AMEBA 57 



trated by the response of a definite point on the body of 

 Ameba to a strong mechanical stimulus. This may be compared 

 with what happens when a mass of inorganic material is acted 

 upon by a force; here a reaction is produced directly at the 

 point of contact. In orienting itself in the direction of the light 

 rays, Ameba shows a response to a continuous stimulus which 

 affects the entire body (Fig. 22); if the source of illumination 

 is changed, the animal changes its orientation. The cause of 

 the reaction, as in the above instance, seems to be in most 

 cases a change in the environment. The response is always pro- 

 duced by a stimulation directly preceding it, but the animal soon 

 becomes acclimated to the new environment, and its activities 

 become normal. This is shown when it is transferred from one 

 culture to another (chemotropism) or when white light is thrown 

 upon it (phototropism). 



The reactions of Ameba to stimuli are of undoubted value to 

 the individual and to the preservation of the race, for in every 

 instance the negative reaction is produced by injurious agents 

 such as strong chemicals, heat, and mechanical impacts, while 

 positive reactions are produced by beneficial agents. The re- 

 sponses, therefore, in the former cases carry the animal out of 

 danger, in the latter, toward a safer haven. 



Ameba is of fundamental interest to animal psychologists, 

 since it represents the " animal mind " in its most primitive 

 form. The behavior of Ameba in the absence of external stimuli, 

 for example when it is suspended freely in the water, shows that 

 some of its activities are initiated by internal causes. Whether 

 or not the animal is in any degree conscious is a question still 

 unanswered. If Ameba has recognizable sensations, they must 

 be infinitely less in both quality and quantity than in higher 

 organisms. Furthermore, it is unable to learn from the few kinds 

 of experiences it does pass through, and is therefore lacking in 

 memory images. One case in which an Ameba attempted to 

 capture another is recorded by Jennings, and seems to point to 

 something higher than mere physical and chemical attractions. 



