Professor Ferrier has proved, by a multitude of minutely detailed experiments, that not only has each ganglion its function, but that each part of each ganglion is devoted to some special duty, thus completely shattering the theory that holds every mental operation to be an act of the whole brain. He establishes at least the grand basis of modern mental Science, the assumption that the brain is the material organ of the mind; that distinct parts of the brain are devoted to distinct mental operations; that not the whole brain, but only parts of it, are employed in any mental operation. The question is still open for observation and experiment to ascertain what are the parts of the brain so appropriated and what are the precise functions of each part.
Professor Ferrier has made considerable advances towards the determination of this question. His experiments have demonstrated what are the functions of the ganglia at the base of the brain, not being the seat of the Intelligence. His experiments were attended with more cruelty than I could excuse even for the important accessions they have brought to our knowledge. But they are not therefore the less valuable as contributions to Physiology and Psychology. I can but briefly describe the results of such of them as bear immediately upon the subject here treated of.
Let me, however, first confirm, by the authority of Professor Ferrier, the proposition I have ventured to advance as to the various functions of various parts of the brain.
“That the brain is the organ of the mind,” he says, “and that mental operations are possible only in and through the brain, is now so thoroughly well established and recognized that we may, without further question, start from this as an ultimate fact.” He proceeds:
The physiological activity of the brain is not, however, altogether co-extensive with its psychological functions. The brain as an organ of motion and sensation, or presentative consciousness, is a single organ composed of two halves; the brain as an organ of ideation, or re-presentative consciousness, is a dual organ, each hemisphere complete in itself. When one hemisphere is removed or destroyed by disease, motion and sensation are abolished unilaterally, but mental operations are still capable of being carried on in their completeness through the agency of the one hemisphere. The individual who is paralysed as to sensation and motion by disease of the opposite side of the brain (say the right), is not paralysed mentally, for he can still feel and will and think, and intelligently comprehend with the one hemisphere. If these functions are not carried on with the same vigour as before, they at least do not appear to suffer in respect of completeness.
As the object of this treatise is not anatomy but psychology, it will be unnecessary to describe minutely the entire of the brain structure. It will suffice for the present purpose to view the brain, above roughly sketched, as having three well marked divisions, each with definite and distinct functions.
The ganglia at the base of the brain govern the actions of the body. The ganglia in the centre of the brain are the recipients of the impressions made upon the senses and thus connect us with the external world. The two hemispheres at the summit of the brain are the organs of the Intelligence.
Professor Ferrier’s experiments were made with a view to ascertain whether the theory of Dr. Carpenter is true, that the whole brain works in each mental action, or if the phrenological doctrine be the true one, that the several parts of the brain have several and distinct functions. Dr. Carpenter had prematurely boasted that he had killed Phrenology. The boast would have been justified if his assertion (for it was merely a dogma, not a proved fact) had been found to be true. But Professor Ferrier’s experiments have decisively disproved the boast of Dr. Carpenter and killed his theory of mental unity.