RESPONSES BY AMCEBA. 407 



struck one end of the slide containing the amoeba. Light was 

 procured from a i,ooo-watt, H2-volt, cylindrical Mazda stere- 

 opticon lamp, and flashed upon the amoeba by means of the plane 

 mirror of the microscope, set at an angle of 45 degrees. An in- 

 tensity of about 16,000 meter candles was employed. To observe 

 the organism when it was not illuminated by the strong light use 

 was made of a Spencer miniature substage lamp. 



The amoeba to be experimented on was placed in a drop of 

 water on a glass slide, within a ring of vaseline, and beneath a 

 thin coverslip which was supported on one side by a small glass 

 rod. The microscope was so arranged that when the amoeba was 

 in position under the lens, light could be flashed upon it or a 

 mechanical shock applied at the will of the investigator, and the 

 effect of one stimulus upon the other noted. 



EXPERIMENTAL RESULTS. 

 Table I. illustrates the effect of mechanical shock upon the re- 



TABLE I. 



ILLUSTRATING THE EFFECT OF MECHANICAL SHOCK UPON THE RESPONSE TO 



SUDDEN ILLUMINATION. 



In each trial the amoeba was exposed to strong illumination, and in every 

 other one it was subjected to a mechanical shock before being illuminated. 

 Three minutes were allowed between tests. 



Number of No 

 Trials. Reactions. 



Sudden illumination alone 5 



Sudden illumination following shortly after a mechanical 

 shock 6 4 



sponse to light. The experiment from which the data in this 

 table were derived consisted of a number of tests, in each of which 

 the amoeba was exposed to strong illumination, and in every other 

 one of which it was subjected to a mechanical shock before being 

 illuminated. This shock was of sufficient magnitude to cause a 

 cessation of movement, and the animal was exposed to light im- 

 mediately on the resumption of flow. An interval of three min- 

 utes between tests permitted a recovery from the effects of previ- 

 ous stimulation. As shown in the table the amoeba failed to re- 

 spond to light 4 times out of 6 trials when a mechanical shock 



