H. G. A. to H. M.

Thank you for your confirmations of so many points of interest.

It seems to me, that it is only by the study of our peculiarities and abnormal conditions that we shall gain light whereby to comprehend the ordinary and normal operations of our nature: and this knowledge, again, will enable us, at once, to perceive the cause and nature of every deviation from the true form. But knowledge has a progressive growth and natural course; and it is not in the power of the most suggestive mind to make any sudden leap. The discovery of a new instrument, or of a general law, alone enables us to make a stride in advance. The telescope, the power of which was not credited at first, gives us an extended range of observation; the microscope enables us to observe the more secret workings and minute structure of parts: by the electric telegraph we communicate in London with our friends in Edinburgh: by the stethoscope we detect the condition of internal portions of the body. The laws of light and gravitation extend over the universe, and explain whole classes of phenomena: the law of physiology, that each function has a special organ, and the extension of this law to the brain, explain the differences and variations in the condition of man, and his relations towards other animals.