BEHAVIOR OF AMEBA TOWARDS VARIOUS SUBSTANCES. 325 



SUMMARY. 



1. Ameba senses small particles of insoluble substances such 

 as carbon, glass, silicic acid, etc., at a distance of from 60 to 100 

 microns. The reaction is nearly always positive and it consists 

 in the turning of the main pseudopod toward the test object or 

 in the projection of a pseudopod on the side of the main one 

 toward the object. The side pseudopod may or may not become 

 the main pseudopod. After the test object is touched the ameba 

 usually moves on without further change in behavior. 



2. Although the facts are clear, the explanation of reaction 

 at a distance to insoluble substances is lacking. Surface action 

 of some sort or the reflection of light from the test object are 

 possible factors. But whatever the explanation, the ability of 

 an eyeless animal like ameba to sense insoluble objects at a 

 distance is without parallel among organisms and it is conse- 

 quently a phenomenon of fundamental importance in sense 

 physiology. 



3. Ameba reacts positively to ty rosin. The behavior toward 

 small grains of tyrosin is very peculiar. The ameba moves 

 toward the tyrosin as if strongly attracted and begins the forma- 

 tion of a food cup. The stimuli then seem to become so intense 

 that they produce a negative effect in the reactions, and the 

 ameba withdraws from the tyrosin grain. Tyrosin grains are 

 however occasionally eaten. 



4. The reactions toward tyrosin refute completely the conten- 

 tion (if it still needs refutation) that the eating process in ameba 

 is purely a surface action effect of the stimulating object. 



5. Both egg albumin and peptone in weak solution diffusing 

 from a capillary tube cause the formation of food cups. In 

 nearly all cases the food cups were formed over the open end of 

 the tube as the solid source of the diffusing albumin or peptone; 

 but in one or two cases a food cup was formed at a distance 

 from the tube. Peptone stimulates the ameba much more 

 readily than albumin. 



6. Solutions of carmine and tyrosin in capillary tubes do not 

 readily attract amebas. This is in strong contrast to the be- 

 havior toward grains of these substances, which is almost always 

 positive. The difference in behavior as recorded is perhaps due 

 to faulty technic in handling the capillary tubes. 



