In the foregoing pages we have had intimations of some of the important questions which arise about the connection of mind with body. The avenues of the senses are the normal approaches to the mind through the body; and, taking advantage of this, experiments are made upon the senses. This gives rise to Experimental Psychology, to which the chapter after this is devoted. Besides this, however, we find the general fact that a normal body must in all cases be present with a normal mind, and this makes it possible to arrange so to manipulate the body that changes may be produced in the mind in other ways than through the regular channels of sense. For example, we influence the mind when we drink too much tea or coffee, not to mention the greater changes of the same kind which are produced in the mind of the drinker of too much alcohol or other poisonous substances. 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. 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.