ON THE FEEDING HABITS OF AMEBA 571 



was no sign of the formation of a food cup the behavior of the 

 anieba must nevertheless be considered as the first part of a feed- 

 ing reaction, which remained uncompleted because of insufficient 

 stimulation from the test substance. 



The general result of the experiments with india ink was 

 changes in behavior such as are produced by carmine, but they 

 were less intense and less definite. India ink, like carmine, was 

 sensed at a considerable distance, and in nearly every case pro- 

 voked a positive reaction. 



Uric acid. The principal properties of this substance, as far 

 as relates to the purposes of this paper, are these: it is only 

 sUghtly soluble, about one part in 40,000 of water at 18°C.; it 

 is a definite chemical compound; it exerts very slight, if any, 

 injurious effect on protoplasm by lying in contact with it. 

 Merck's product was used. 



A small grain of uric acid which was placed directly ahead in a 

 granular ameba's path, produced a positive reaction — 1023. After 

 the ameba came into contact with it a food cup was formed over 

 the uric acid and a flagellate which was hovering near it. The 

 ameba then quieted down for about two minutes, after which it 

 moved off in the previous direction. About six minutes after 

 ingestion the uric acid was excreted. A few minutes later an- 

 other grain of uric acid was laid in the ameba's path — 1034. The 

 ameba at once moved into contact with it and ingested it with 

 the formation of a large food cup. About six minutes later the 

 uric acid was excreted. 



In another experiment — 1115 — in which another ameba from the 

 same culture was used, uncertain behavior was observed; that is, 

 there was first a slight negative reaction, then a positive, then a 

 negative, then again a positive, all these reactions resulting in 

 partial encircling of the uric acid granule. The ameba finally 

 moved off through a pseudopod on the right, but there was con- 

 siderable uncertainty into which of the two pseudopods on the 

 right of the encircling pseudopod the protoplasmic current was 

 to flow. When the uric acid granule was presented for the sec- 

 ond time — 1123 — the reaction was negative, there being only two 



