BEHAVIOR OF AMEBA TOWARDS VARIOUS SUBSTANCES. 315 



ameba then broke up into four pseudopods, two of which were 

 directed toward the oxide 494. The ameba moved off to the 

 right without further reaction toward the oxide. 



Lead oxide induces strongly positive behavior in raptorial 

 amebas. Not only are the amebas induced to move toward this 

 substance, but occasionally the initial stages of ingestion seem 

 to be called forth by it. In this respect lead oxide stands on a 

 level with, or above, some food substances such as zein or oval- 

 bumin. In strong contrast to the behavior of raptorial amebas 

 toward lead oxide is that of the granular amebas. In these, 

 negative behavior is nearly always produced by this substance. 

 Why there should be this difference is not clear. The solubility 

 of this substance was not tested by me. 



Among other insoluble substances that were used in these 

 experiments is iron. This metal cannot be obtained perfectly 

 pure and it also undergoes chemical action in the water. Par- 

 ticles of it were agitated by means of an electromagnet beneath 

 the stage of the microscope, but the apparatus was rather crude 

 and no definite results were obtained. 



REACTIONS TO VERY SOLUBLE DIGESTIBLE SUBSTANCES. 

 Substances belonging to this class, such as gelatine and tyrosin, 

 are much less satisfactory to work with than those substances 

 that are insoluble, or only very slightly soluble; for the stimuli 

 proceeding from very soluble substances cannot be definitely 

 localized, and the behavior often appears uncertain. The result- 

 ing behavior is consequently difficult to interpret. Notwithstand- 

 ing these objections, experiments in which very soluble substances 

 may be used are of value in order to learn in a general way what 

 effect the degree of solubility may have on ameba. 



Tyrosin. The product used bore Merck's guarantee of purity. 

 A mass of tyrosin thirty microns in diameter dissolves in water 

 in about ten minutes. A grain of tyrosin was placed in the path 

 of a granular ameba 6. The ameba turned to the right and 

 moved on, avoiding the tyrosin. A new grain of tyrosin was 

 then laid in the ameba's path and negative behavior again 

 followed 10. A third grain of tyrosin was then presented 13 

 and the ameba moved on past it with apparent indifference. 



