22 THE EYE 



belong to the domain of the free, and for that very reason, 

 fallible activity of the mind. Great circumspection, a very 

 comprehensive training, must the mind possess, before it 

 can free itself from all its own misconceptions and learn 

 wholly to command itself. Sight, in the common sense 

 of the word, appears to us so easy, yet is it a difficult 

 art. Only by degrees do we learn what messages 'of the 

 senses we may trust, and how to form our conceptions 

 from them. Men of science may themselves err here err 

 often, and the oftener, the less they comprehend where they 

 have to seek for the source of error. 



But still more striking than the relations just unfolded, 

 is the fact, that the master, that is the soul, receives 

 messages from his servants, the nerves, and delivers orders 

 to them without being conscious at the moment of their 

 presence. Not at first, but after his knowledge has pro- 

 gressed far forward, does man discover that nerves exist 

 and have their appointed functions. He sees and knows 

 not of his optic nerve, a burnt hand pains him but he is 

 all unconscious of the fibres that convey the impression ; he 

 moves the tongue playing with fluent rapidity, but is 

 ignorant of the course of its appointed nerves. In a word, 

 we never experience the condition of a nerve, but form a 

 conception of an external object immediately the nerve is 

 excited, and it required scientific intelligence to recognize 

 this object as the cause of the excitement of a nerve. 



However, to retain the comparison we have chosen, if 

 the relation of the master to his servants is one wholly 

 peculiar, the servants are no less of a quite especial kind. 

 No one of them knows anything of another, is at all aware 

 of his existence and activity, or shares it with him. Nay, 

 what is still more important, no one of them, that is no 

 nervous fibril, can carry more than one single, simple 



