De praecipius visus symptomatis eorumque causis Physica & Medica contemplatio

XX.
From this it is clear why Nature endowed some parts with a more exquisite sense and others with a more obtuse one, namely, not only from the frequent propagation of the nerves but also from the very substance of the spirit, which, affected differently in different parts, also changes the power of sensing.

XXI.
The animal spirit is formed from the vital spirit in two ways, kata psyxin by cooling and kata pyxin by condensation. For in the animal body, the vital spirit is the most fervent of all, hois zesis thermos zotike as a living, hot boiling, whence it is also accustomed to be called pyr zotikon vital fire by the philosophers; although it possesses much in the tenuity, purity, and brightness of its substance, nevertheless, due to the excess of heat and its perennial agitation, it does not obey the function of the senses, in which the peaceful and sedate symmetria symmetry/proportion of various faculties thrives.

XXII.
The brain, therefore, obtained a cooler temperature than the heart, so that, by placating the fervor, it might reconcile a middle nature for the spirit, and gather the scattered parts into itself, by which mutual struggle both the labile and the solid organ might emerge, apt for various impressions. The pyxis condensation also served to increase the light, because by the testimony of the opticians, condensed light is stronger than dispersed light, as in the stars.

XXIII.
Furthermore, we have assigned a middle eukrasia good temperament to the animal spirit, not only by reason of the primary qualities, but also of the whole essence: which, on account of its remarkable brightness, as a rival of the higher bodies, hos analogon ti ton astron stoicheion as a certain element analogous to the stars, attacks the limbs with no sense of either cold or heat.

XXIIII.
By the dryness of its principle, namely the vital, it has for the most part retained its nature, although softened by a thin humidity, so that it might cherish impressed images more persistently, and not shake them off again by an unstable flow at any moment. Moreover, it seems to have no small affinity with the supreme bodies, because it obtained its station nearest to the heavens in the Fire, and light, although apoios without quality, is established by physicists as more dry than humid.