There seems nothing more wonderful in the ether of contraction producing the shortening of a fibre, than in the ether of attraction causing two bodies to approach each other. The former indeed seems in some measure to resemble the latter, as it probably occasions the minute particles of the fibre to approach into absolute or adhesive contact, by withdrawing from them their repulsive atmospheres; whereas the latter seems only to cause particles of matter to approach into what is popularly called contact, like the particles of fluids; but which are only in the vicinity of each other, and still retain their repulsive atmospheres, as may be seen in riding through shallow water by the number of minute globules of it thrown up by the horses feet, which roll far on its surface; and by the difficulty with which small globules of mercury poured on the surface of a quantity of it can be made to unite with it.[Back to Canto]
Spontaneous birth, l. 247. See additional Note, No. [I].[Back to Canto]
In branching cones, l. 259. The whole branch of an artery or vein may be considered as a cone, though each distinct division of it is a cylinder. It is probable that the amount of the areas of all the small branches from one trunk may equal that of the trunk, otherwise the velocity of the blood would be greater in some parts than in others, which probably only exists when a part is compressed or inflamed.[Back to Canto]
Absorb the refluent flood, l. 262. The force of the arterial impulse appears to cease, after having propelled the blood through the capillary vessels; whence the venous circulation is owing to the extremities of the veins absorbing the blood, as those of the lymphatics absorb the fluids. The great force of absorption is well elucidated by Dr. Hales's experiment on the rise of the sap-juice in a vine-stump; see Zoonomia, Vol. I. Sect. XXIII.[Back to Canto]
And from diminish'd oceans, l. 268. The increase of the solid parts of the globe by the recrements of organic bodies, as limestone rocks from shells and bones, and the beds of clay, marl, coals, from decomposed woods, is now well known to those who have attended to modern geology; and Dr. Halley, and others, have endeavoured to show, with great probability, that the ocean has decreased in quantity during the short time which human history has existed. Whence it appears, that the exertions of vegetable and animal life convert the fluid parts of the globe into solid ones; which is probably effected by combining the matter of heat with the other elements, instead of suffering it to remain simply diffused amongst them, which is a curious conjecture, and deserves further investigation.[Back to Canto]
And young Sensation, l. 270. Both sensation and volition consist in an affection of the central part of the sensorium, or of the whole of it; and hence cannot exist till the nerves are united in the brain. The motions of a limb of any animal cut from the body, are therefore owing to irritation, not to sensation or to volition. For the definitions of irritation, sensation, volition, and association, see additional Note [II].[Back to Canto]
Or Mucor-stems, l. 283. Mucor or mould in its early state is properly a microscopic vegetable, and is spontaneously produced on the scum of all decomposing organic matter. The Monas is a moving speck, the Vibrio an undulating wire, the Proteus perpetually changes its shape, and the Vorticella has wheels about its mouth, with which it makes an eddy, and is supposed thus to draw into its throat invisible animalcules. These names are from Linneus and Muller; see [Appendix to Additional Note I].[Back to Canto]
Beneath the shoreless waves, l. 295. The earth was originally covered with water, as appears from some of its highest mountains, consisting of shells cemented together by a solution of part of them, as the limestone rocks of the Alps; Ferber's Travels. It must be therefore concluded, that animal life began beneath the sea.
Nor is this unanalogous to what still occurs, as all quadrupeds and mankind in their embryon state are aquatic animals; and thus may be said to resemble gnats and frogs. The fetus in the uterus has an organ called the placenta, the fine extremities of the vessels of which permeate the arteries of the uterus, and the blood of the fetus becomes thus oxygenated from the passing stream of the maternal arterial blood; exactly as is done by the gills of fish from the stream of water, which they occasion to pass through them.
But the chicken in the egg possesses a kind of aerial respiration, since the extremities of its placental vessels terminate on a membranous bag, which contains air, at the broad end of the egg; and in this the chick in the egg differs from the fetus in the womb, as there is in the egg no circulating maternal blood for the insertion of the extremities of its respiratory vessels, and in this also I suspect that the eggs of birds differ from the spawn of fish; which latter is immersed in water, and which has probably the extremities of its respiratory organ inserted into the soft membrane which covers it, and is in contact with the water.[Back to Canto]