3. That no sensation is possible without a suitable organic substance. Sight can by no means exist without the eye, hearing without the ear, taste without the tongue, smell without the pituitary membrane. And in like manner as the external senses cannot exist without a suitable organic substance, that is, without organs, so neither can the internal senses. The organic substance of perception is the cortical gland, and that of intellection is the simple cortex-as pointed out above [no. 2]. It is altogether repugnant to nature that anything sensitive and intellectual can have existence apart from a suitable substance; for sensations are merely forces and modifications going forth from the substances acted upon. For this reason, the soul is the only sentient and intelligent substance in its body.
