4IO HARRY THOMAS FOLGER. 



mechanical shock, and that the period of quiescence amounted to 

 4.5 seconds. Twenty seconds for recovery resulted in 3 reac- 

 tions out of 3 trials, with an average period of quiescence of 5.8 

 seconds, 25 seconds for recovery resulted in 4 reactions out of 4 

 trials, with an average period of quiescence of 9.1 seconds, and 

 35 seconds for recovery resulted in 2 reactions out of 2 trials, 

 with an average period of quiescence of 20 seconds. 



Thus it appears that not only does sudden illumination affect the 

 response of an amceba to mechanical shock, but that it has pre- 

 cisely the same effect as another mechanical shock. 



DISCUSSION. 



A similarity of response to various kinds of stimuli has been 

 noted in other organisms. Ewart ('03) has collected considerable 

 data concerning protoplasmic streaming in plant cells, especially 

 in the cells of Chara and Nitclla. He and others have found that 

 the cells react in a very characteristic way to various stimulating 

 agents, the response consisting, just as in Amoeba, of a temporary 

 cessation of movement. The best quantitative results were ob- 

 tained by means of a mechanical shock, brought about by drop- 

 ping a weight on the coverslip beneath which the streaming cells 

 had been placed. By using weights of various sizes a gradation 

 in the magnitude of the shock was possible. Ewart discovered 

 that streaming did not stop immediately on application of the 

 stimulus, but after the intervention of a reaction-time, which was 

 longer after a light shock than after one of greater magnitude and 

 which in the event of a sub-minimal stimulus might amount to 7 

 or 8 seconds. He found, furthermore, that the time during 

 which movement remained suspended likewise depended on the 

 magnitude of the shock, streaming recommencing much sooner 

 after a slight shock than after a heavy one. Various other stimu- 

 lating agents, including light, heat, electricity, and change in con- 

 centration of the surrounding medium, gave very similar results, 

 although in no instance was so accurate a quantitative measure- 

 ment obtained as with mechanical shock. Ewart also noted that 

 the application of one kind of stimulus may tend to inhibit the 

 response to another kind. 



