460 STUDIES IN ADVANCED PHYSIOLOGY. 



an every-day experience that one will go along a path step- 

 ping over all obstacles, walking around obstructions, getting 

 out of the way of passers-by or vehicles, stepping carefully 

 sometimes over pools of water, even ascending steps, and 

 yet do all of this without the slightest apparent intervention 

 of consciousness. During all of this time a person may be 

 deeply absorbed in some train of thought, and if he were 

 questioned at the end of his journey about any of the de- 

 tails of the way would be utterly unable to recall even a 

 few. It is of course also evident that nearly all of the 

 motions of the body are guided by the sensations of sight. 

 True an individual may walk or run with his eyes shut and 

 depend upon other sensations, but that is only possible 

 where the individual knows the road to begin with, or is 

 supremely indifferent to accidents. Ordinarily speaking, 

 the visual impressions which never reach consciousness are 

 the guides which determine the motions of the body. These 

 complicated reflexes have their seat in the optic thalami or 

 mid-brain, and for the final execution of some of the habitual 

 movements of the body the cerebellum also comes into play. 

 It needs no special comment to point out what a saving of 

 energy it is to the higher centers of the brain to be relieved 

 from the interpretation of the crowd of sensations pouring 

 in through eye (or ear) and their proper reflection into cor- 

 respondingly purposeful motor impulses. 



It will be pointed out later that the place where visual 

 sensations come into the field of consciousness lies in the 

 occipital lobes of the brain. Here seems to be the curtain 

 of the mind against which the images are projected for 

 direct and conscious scrutiny. But a small proportion, 

 however, of the visual sensations reach this high conscious 

 center. Most of them never get beyond the sub-conscious 

 and reflex centers of optic thalami and mid-brain. An 

 animal whose occipital lobes are removed, and which is 

 therefore consciously blind, is still able to avoid obstacles 

 in its way and prevent itself from stumbling over obstruc- 

 tions by going around them, on account of the fact that the 



