system is more or less exercised, whether it be in connection with mere corporeal functions, or with mental processes, so do they take place to a greater or less extent. As relating to this subject it may be observed that the nervous substance is distinguished from all the other tissues (with the exception of the bones) by the very large proportion of phosphorus which enters into its composition, amounting to 1.5 parts in 100, and to as much as one-thirteenth of the solid matter which remains after the evaporation of the water; and that one result of over-exercise of the nervous system is the elimination of an unusual quantity of salts containing phosphorus by means of the secretion of the kidneys. This fact was first observed by Dr. Prout, who has given it as his opinion" that the phosphorus in organized beings is in some measure connected with nervous tissues and nervous action," and who in another place refers to "severe and protracted debilitating passions, and excessive fatigue, as the general exciting causes of" what he terms "the phosphatic diathesis.”* * On the Stomach and Renal Diseases, third edition. M 4. With regard to those more permanent changes in the brain to which Crites has referred as connected with the memory, and what is called the association of ideas, and I may add, with mental habits and dispositions as far as these are dependent on our physical organization, I have nothing to offer beyond what I have expressed already. There is, I apprehend, sufficient evidence that such changes do certainly take place, but as to their real nature we not only know nothing, but have no means of obtaining any actual knowledge. The improved microscope of the present day has enabled us to unravel to a considerable extent the minuter tissues of the animal body; but nevertheless, in pursuing an inquiry such as this, it affords us no assistance. There can be no doubt that there is as much in the animal structures beyond the reach of the microscope, as there is in the vast universe around us beyond the reach of the telescope; so that, whatever we might thus discover, we may sure that there is something further still. But let us suppose that it were otherwise, and be (assuming the molecular hypothesis to be true) that with more perfect organs of sense, or more perfect instruments, we could trace exactly the changes which take place in the arrangement or aggregation of the ultimate molecules of the brain, I do not see that we should be much advanced in knowledge. We shall be just as far from identifying physical and mental phenomena with each other as we are at present. The link between them would still be wanting, and it would be as idle to speculate on the nature of the relation between mind and matter, as on the proximate cause of gravitation, or of magnetic attraction and repulsion. 164 THE FIFTH DIALOGUE. Mental Faculties of Animals. Their Relation to the Structure of the Brain. Difficulty of the Inquiry, but some Knowledge of it not beyond our Reach.— Cerebral Organs connected with the Animal Appetites and Instincts.-Organs subservient to the Intellect.— Question as to the Uses of the Cerebral Convolutions. -The Posterior Lobes of the Cerebrum.-The Corpus Callosum.-The Development of the Mental Faculties, how far dependent on the Perfection of the Senses, and other external Circumstances.-The Nature and Office of Instinct.-Intelligence not peculiar to Man, nor Instinct to the lower Animals.-Human Instincts. -The Social Instinct and the Moral Sense. - Some Instincts as necessary to Animal Existence as the Circulation of the Blood, and other mere Animal Functions. Acquired Instincts transmitted from Parents to Offspring. These considered with reference to Moral and Political Science. - The Social Instinct viewed as correcting or modifying other Instincts, and as being made more efficient by the greater Development of the Intellect.-The Religious Instinct.-Primary Truths of Buffier and Reid. -- IT was one or two days after the conversation which has been just recorded, that we found ourselves in the afternoon on the side of a hill on which some sheep were scattered, watching the operations of the sheep-dog, who was collecting the flock previously to their being driven home for the night. This led to a conversation respecting the habits and faculties of animals; and Eubulus related the history of a dog who, having been taken in a carriage, and by a circuitous route, to a distant place, nevertheless, some time afterwards, found his way back to his former home, having, as it appeared, gone across a tract of country, with which he could have had no previous acquaintance. ERGATES. There are very many wellauthenticated instances of the same thing. It is even said that dogs carried across the sea have travelled back to their former place of abode, having established themselves on board ship for that purpose. Nor is this faculty peculiar to dogs. At least I have read an account of herds of cattle in New South Wales which, having been removed from their accustomed haunts to new pastures at a considerable distance, have nevertheless returned, not by the road which they had gone |