《Natural History（5 自然史第5卷）》：

　　THE interior man is double， being composed of two principles different in their nature， and contrary in their action. The soul， that principle of all knowledge， is perpetually opposed by another purely material principle. The former is a pure light， accompanied with serenity and peace， a salutary source， whence flow science， reason， and wisdom； the latter is a false light， which never shines but in the midst of darkness and hurricane， an impetuous torrent fraught with error and passion.

　　The animal principle is first developed. As it is altogether material， and consists in the duration of vibrations， and the renovation of impressions formed in the internal material sense， by objects analogous， or contrary to our appetites， it begins to act as soon as the body is capable of feeling pain or pleasure. The spiritual principle manifests itself much later， and is developed and perfected by means of education； it is by the communication of the thoughts of others that the infant becomes a thinking， a rational being； and without this communication it would be fantastic or stupid， according to the degree of activity or inactivity of its internal material sense.

　　Let us consider a child， when at liberty， and far from the eye of his master. By his exterior actions we may judge of what passes within him. A stranger to thought or reflection， he acts without reason； treads with indifference through all the paths of pleasure； obeys all the impressions of exterior objects； amuses himself like a young animal， in running and bodily exercise； all his actions and motions are without order， or design. Called on by the person who has taught him to think， he composes himself， directs his actions， and proves that he has retained the thoughts which have been communicated to him. In infancy， the material principle is predominant， and would so continue， were not education to develop the spiritual principle and to put it in motion.

　　The existence of these two principles is easily discovered. In life there are moments， nay， hours and days， in which we may not only determine of the certainty of their existence， but also of the contrariety of their action. I allude to those periods of languor， indolence， or disgust， in which we are incapable of any determination， when we wish one thing and do another； I mean that state， or distemper， called vapours； a state to which idle persons are so peculiarly subject. If in this situation we observe ourselves， we shall appear as divided into two distinct beings， of which the first， or the rational faculty， blames every thing done by the second， but has not strength sufficient effectually to subdue it； the second， on the contrary， being formed of all the illusions of sense and imagination， constrains， and often overwhelms the first， and makes us either act contrary to our judgment， or remain inactive， though disposed to action by our will.

　　While the rational faculties reign， we are calmly occupied with ourselves， our friends， and affairs. But when the material principle prevails， we devote ourselves with ardour to dissipation， to all the pursuits and passions it creates； and are hardly capable of reflecting upon the very objects by which we are so engrossed. In both these states we are happy； in the former we command with satisfaction， and in the latter， we are still more pleased to obey. As only one of these principles is then in action， and acts without opposition from the other， we feel no internal contrariety； our self appears to be simple， because we experience but one impulse. In this unity of action consists our happiness； for， whenever our reason condemns our passions， or， from the violence of our passions， we attempt to discard reason， from that minute we cease to be happy； the unity of our existence， in which consists our tranquillity， is destroyed； the internal contrariety commences， and the two contending principles are manifested by doubts， inquietude and remorse. Of all states， that is the most unhappy in which these two sovereign powers of human nature are both in full motion， and produce an equilibrium. Then it is man feels that horrible disgust which leaves no desire but that of ceasing to exist， no power but to effect his own destruction， by coolly plunging into himself the weapons of despair and madness. What a state of horror! in its blackest colours it is here presented； but by how many gloomy shades must it be preceded?

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