Many of the facts given below under the heading of Localization were discovered in this way, the guiding principle being that if the loss of a function follows the removal of a certain piece of the brain, then that portion of the brain is directly concerned in the healthy performance of that function.
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.