402 MENTAL FUNCTION 



system. Every muscle-fiber is continually in a state of at least tonic 

 contraction, and every viscus of the thorax and the abdomen knows only 

 a relative sort of rest. Thus changeful is the "physical basis" of the 

 mental process, but how it is not here our business to inquire. 



Another characteristic of the stream of consciousness is that while 

 thus made up of "parts," yet these more or less merge into each other and 

 form a unity. In technical terms consciousness is a continuum. In a 

 similar way an hour is a continuous series of minutes and seconds, and a 

 river, although made up of drops or gallons, is yet a continuum of water 

 flowing as a stream. A little later we shall see something of the nature 

 or at least of the origin of these quasi parts which pass into the continuum 

 of consciousness. As long as life endures the mental process stops no 

 more than does the metabolism of the heart or the chemical activities 

 of the brain, although its intensity and its breadth and depth vary greatly 

 from minute to minute, and become much lessened especially during 

 sleep. Heraclitus of old used to say that a man could bathe in a river 

 only once, for the river in which he bathed the second time was no 

 longer the same. Closer analysis of the stream of consciousness suggests 

 that a person cannot bathe in the same river even once, for even while 

 he is bathing the stream is changing around him. It is the chief purpose 

 of descriptive psychology to make plain the numerous shifting but 

 recurring qualities of this conscious river. 



The third characteristic of consciousness of which the introspecting 

 individual is always aware is that its states are invariably referred to a 

 unifying personality. Continually there is self-reference, a certainty 

 of a personal identity. It is only in abnormal conditions whose physical 

 "basis" is unknown that the mental process related to any organism 

 loses its identity and splits into two or more personalities. Here is one 

 of the paradoxes which continually remind us of the intricacy of things. 

 Notwithstanding this, however, we may be sure that the mental process 

 of the normal man or woman is always unified by an underlying sense 

 of individuality. The feelings we experience and the thoughts we 

 think get their value for us only as they come directly or indirectly into 

 relation with this personal subjectivity which behind, beneath, and all 

 through this tide of changing experience persists unchanged. By this 

 alone consciousness is made real, kept in range of flesh and blood, made 

 something more than the evanescent shadow of a dream. 



This individuality not only experiences the stream of consciousness, but 

 directs it to a greater or a less degree. We cannot only control and 

 force our thoughts into any desired direction under normal conditions, 

 but our feelings are more or less subconsciously determined by the 

 nature of our personalities as developed by our experience. What one 

 sees and takes an interest in is determined by no means wholly by the 

 nature of what his eyes actually see. What we perceive is often to a large 

 extent decided by what is already present in our minds. A lumberman, 

 for example, sees in a forest the size and straightness and number and 

 proportions of the trees. An artist sees in the same trees only their 



