A man receives only what he is ready to receive, whether physically or intellectually or morally, as animals conceive at certain seasons their kind only. We hear and apprehend only what we already half know. If there is something which does not concern me, which is out of my line, which by experience or by genius my attention is not drawn to, however novel and remarkable it may be, if it is spoken, we hear it not, if it is written, we read it not, or if we read it, it does not detain us. Every man thus tracks himself through life, in all his hearing and reading and observation and traveling. His observations make a chain. The phenomenon or fact that cannot in any wise be linked with the rest which he has observed, he does not observe. By and by we may be ready to receive what we cannot receive now. I find, for example, in Aristotle some thing about the spawning, etc., of the pout and perch, because I know something about it already and have my attention aroused; but I do not discover till very late that he has made other equally important observations on the spawning of other fishes, because I am not interested in those fishes.