CONSCIOUSNESS. 179 



the higher associational activity of the brain, the 

 formation of judgments and their connection into 

 chains of reasoning, thought, and consciousness in 

 the narrower sense, are developed in them after the 

 same fashion as in man : they differ only in degree, 

 not in kind. Moreover, we learn from comparative 

 anatomy and histology that the intricate structure 

 of the brain (both in general and in detail) is sub- 

 stantially the same in the mammals as it is in man. 

 The same lesson is enforced by comparative ontogeny 

 with regard to the origin of these psychic organs. 

 Comparative physiology teaches us that the various 

 states of consciousness are just the same in these 

 highest placentals as in man ; and we learn by ex- 

 periment that there is the same reaction to external 

 stimuli. The higher animals can be narcotised by 

 alcohol, chloroform, ether, etc., and may be hypnotised 

 by the usual methods, just as in the case of man. 



It is, however, impossible to determine mathemati- 

 cally at what stage of animal life consciousness is to 

 be first recognised as such. Some zoologists draw the 

 line very high in the scale, others very low. Darwin, 

 who most accurately distinguishes the various stages 

 of consciousness, intelligence, and emotion in the 

 higher animals, and explains them by progressive 

 evolution, points out how difficult, or even impossible, 

 it is to determine the first beginning of this supreme 

 psychic faculty in the lower animals. Personally, 

 out of the many contradictory theories, I take that 

 to be most probable which holds the centralisation of 

 the nervous system to be a condition of consciousness ; 

 and that is wanting in the lower classes of animals. 

 The presence of a central nervous organ, of highly- 

 developed sense-organs, and an elaborate association 



