Theories of Development 239 



cells into perceptions and associated ideas. Thus it is 

 found that sensation gives rise to perceptions; these 

 in turn blend in consciousness into simple ideas of 

 particular things. Simple or particular ideas blend, 

 by association, into more complex or general ideas, which 

 may be abstracted from the original sensations after 

 the brain centers have acquired that power of nervous 

 discharge which seems to come through repetition of 

 external impressions. Hence general ideas, instead 

 of being inborn or innate, are supposed to originate 

 from the simpler particular ideas. 



This entire process may take place very rapidly 

 during the first years or even weeks of life, so that the 

 process is largely an unconscious one at first. Sub- 

 conscious mental states are thought to exist; the 

 organic life, it is believed, ministers to the whole 

 conscious life of the mind. The lower ganglia of the 

 brain may be concerned in purely reflex or automatic 

 acts without being accompanied by consciousness; 

 or, on other occasions, they may serve as relays of 

 nerve energy, by which the cortical cells may be aroused 

 to activity. Thus the higher proceeds from the lower, 

 just as the simple ganglia of the jellyfish may be a 

 step in the evolution of the nervous system of higher 

 animals. The complex brain arises from the union 

 of many simple nerve-cells or neurons, just as the 

 general idea is supposed to arise from the union of 

 simple ones, the original elements of those simple 

 ideas being sensations. 



Now, the nervous system and sense-organs are parts 

 of the body, subject to the same laws of health and 

 disease as are other bodily organs. The nervous 

 system, with which the mind is associated, is par- 

 ticularly susceptible to changes of all kinds; and is, 

 therefore, well adapted to receive impressions of all 

 those changes, both in the body and in the external 

 worJd, which occasion mental states. Variations in 



