All the methodical means of procedure by which the psychologist produces effects of this kind by changing the condition or functions of the body within itself belong to Physiological Psychology.

So he modifies the respiration, changes the heart beat, stimulates or slows the circulation of the blood, paralyzes the muscles, etc.

The ways of procedure may be classified under a few heads, each called a method.
1.

_Method of Extirpation._--This means simply the cutting away of a part of the body, so that any effect which the loss of the part makes upon the mind may be noted.

It is used especially upon the brain.
Pieces of the brain, great or small--indeed, practically the whole brain mass--may be removed in many animals without destroying life.
Either of the cerebral hemispheres entire, together with large portions of the other, may be taken from the human brain without much effect upon the vital processes, considered as a whole; the actual results being the loss of certain mental functions, such as sight, hearing, power of movement of particular limbs, etc., according to the location of the part which is removed.