Hitherto Unpublished Works, Fascicle 14

instrument, as is clear from the second book of On the Soul: Aristotles treatise De Anima, which explores the nature of life and perception original: "de Anima". This is because the other senses do not have an internal medium. For this reason, whether they possess only a nerve or something else, that other thing is not a medium but an instrument that is first changed. This is quite necessary to moderate the action of the perceptible object upon the sense. As it is proven in the first book of On Perspective: a foundational work on optics, likely referring to the Persian scholar Alhazen or Bacon's own earlier writings original: "Perspective", sensation never occurs without a painful suffering: the Latin passio dolorosa refers to a physical alteration or "undergoing" that, in its extreme, causes pain original: "passione dolorosa". This is only consciously perceived when the stimuli are extreme. These external structures also exist to avoid many dangers from air, vapors, dust, smoke, and similar things, lest they harm the primary power.

Indeed, the more noble the powers are, although they can perform wonderful operations while in their proper state, they do not tolerate accidental injuries. If these occur, they fail immediately and more quickly than less noble powers. This is evident in the heart. Aristotle says in the thirteenth book of On Animals that the heart, above all internal members, cannot endure great pain or serious illness. It is similar for the eye in relation to other parts of the body, and for the sanguine temperament: a physical makeup dominated by the element of blood, considered the most balanced and noble in medieval medicine original: "complectione sanguinea" in relation to others. Therefore, nature devised other organs for the primary organs and powers to be changed first. These encounter dangers and injuries for the safety of the primary organs. This is especially true for sight because of its nobility, as will become clear.

In the nerve, however, the primary instrument necessarily resides with respect to all other parts outside the heart. This is because the specific organs are connected to the heart, which is the first sensing thing: the primum sensitivum, or the central point of all biological awareness in Aristotelian biology original: "primum sensitivum". They can only be connected through the nerve. For this reason, the primary organ exists specifically at the nerve.

Since there is general mention of the organs of sensing, it must be understood that the most noble perfection and the final harmony: the balanced ratio of elements and qualities that allows a living thing to function original: "armonia" beneath the soul is the middle proportion and nature of its own sensible objects. Aristotle says in the chapter on touch that touch is a middle proportion of tangible things. He says in the same place that sight is a middle proportion of white and black. Later he says in the same book that within the organ there is a harmony and proportion of its own sensible objects. This is destroyed by an extreme stimulus, just as the harmony in the sound of strings is destroyed by an extreme striking of the strings. He also says that plants do not have sensation because they do not have that spiritual middle nature. In this context, "spiritual" refers to the subtle, invisible "spirits" or vapors that medieval scientists believed carried sensory information through the nerves.