BEHAVIOR OF AMEBA TOWARDS VARIOUS SUBSTANCES. 311 



which the left member of the middle pair became the main 

 pseudopod. As this one moved forward with the glass particle 

 on its right, a pseudopod w r hich appeared on its right, enlarged 

 and moved directly into contact with the glass 197, 198. When 

 the pseudopod came into contact with the glass, streaming be- 

 came more rapid and the ameba flowed over the glass particle 

 and moved away. 



To summarize: The behavior of ameba tow r ard glass fragments, 

 under the conditions above outlined, demonstrates even more 

 clearly than the reactions toward pure carbon, that insoluble 

 objects can be sensed at a distance. The maximum distance at 

 which glass can be sensed, as demonstrated by experiment, is 

 about sixty microns, though it is probable that in several of the 

 experiments the amebas sensed the glass particles at 100 microns. 

 The ameba does not always react positively when glass is sensed, 

 but positive behavior is much more frequent than negative. 

 Although the ameba starts moving toward the glass particle in 

 almost all cases, it sometimes reverses the direction of motion 

 when almost in contact with it. In most cases however the 

 ameba continues moving until it comes into contact with the 

 glass, and then the behavior becomes more or less indifferent. 

 No attempt was made to eat particles of glass. 



Graphite. A grain of Merck's purified graphite was laid in 

 the path of a granular ameba 202. The ameba turned to the 

 right and moved directly toward the graphite until it came within 

 about fifteen microns of the object, when protoplasmic streaming 

 was interrupted for an instant and then directed upwards and 

 aw^ay from the graphite 207-209. The piece of graphite was 

 then shifted 210. The ameba turned to the right and away 

 from the graphite, but a pseudopod which was then sent out 

 on the convex side elongated and became the main pseudopod 

 until it came into contact with the graphite (the contact stage is 

 not figured) 214, 215. It was then slowly retracted while the 

 previous main pseudopod became active again and led the ameba 

 away. The precision of the reaction indicates that the graphite 

 was sensed at a distance of at least sixty microns. 



The effect of graphite on the reactions of ameba is similar to 

 that produced by glass. Graphite usually produces a positive 



