of the brain and results in sensation or perception, what grounds have we, on any physiological or scientific principle, for asserting that the change which follows is other than a higher manifestation of some nervous property?" (Structure and Development of the Brain, W. Collins, Sons & Co., 1879.)
If the above be a correct statement of the facts, and I believe it is, it follows that the brain is the medium or laboratory in which thoughtful reasoning and the higher mental phenomena are generated. As a corollary to this important deduction we expect the amount and quality of mental activities to be proportionate to the size of the cerebral organ. There is some latent truth in this idea, but in drawing definite conclusions of this nature from the actual bulk of brain substance there are some modifying influences to be considered. The actual bulk of an elephant's brain is about three times that of man. In making comparisons of this kind we must consider the relative size of the brain to the animal's body, and, above all, the quality of the brain cells, and no doubt many other factors. But for the present purpose we have only to deal with the brains of the anthropoid apes, and compare them with that of man. On this point Dr Thomson thus writes : —
}"The brains of the Anthropoid Apes, the Gorilla, the Chimpanzee, and Orang, all of which have now been well described by competent authors, are far inferior to that of man in the dimensions. Even in the Gorilla, which is most similar in stature to man, the brain does not attain more than a third of the weight of the average human brain, and in the Chimpanzee and Orang it does not even reach a fourth; and thus in these animals the proportion of the weight of the brain to that of the whole body may be as 1 to 100, or even lower, while the proportion in man is from 1 to 40 to 1 to 50." (Loc. cit., p. 31.)
So far, we have included man in our observations on animal life, but now we come to the parting of their ways.
The real problem which now confronts us is to account for the existence of man's large brain under the influence of existing cosmic forces. But before propounding any solution of the problem, it is advisable to bring into focus the discursive observations which I have laid before you, so that you may better realise where we are and what we are driving at.
Retrospect.
Glancing through the æons that have rolled past since life began on the globe, we have seen how myriads of generations
