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A TEXTBOOK OF PHYSIOLOGY 



is shown, and his left hand when a green one is shown, the time is con- 

 siderably longer than if he has to make a simple motor response with 

 one hand to any kind of disc. Still more complex is the process 

 when the subject has to speak different words in response to different 

 forms of stimulation. 



Mind and Consciousness. Extero-, proprio-, and entero-ceptive im- 

 pulses stream into the central nervous system from the time of its 

 embryonic development until death, ceaselessly modify the pattern 

 of its structure, lay down the pathways of reflex actions, and establish 

 habits. A very large proportion of these impulses, and particularly 

 the proprio- and entero-ceptive, never enter into consciousness, and 

 yet occasion actions which are perfectly adapted to the end in view. 



PIG. 447. DIAGRAM OF THE APPARATUS FOR THE DETERMINATION OF REACTION 

 TIME. (W. G. Smith.) 



The electro-magnetic tuning-fork T, with 100 vibrations per second, is connected 

 with two Daniell cells and with the chronograph O. By means of either of the 

 two Du Bois keys, K l and K 2 , the chronograph can be short-circuited. The key 

 K l is closed and K. 2 is open; the tuning-fork is set vibrating, but does not affect 

 the chronograph. The subject, whose reaction time is to be determined, is told 

 to listen for the sound of the opening of the key K v and to close the key A'.> 

 directly he hears the sound. When the key K 1 is opened the chronograph" 

 vibrates in unison with the tuning-fork and the vibrations are recorded upon a 

 revolving drum; the closure of the key K 2 by the subject of the experiment 

 brings the chronograph to rest. The number of vibrations recorded upon the 

 drum gives the reaction time for sound in T^ths of a second. 



For example, the character cf the saliva secreted is adapted according 

 as sand or bread is put into the mouth. In the one case a watery 

 saliva is secreted, in the other a saliva containing the ferment ptyalin. 

 It might be argued that the salivary centre felt, judged, and willed 

 an appropriate action, and yet none of these processes enter into 

 consciousness. We each have from moment to moment of our waking 

 life a general consciousness of well-being or the reverse, maintained by 

 proprio- and entero-ceptive impulses arising in the organs and tissues 

 of the body, coupled with a tone of feeling evoked by extero-ceptive 

 sensations. These arouse in us from time to time emotions of in- 

 difference, pleasure, pain, affection, hate, sex, etc. The more powerful 

 extero-ceptive sensations not only enter into consciousness, but sc- 

 atter the pattern of the brain structure as to store memories in what 



