NERVOl'S SYSTEM AND SENSE ORGANS 



II. Protozoa 



In Amoeba, there seems to be no portion of the surface more 

 sensitive than others. The exoplasm is a general sensory organ. 



Experiments by Hyman '17, with toxic substance show that a 

 local region of increased susceptibility exists along the axes of each 

 pseudopodium from it^ distal to its proximal end, the distal end 

 being more suscejitible. The youngest and most vigorous forms 

 are most susceptible. 



According to several investigators, the exoplasm of Amoeba is 

 like a tough skin and this in part at least acts as a sensory area. 

 The more fluid endoplasm may become quite rigid under stimulation. 



The changes in Amoeba which are the causes of amoeboid 

 movement and behavior originate within the Amoeba and external 

 stimuli do not act directly to produce those physical alterations 

 which result in movement, but they act through the jn-otoplasm of 

 the Amoeba. The reactions of Amoeba are similar to the reflexes 

 of more complex forms involving reception of stimuli, and the con- 

 duction of internal changes leading to response, but sensation, con- 

 duction and movement are not differentiated. 



If one side of an Amoeba touches .some object it may move 

 away from the .source of stimulus. Jennings has found that when 

 touched the animal does not usually move directly awav from the 

 side stimulated, but merely in some other direction. If the anterior 

 edge is touched this part stops and contracts while the current 

 turns to one side at this point, so that the animal moves at an angle 

 with its former direction. If the advancing edge of an Amoeba is 

 touched it withdraws and a new pseudopodium is sent out else- 

 where. Sometimes Amoebae react positively to .solid bodies, they 

 may also under various sorts of .stimuli thrust out many pseu- 

 dopodia at once or draw all into a compact mass. Amoeba reacts 

 not only to mechanical but also to chemical, temperature, light and 

 electrical stimuli. The direction of movement in negative reac- 

 tions is not determined entirely by the position of the stimulating 

 agent. Other .stimuli may have already altered the character of the 

 protopla.sm, for exanii)le the moving Amoeba is temporarily dif- 

 ferentiated, having two ends different and the sides differing from 

 the ends. The.se and i)erhaps other internal factors have a large 

 part in the determination of movement. 



It is impo.ssible to explain how Amoeba alters its own metabolic 

 process. If Amoeba is capable of self stimulation then this might 

 suggest that living sub.stance has a psychic quality which is pos- 

 sessed by all protoplasm. If this is not accepted for sim|)ler organ- 

 isms it would be hard to accept it for the cells of the cerebral cortex 

 of man and all would be referred to present or past conditions of 

 external or internal environment. 



There is no clear evidence that Amoeba has memorv. The 



