​Note 1, p. 125. It is the primal organ, &c.] Philoponus and Simplicius, according to some commentators, believed that the "mind" was the organ or principle here alluded to; but Saint Hilaire is disposed to regard it as "sensibility, irrespective of any thinking principle." Trendelenburg inquires, what means the term 'primal' quid hoc πρῶτον? He seems, however, to consider the mind as the special seat of the faculty in question—"quod primum dicitur, id tacite mentem spectari videtur, quæ propria est hujus facultatis sedes; et ea prima quidem, si ab intimo fonte proficiscaris." It may, however, with some confidence, be assumed that this primal organ points, suggestively, to the brain; for it evidently implies a central organ connected with each of the senses, and receptive of all sentient impressions. Thus, such an organ, while receptive of form, may well be said to be identical with the object; and yet, seeing how opposed are the ​manifestations of the sensibility to the properties of matter, not be so, in an absolute sense. The organ, like the brain, in fact, being perceptive of forms and properties through the senses, is identified, pro tanto, with objects; although it cannot but differ from them absolutely, in mode of being, that is in essence.

Note 2, p. 126. But why do not plants feel, &c.] The answer to this question, by assigning to the organ a definite locality and function, seems to lend support to the explanation offered in the foregoing note. The passage in the original τὸ μὴ ἔχειν μεσότητα is rendered too freely, perhaps, in this version, as mediate faculty; but the French "qualité moyenne" is to the same purport. The Latin is, "neque id medium, tanquam mensuram et modum habent, quo sensus quasi judicant." It may be that as Aristotle had refused, so to say, sensibility to the brain, he found himself constrained, in order to explain the function of the senses and their power of recalling images, to adopt a central organ, to be as well the source of sensibility as the sensorium or store-house, for the mind and memory. He had been led, in fact, to regard the brain as insentient, because of its not imparting sensation when touched, and as subsidiary to the respiration for tempering the internal heat, because of its apparent coldness. All this was the settled conviction of this great man; Democritus, however, seems to have perceived that the brain is either the organ or the seat of sensibility, although the opinion was not generally admitted. ​Plato agreed with physiologists in making the seat of the senses to be the liver and neighbourhood of the heart, but he differed from Aristotle in believing the brain to be continuous with the spinal chord, and to be the source of the intellectual faculties. He held the brain, in fact, to be the seat if not the source of the higher faculties, while he assigned the appetites and coarser passions to the viscera. Hippocrates^[1], who lived some years before him, assigns to the brain the guardianship of the mind, and makes it to be not only the first percipient of all the changes of the seasons, but also the source and seat of all the more deadly and complicated maladies.

Note 3, p. 126. It may be questioned, &c.] The argument, in these passages, is to account for the changes which are constantly going on in bodies, and for which that age could assign no adequate cause; but still it was perceived that tangible and sapid qualities (hot and cold, wet and dry, acid, saline, astringent, and others) must be the agents principally concerned in their production. Thus, although neither light nor darkness, sound nor odour, can act upon bodies, yet something present with them may, and this seems to point, suggestively, to those imponderable and invisible forces (heat, magnetism, electricity, &c.), for which, as yet, even "no plausible theory has been adopted."

Note 4, p. 126. But all bodies are not impressionable, &c.] These passages are very obscure; but their purport ​seems to be, that odour and sound can act only upon such bodies as, like the air and water, are neither limited nor stationary—are made to be the carriers, as it were, of delicate emanations and vibrations to sentient organs. Thus, it is added, the air, having been impressed by odour, readily gives it out, and, then, through the smell, becomes perceptible to the sentient being. But neither odour nor sound, as such, can in aught contribute to the changes to which all inert bodies are subject; and the actions of sound and odour, therefore, seem to be limited to sentient, that is, living properties. This may be to us a truism, but it must be recollected that even to Aristotle the olfactory passages were but imperfectly known; that the opinions upon the Atmosphere were hypothetical; and that the processes by which changes are wrought in inert matter were still to be detected.