14 METHODS OF MICROSCOPICAL RESEARCH. 



as an aid to vision, we must, at the outset, recognise 

 the importance of a study of the human eye. 



It may be the seat of many imperfections result- 

 ing from misuse, old age, or disease, which are apt 

 to modify the conclusions we may draw from our 

 observations, unless we are careful to study well 

 into what lines such imperfections may lead us. 



Nature has given us in this organ a means 

 whereby all objects may be compared with each 

 other, more especially as to size, colour, and general 

 characters, and it must astonish the student, who 

 thinks deeply, to find that so little is known definitely 

 as to how we are able to appreciate magnitudes, 

 colours, and forms. It is easy to say that the lenses 

 of the eye focus a picture of the object upon the 

 retina, and the irritations are carried by the optic 

 nerve to the brain, but do we practically realise 

 what this means ? 



Then, again, unless more of our senses than one 

 are brought to bear upon a matter under considera- 

 tion, we can scarcely form a true opinion upon our 

 subject. 



Take something which greets our vision for the 

 first time. We know not what it is ; we can see 

 it, it is true, but we have to bring in the aid of 

 other senses before we can arrive at a correct 

 judgment; and even then, our judgment being the 

 result of comparison, and also of experimental 

 contact of substances with our senses so to speak 

 opinions which are formed must, to a certain 

 extent, be modified by the amount of other 

 experience to which our nerve centres have been 

 previously subjected. 



Take two experts; give to each one a sphere 



