Knowledge arrives, then, at a certain bankruptcy. It is not very far from this point to that of proclaiming the uselessness of the external world as a means of explaining the nature of knowledge itself. It is only a step from uselessness to reality. The idealistic philosophers who develop their theory to its logical conclusion, can say, without paradox, that everything occurs in vision, for example, as if the object did not exist--as if intelligence, though believing that it receives aid from the eye, in reality created this object just as far as it wishes to know it. The phenomenon of hallucinations gives an appearance of reason to these exasperated idealists. Did not Taine, who was not exasperated, call sensation a true hallucination? But why true? That is a word which, in the circumstances, it is difficult to justify. It would be juster to say that hereditary habit inclines us to regard certain sensations as true, certain others as false. Perhaps utility serves us also as guide, and we imagine, in order to reassure ourselves, an external and fallacious world whose operations correspond to the movements of our psychology. II There is another way of knowing, at once more elementary, more intimate, and more uncertain. This is absorption. The elements of our nourishment, in proportion as we "know" them, disintegrate, yield soluble parts to our organism, and reject the rest in a form equally unknowable. If we reject, as we should, the primitive distinction between soul and body, admitting only the body and believing everything to be physical, then this way of knowing should be studied parallel with those ways which spring from each of our different senses, or from their collaboration. It is certain that absorption has taught man in every age. It is through it, and not by virtue of an unknown instinct, that he has succeeded in separating vegetables and animals into good and bad, into useful and harmful or indifferent. Our analytical methods are still unable, save perhaps in particularly expert hands, to distinguish mushrooms as a harmful or favourable form of nourishment. The expert himself must be guided, for this delicate operation, by a direct and real experiment of absorption. Man, devoid of science, took himself as laboratory. None was surer. He acquired, by this means, certain parts of his knowledge which have proved most useful to humanity and to the domestic animals. From time to time medications are rediscovered which figure in ancient pharmacopeias. Thus formate of lime or of soda, recently prescribed as a muscular invigorant, contains scarcely a principle that did not figure in the old "water of magnanimity," obtained by maceration and distillation of a certain quantity of ants. How did our ancestors, who were no doubt shepherds and labourers, come to distinguish the virtue of ants? Evidently by eating them. The foul Arabs and other low forms of humanity who eat their vermin, find in them, perhaps, an analogous tonic.