACTIONS OF AMEBA TO PROTEINS 79 



Keratin, fibrin, aleuronat and grain gluten are also eaten by 

 amebas; the first two occasionally, the last two frequently. 



2. Isolated proteins are sometimes ingested in food cups of 

 varying size, sometimes without the formation of food cups. In 

 the latter case the protoplasm merety flows around the food par- 

 ticle. Occasionally a food cup is started before the ameba comes 

 into physical contact with the protein particle. 



3. Granular amebas eat isolated proteins much more fre- 

 quently than the raptorial, and they retain what they eat much 

 more readily. 



4. It cannot be stated what qualities in these proteins induce 

 ingestion. The fact that the one which is probably the most 

 readily purified, zein, is not eaten, may indicate that perhaps 

 minute traces of soluble material are present in globulin, lac- 

 talbumin and ovalbumin. It is also possible that these proteins 

 are very slightly soluble in the water in which amebas live. 



5. From the point of view of general behavior several facts 

 are brought to light. 



a. An ameba utilizes the vestige of a former pseudopod for the 

 projection of a new one whenever it is possible rather than form 

 an entirely new pseudopod. The reactions of an ameba at a 

 given time are, in a definite manner and to a large extent, con- 

 ditioned by its behavior, that is, by changes in the shape of its 

 body, during the preceding minutes. 



b. There is a large amount of objective evidence that positive 

 and negative tendencies of reaction with respect to a single 

 source of stimulation are effectively present in ameba, and that 

 reactions are not due in any sense to the direct effect of the 

 stimulus. 



POSTSCRIPT 



After this paper was in manuscript the species reference of 

 'raptorial' and 'granular' amebas was investigated. The granular 

 amebas were found to be of two species: Amaeba proteus 

 Pallas emend. Leidy, and A. discoides Schaeffer; the raptorial 

 of one species A. debia Schaeffer. See my paper in Science, 

 September, 1916 for descriptions of these species. 



