I prefer, while indulging in such speculations, to consider the various daily nomogeneously developed forms of protozoal or protistal jellies, sarcodes, and single-celled organisms, to have been as many roots from which the higher grades have ramified than that the origin of the whole organic creation is to be referred, as the Egyptian priests did that of the universe, to a single egg.
Amber or steel, when magnetised, seem to exercise "selection"; they do not attract all substances alike. A speck of protogenal jelly or sarcode, if alive, shows analogous relations to certain substances; but the soft yielding tissue allows the part next the attractive matter to move thereto, and then, by retraction, to draw such matter into the sarcodal mass, which overspreads, dissolves, and assimilates it. The term "living" in the one case is correlative with the term "magnetic" in the other. A man perceives ripe fruit; he stretches out his hand, plucks, masticates, swallows, and digests it.
The question then arises whether the difference between such series of actions in the man and the attractive and assimilative movement of the amæba be greater or less than the difference between these acts of the amæba and the attracting and retaining acts of the magnet.
The question, I think, may be put with some confidence as to the quality of the ultimate reply whether the amæbal phenomena are so much more different, or so essentially different, from the magnetic phenomena than they are from the mammalian phenomena, as to necessitate the invocation of a special miracle for their manifestation. It is analogically conceivable that the same cause which has endowed His world with power convertible into magnetic, electric, thermotic and other forms or modes of force, has also added the conditions of conversion into the vital force.
From protozoa or protista to plants and animals the graduation is closer than from magnetised iron to vitalised sarcode. From reflex acts of the nervous system animals rise to sentient and volitional ones. And with the ascent are associated brain-cells progressively increasing in size and complexity. Thought relates to the "brain" of man as does electricity to the nervous "battery" of the torpedo; both are forms of force and the results of action of their respective organs.
Each sensation affects a cerebral fibre, and, in so affecting it, gives it the faculty of repeating the action, wherein memory consists and sensation in a dream.
If the hypothesis of an abstract entity produces psychological phenomena by playing upon the brain as a musician upon his instrument be rejected, and these phenomena be held to be the result of cerebral actions, an objection is made that the latter view is "materialistic" and adverse to the notion of an independent, indivisible, "immaterial," mental principle or soul.
But in the endeavour to comprehend clearly and explain the functions of the combination of forces called "brain," the physiologist is hindered and troubled by the views of the nature of those cerebral forces which the needs of dogmatic theology have imposed on mankind. How long physiologists would have entertained the notion of a "life," or "vital principle," as a distinct entity if freed from this baneful influence may be questioned; but it can be truly affirmed that physiology has now established and does accept the truth of that statement of Locke—"the life, whether of a material or immaterial substance, is not the substance itself, but an affection of it."