597. Lastly, those also are in error, who conclude that because an animal performs movements, which are effected by the cerebral forces alone, without the co-operation of the vis nervosa, all its animal forces are actions of the cerebral forces (590, 593). This is the error of the Stahlians, who consider all animal movements to be sentient actions, nay, to be meditated acts of a will, of which the soul is necessarily unconscious. The old error, lately renewed by Whytt, is also connected with this erroneous supposition, namely, that the souls of animals are distributed throughout their bodies by means of the nerves, because animal movements, which are usually sentient actions, can be excited in decapitated animals, thus assuming that no other force than the mental can effect this.

PART III.

ANIMAL NATURE CONSIDERED AS A WHOLE.

INTRODUCTION.

598. THE cerebral forces and the vis nervosa are essential constituents of the proper animal nature of animal organisms (6, 356), and in the more perfect animals are in close connection (591-593). The aggregate of those animal forces, which act naturally in connection in an animal body, constitute its whole animal nature, and this whole is now to be considered; its two essential constituents even in the most perfect, having been discussed in the two preceding parts.

599. The arrangement of this part is as follows:-first, the character of the whole animal nature of an animal will be sketched; secondly, the existence of distinct classes of animals will be proved; then the origin of animals according to their nature will be considered; next, animal life and its natural periods up to its full development; then the system of forces necessary to animal life, or how they act with and through each other for its maintenance and perfection; and, finally, old age and death will be treated of in succession.

CHAPTER I.

ON ANIMAL NATURE IN GENERAL.

600. An organism, which, in its entire and natural condition, is regulated by the animal moving forces of its own proper animal machines, is termed a living animal organism, an animal endowed with life, an animal in the widest sense. In determining the general characteristic distinction of plants and animals, by which we decide whether an organism belongs to the one or the other division, we have to determine whether it is moved in its natural condition, according to the known physical or mechanical laws of gravity, of the force of attraction, of elasticity, of the mechanism of its structure, &c.; or, according to peculiar laws :—whether a touch, or an external impression upon it, excites it to the movement that we should be led to expect from the known physical and mechanical laws of motion, or whether a movement is excited thereby, which compels us to recognise the phenomena of a peculiar force put into action by this external impression; and which regulates it according to other and widely different laws. It is not denied that this distinction is always somewhat indefinite, still it exists in nature, and we universally form a judgment thereon; but we only become more definite, when we have become acquainted with the laws of the animal moving forces. If some persons distinguish animals from plants by their voluntary movements, others by their instinctive actions, and others by their external sensations, it all comes to the same thing; inasmuch as we recognise a moving force in animals differing altogether in its nature from physical and mechanical forces, and acting according to altogether different laws. But these distinctions are wholly deduced from the phenomena of the cerebral forces, while the nerves themselves possess peculiar animal forces, which are not taken into consideration; so that they who adopt this as an universal distinction, are at a loss when they come to decide, whether a certain organism which cannot

possibly be endowed with cerebral forces, be a plant or an animal. Hence the confusion of ideas, caused by the researches on decapitated animals, moved solely by the vis nervosa,-by the phenomena of anencephalous infants born alive-and by animals so constituted by nature, as to live without head or brain, and which manifest no traces of mind; regarding all which no definite opinion can be stated. If, however, the above general distinction be adopted, no difficulty arises in such cases; for, although entirely without conceptions, all these organisms are regulated by external impressions, in a way wholly different from plants, and according to wholly different laws. Now, since we recognise the existence of the vis nervosa of external impressions in animal machines [the brain and nerves], and know that it is adapted to sentient animals, and excites in them the same movements, according to the same peculiar laws as external impressions excite in these organisms; and since we find machines in the latter, which are very similar to the animal machines [brain and nerves] of sentient animals, we can positively decide, that all these organisms are moved animally by nature, by means of animal machines, and that they also belong to the class of animal bodies.

The

601. Still, as has been said, the line of distinction is always indefinite, and the limits of the animal and vegetable kingdoms run so into each other, that they cannot be defined. fault, however, is not in the want of grounds of distinction, but in the difficulty of discovering them in many cases. The movements excited in the sensitive plant by a touch, leads us to the conclusion that it is a zoophyte; so fixed is the principle in us, that an organism must be an animal which is moved by certain impressions-not according to physical and mechanical laws but according to the laws of movement in animals. But these movements are neither sentient actions nor nerve-actions, for upon investigating the structure of the leaf, it is found that the closing of the leaves is simply a mechanical action, excited by a touch.

602. The question may arise, however, whether a body may not be animal in its nature, and yet not be an animal; as, for example, in the case of a decapitated animal. A man, deprived of his limbs, is not the less a man; and so if the vis nervosa continue in a mutilated creature, it is still an animal. Besides,