THE FACTS OF SCIENCE 43 



they will call into some sort of activity a number of 

 physical impresses due to past sense-impressions allied, or, 

 to use a more suggestive word, attuned to the immediate 

 sense -impression. The immediate sense -impression is 

 conditioned by the physical impresses of the past, and the 

 general result is that complex of present and stored sense- 

 impressions which we have termed a " construct." 



Besides the sensory nerves which convey the messages 

 to the brain, there are other nerves which proceed from 

 the brain and control the muscles, termed motor nerves. 

 Through these motor nerves a message is sent to my hand 

 bidding it rub my bruised knee. This message may be 

 sent immediately or after my fingers have been dipped in 

 arnica. In the latter case a very coi;nplex process has 

 been gone through. I have realised that the sense- 

 impression corresponds to a bruised knee, that arnica is 

 good for a bruise, that a bottle of arnica is to be found in 

 a certain cupboard, and so forth. Clearly the sense- 

 impression has been conditioned by a number of past 

 impresses before the motor nerve of the arm is called into 

 play to rub the knee. The process is described as think- 

 ing, and as a variety of past experiences may come into 

 play, the ultimate message to the motor nerves appears to 

 us voluntary, and we call it an act of will, however much 

 it is really conditioned by the stored sense-impressions of 

 the past. On the other hand, when, without apparently 

 exciting any past sense-impressions, the message from the 

 sensory nerve no sooner reaches the brain than a command 

 is sent along the motor nerve for the hand to rub the 

 knee, I am said to act involuntarily, from instinct or habit. 

 The whole process may be so rapid, I may be so absorbed 

 in my work, that I never realised the message from the 

 sensory nerve at all. I do not even say to myself, " I 

 have knocked my knee and rubbed it." Only a spectator, 

 perhaps, has been conscious of the whole process of knee- 

 knocking and rubbing. Now this is in many respects an 

 important result. I can receive a sense-impression without 

 recognising it, or a sense-impression does not involve 

 consciousness. In this case there is no exciting of a group 



