2. _Method of Artificial Stimulation._--As the term indicates, this method proceeds by finding some sort of agent by which the physiological processes may be started artificially; that is, without the usual normal starting of these processes. For example, the physician who stimulates the heart by giving digitalis pursues this method. For psychological purposes this method has also been fruitful in studying the brain, and electricity is the agent customarily used. The brain is laid bare by removing part of the skull of the animal, and the two electrodes of a battery are placed upon a particular point of the brain whose function it is wished to determine. The current passes out along the nerves which are normally set in action from this particular region, and movements of the muscles follow in certain definite parts and directions. This is an indication of the normal function of the part of the brain which is stimulated. Besides this method of procedure a new one, also by brain stimulation, has recently been employed. It consists in stimulating a spot of the brain as before, but instead of observing the character of the movement which follows, the observer places galvanometers in connection with various members of the body and observes in which of the galvanometers the current comes out of the animal's body (the galvanometer being a very delicate instrument for indicating the presence of an electric current). In this way it is determined along what pathways and to what organs the ordinary vital stimulation passes from the brain, provided it be granted that the electric current takes the same course. 3. _Method of Intoxication, called the "Toxic Method._"--The remarks above may suffice for a description of this method. The results of the administration of toxic or poisonous agents upon the mind are so general and serious in their character, as readers of De Quincy know, that very little precise knowledge has been acquired by their use. 4. _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.