298 SPECIAL PHYSIOLOGY. 



which constitute the sensorium, excite the consciousness and produce 

 sensation. Sensation is the simplest psychical process, and sensations 

 are, so to speak, the sources of all further mental activity. For the 

 occurrence of temporary sensations, excited from without or from 

 within, mere consciousness alone is sufficient ; but when such sensa- 

 tions are to be rendered useful, as the subjects of succeeding mental 

 operations, an internal active process is essential, viz., that of atten- 

 tion. Without this condition, impressions may sometimes be pro- 

 duced, and yet their effects on the consciousness may remain com- 

 pletely unnoticed. The sensory impressions, when realized through 

 the attention, probably by aid of some simultaneous changes in the 

 cerebral hemispheres, are then, by the act of perception, a far higher 

 mental process, referred to their proper external causes, and thus suc- 

 cessions of so-called ideas are formed. The formation of such ideas 

 has been named ideation. Now, an idea may be transitory ; but, on 

 the other hand, it may also leave behind, probably in connection with 

 some deeper changes in the nervous substance, a more permanent im- 

 pression, and, by some occasional cause, by association, or, after prac- 

 tice, by the force of the will, it may again be called into existence, 

 and this process is aptly named recollection, and the faculty by which 

 it is accomplished, memory. These ideas constitute the materials of 

 further thought, i. e., of association, comparison, and combination; and 

 hence arise, amongst other notions, those of the distinction between 

 the body or corporeal frame and the outer world, or what are some- 

 times erroneously designated the subject and the object; also such 

 notions as repetition, mass, and the sequence of events. 



The higher animals are also capable of forming such ideas, and can 

 compare and combine them in the act of thinking, so as to attain cer- 

 tain notions, and to acquire a given amount of knowledge and experi- 

 ence. But the sphere of this knowledge is limited, the ideas on which 

 it is based are simple, and the notions formed are what are termed 

 concrete; whilst the actions which follow, still refer merely to the 

 conditions of their individual life, such as the obtaining of food, the 

 avoidance of danger, pain, or injury, and the satisfaction of impulses 

 which tend towards the maintenance of the species. By means of 

 education and special training, a wider range of ideas and notions 

 still, however, of the concrete form may, with time and labor, be 

 imparted to, or aroused in, certain animals ; but these are all extin- 

 guished with the individual, and are lost for the species. At the same 

 time, certain special instincts, capable of cultivation, which are in no 

 way due to processes of reason, and are certainly not the results of 

 teaching, but rather of primary impulses, originating in the organiza- 

 tion and nature of the individual animals, may be trained, and strength- 

 ened, and so transmitted, in the form of habits to the young, as is 

 seen in the case of certain breeds of dogs. 



In the human mind, however, besides the perception of simple con- 

 crete ideas, and the formation of concrete notions, abstract ideas arise 

 by the further mental process called abstraction, and sometimes con- 

 ception. Not merely is the outer world perceived by man, and recog- 

 nized as an existence external to himself, consisting of objects and 



