65. Living Bodies differ from Mineral Bodies in their Essential Composition, in the manner of their Growth, and in the fact that they are reproduced by Germs.
Thus there is a very broad distinction between mineral matter and living matter. The elements of living matter are identical with those of mineral bodies; and the fundamental laws of matter and motion apply as much to living matter as to mineral matter; but every living body is, as it were, a complicated piece of mechanism which “goes,” or lives, only under certain conditions. The germ contained in the fowl’s egg requires nothing but a supply of warmth, within certain narrow limits of temperature, to build the molecules of the egg into the body of the chick. And the process of development of the egg, like that of the seed, is neither more nor less mysterious than that, in virtue of which, the molecules of water, when it is cooled down to the freezing-point, build themselves up into regular crystals.
The further study of living bodies leads to the province of Biology, of which there are two great divisions—Botany, which deals with plants, and Zoology, which treats of animals.
Each of these divisions has its subdivisions—such as Morphology, which treats of the form, structure, and development of living beings, and Physiology, which explains their actions or functions, besides others.
III. IMMATERIAL OBJECTS.
66. Mental Phenomena.
Material objects are all either not living, that is to say, mineral bodies, or they are living bodies. Everything which occupies space, offers resistance, has weight and transfers motion, belongs to one or other of these two great provinces of nature. The sciences of Astronomy, Mineralogy, Physics, and Chemistry deal with the former, while Biology, with its two divisions of Zoology and Botany, treats of the latter. But natural knowledge is not exhausted by this catalogue of its topics. In the very first paragraph of this Primer, in fact, we had occasion to draw a distinction between Things, or material objects, and Sensations; and a moment’s reflection is sufficient to convince you that sensations are not material objects. A smell takes up no space and has no weight; and to speak of a pound or of a cubic foot of sound, or of brightness, is, on the face of the matter, an absurdity. Pleasure is said metaphorically to be fugitive, but you cannot imagine a pleasure as a thing in motion.
What we call our Emotions are in like manner devoid of all the characters of material bodies. Love and hatred, for example, cannot for a moment be conceived to have shape, or weight, or momentum. And when, in reasoning, we think, our Thoughts have the same lack of the qualities of material things.
Sensations, emotions, and thoughts, thus constitute a peculiar group of natural phenomena, which are termed mental.