July 4, 1902.] 



SCIENCE. 



In one sense this may be called a defini- 

 tion of consciousness, but inasmuch as it 

 does not tell what consciousness is, but 

 only what it does, we have not a true defi- 

 nition, but a description of a function. 

 The description itself calls for a brief ex- 

 planation. We receive constantly numer- 

 ous sensations, and in response to these 

 we do many things. These doings are, 

 comprehensively speaking, our reactions to 

 our sensations. When the response to a 

 stimulus is obviously direct and immediate 

 we call the response a reflex action, but 

 a very large share of our actions are not 

 reflex but are determined in a far more 

 complicated manner by the intervention of 

 consciousness, which may do one of two 

 things: (1) Stop a reaction, as, for ex- 

 ample, when something occurs, calling, as 

 it were, for our attention and we do not 

 give our attention to it. This we call con- 

 scious inhibition. It plays a great role 

 in our lives ; but it does not mean neces- 

 sarily that inhibited impressions may not 

 survive in memory and at a later time 

 determine the action taken; in such cases 

 the potential reaction is stored up. (2) 

 Consciousness may evoke a reaction from 

 a remembered sensation and combine it 

 with sensations received at other times. In 

 other words, consciousness has a selective 

 power, manifest both in choosing from 

 sensations received at the same time and 

 in combining sensations received at differ- 

 ent times. It can make synchronous im- 

 pressions dyschronous in their effects, and 

 dyschronous impressions synchronous. But 

 this somewhat formidable sentence merely 

 paraphrases our original description: The 

 function of consciousness is to dislocate 

 in time the reactions from sensations. 



This disarrangement and constant rear- 

 rangement of the sensations, or impressions 

 from sensations, which we gather, so that 

 their connections in time are altered seems 

 to me the most fundamental and essential 



characteristic of consciousness which we 

 know. It is not improbable that hereafter 

 it will become possible to give a better char- 

 acterization of consciousness. In that case 

 the opinion just given may become unsatis- 

 factory, and have to yield to one based on 

 greater knowledge. The characteristic we 

 are considering is certainly important, and 

 so far as the available evidence goes it 

 belongs exclusively to consciousness. With- 

 out it life would have no interest, for there 

 would be no possibility of experience, no 

 possibility of education. 



Now the more we have learned about 

 animals, the better have we appreciated the 

 fact that in them only such structures and 

 functions are preserved as are useful, or 

 have a teleological value. Formerly a good 

 many organs were called rudimentary or 

 vestigial and supposed to be useless sur- 

 vivals because they had no known func- 

 tion. But in many cases the functions have 

 since been discovered. Such, for example, 

 were the pineal gland, the pituitary body, 

 the suprarenal capsules and the Wolffian 

 body of man, all of which are now recog- 

 nized to be functionally important struc- 

 tures. Useless structures are so rare that 

 one questions whether any exist at all, ex- 

 cept on an almost insignificant scale. It 

 has accordingly become well-nigh impos- 

 sible for us to imagine consciousness to 

 have been evolved, as it has been, unless it 

 had been bionomically useful. Let us there- 

 fore next consider the value of conscious- 

 ness from the standpoint of bionomics.* 



We must begin with a consideration of 

 the nature of sensations and the object of 

 the reactions which they cause. In the 

 simpler forms of nervous action a force, 

 usually but not necessarily external to the 

 organism, acts as a stimulus which causes 



* A convenient term, recently gaining favor, for 

 what might otherwise be called the economics of 

 tlie living organism. Bionomics seems preferable 

 to ecology, which some writers are adopting from 

 the German. 



