1, 2, 3, 4, 5, 6, 7, 8, 9, the second, &c. ribs with the corresponding dorsal (sentient) nerves, a, b, c, d, e, f, g, h, going out to supply their respective organs with sensation.
C D E, a portion of the main trunk of the organic (non-sentient) nerve, commonly called the Great Sympathetic.
F G H, the membrane of the spinal cord cut open and exposing I K, the spinal cord itself, L, the anterior branch of one of the dorsal nerves, arising from the anterior surface of the spinal cord by several bundles of fibres.
M, the posterior branch of the same nerve, arising in like manner from the posterior surface of the spinal cord by several branches of fibres.
The anterior and posterior branches uniting to form one trunk N.
Two branches, P Q, sent off from the spinal (sentient) trunk to unite with the organic (non-sentient) trunk.
R S T U V W, other branches of the sentient, connected with the branches of the non-sentient nervous trunks in the same mode.
X Y, the main trunk of the sympathetic (non-sentient) nerve cut across and turned aside, in order that the parts beneath it (P N) may be more distinctly seen.
From this description, it is apparent that each sentient nerve, before it goes out to the animal organs, to which it is destined to communicate sensation, sends off two branches to the organic or the non-sentient. These sentient nerves mix and mingle with the insensible nerves; accompany them in their course to the organic organs, and ramify with them throughout their substance. It is manifest, then, that sentient nerves, that nerves not necessary to the organic processes, having, as far as is known, nothing whatever to do with those processes, enter as constituent parts into the composition of the organic organs. What is the result? That organic organs are rendered sentient; that organic processes, in their own nature insensible, become capable of affecting consciousness. What follows? What is the consciousness excited? Not a consciousness of the organic process. Of that we still remain wholly insensible. Not simple sensation. The result uniformly produced, as long as the state of the system is that of health, is pleasurable consciousness. The heart sends out to the organs its vital current. Each organ, abstracting from the stream the particles it needs, converts them into the peculiar fluid or solid it is its office to form. The stomach, from the arterial streamlets circulating through it, secretes gastric juice; the liver, from the venous streamlets circulating through it, secretes bile. When these digestive organs have duly prepared their respective fluids, they employ them in the elaboration of the aliment. We are not conscious of this elaboration, though it go on within us every moment; but is consciousness not affected by the process? Most materially. Why? Because sentient mingle with organic nerves; because the sentient nerves are impressed by the actions of the organic organs. And how impressed? As long as the actions of the organic organs are sound, that is, as long as their processes are duly performed, the impression communicated to the sentient nerves is in its nature agreeable; is, in fact, THE PLEASURABLE CONSCIOUSNESS WHICH CONSTITUTES THE FEELING OF HEALTH. The state of health is nothing but the result of the due performance of the organic organs: it follows that the feeling of health, the feeling which is ranked by every one among the most pleasurable of existence, is the result of the action of organs of whose direct operations we are unconscious. But the pleasurable consciousness thus indirectly excited is really the consequence of a special provision, established for the express purpose of producing pleasure. Processes, in their own nature insensible, are rendered sentient expressly for this purpose, that, over and above the special object they serve, they may afford enjoyment. In this case, the production of pleasure is not only altogether gratuitous, not only communicated for its own sake, not only rested in as an ultimate object, but it is made to commence at the very confines of life; it is interwoven with the thread of existence: it is secured in and by the actions that build up and that support the very framework, the material instrument of our being.