302 Animal Life and Intelligence. 



CHAPTEE VIII. 



MENTAL PROCESSES IN MAN. 



I HAVE already drawn attention to the fact that the primary 

 end and object of the reception of the influences (stimuli) 

 of the external world, or environment, is to enable the 

 organism to answer or respond to these special modes of 

 influence, or stimuli. In other words, their purpose is to 

 set agoing certain activities. Now, in the unicellular 

 organism, where both the reception and the response are 

 effected by one and the" same cell, the activities are for 

 the most part simple, though even among these protozoa 

 there are some which show no little complexity of response. 

 Where, however, the organism is composed of a number of 

 cells, in which a differentiation of structure and a specializa- 

 tion of function have been effected, certain cells are set 

 apart as recipients, while other cells are set apart to 

 respond (respondents). There is thus the necessity of a 

 channel of communication between the two. Hence yet 

 other cells (transmitters), arranged end to end, form a line 

 of connection and communication between the group of 

 receiving cells and the group of responding cells, and con- 

 stitute what we term a nerve. That which is transmitted 

 may still be called a stimulus, each cell being stimulated 

 in turn by its neighbour. Thus a stimulus must be first 

 received and then transmitted. 



But little observation is required to convince us of the 

 fact that, in the higher creatures, a very simple stimulus 

 may give rise to a very complex response. A light pin- 

 prick will cause a vigorous leap in a healthy frog — a leap 

 that involves a most intricate, accurate, and complex 



