_Method of Degeneration._--This consists in observing the progress of natural or artificially produced disease or damage to the tissues, mainly the nervous tissues, with a view to discovering the directions of pathways and the locations of connected functions.

The degeneration or decay following disease or injury follows the path of normal physiological action, and so discloses it to the observer.

This method is of importance to psychology as affording a means of locating and following up the course of a brain injury which accompanies this or that mental disease or defect.
_Results_--_Localization of Brain Functions._--The more detailed results of this sort of study, when considered on the side of the nervous organism, may be thrown together under the general head of Localization.

The greatest result of all is just the discovery that there is such a thing as localization in the nervous system of the different mental functions of sensation and movement.

We find particular parts of the nervous organism contributing each its share, in a more or less independent way, to the whole flow of the mental life; and in cases of injury or removal of this part or that, there is a corresponding impairment of the mind.
First of all, it is found that the nervous system has a certain up-and-down arrangement from the segments of the spinal cord up to the gray matter of the rind or "cortex" of the large masses or hemispheres in the skull, to which the word brain is popularly applied.