after their brain has been removed. Now, if our surest experience teaches us that _the will_, which is known to us in most immediate consciousness and in a totally different way from the outer world, is the real agent in actions attended by consciousness and directed by the chief centre of the nervous system; how can we help admitting that those other actions which, proceeding from that nervous system but obeying the direction of its subordinate centres, keep the vital processes constantly going, must also be manifestations of _the will_? Especially as we know perfectly well the cause because of which they are not, like the others, attended by consciousness: we know, that is to say, that all consciousness resides in the brain and therefore is limited to such parts as have nerves which communicate directly with the brain; and we know also that, even in these, consciousness ceases when those nerves are severed. By this the difference between all that is conscious and unconscious and together with it the difference between all that is voluntary and involuntary in the movements of the body is perfectly explained, and no reason remains for assuming two entirely different primary sources of movement: especially as _principia præter necessitatem non sunt multiplicanda_. All this is so obvious, that, on impartial reflection from this standpoint, it seems almost absurd to persist in making the body serve two masters by deriving its actions from two radically different origins and then ascribing on the one hand the movements of our arms and legs, of our eyes, lips, throat, tongue and lungs, of the facial and abdominal muscles, to the will; while on the other hand the action of the heart, the movements of the veins, the peristaltic movements of the intestines, the absorption by the intestinal villi and glands and all those movements which accompany secretion, are supposed to proceed from a totally different, ever mysterious principle of which we have no knowledge, and which is designated by names such as vitality, archeus, _spiritus animales_, vital energy, instinct, all of which mean no more than _x_.[201] [201] It is especially in secretive processes that we cannot avoid recognising a certain selection of the materials fitted for each purpose, consequently a _free will_ in the secretive organs, which must even be assisted by a certain dull sensation, and in virtue of which each secreting organ only extracts from the same blood that particular secretion which suits it and no others: for instance, the liver only absorbs bile from the blood flowing through it, sending the rest of the blood on, and likewise the salivary glands and the pancreas only secrete saliva, the kidneys only urine, &c. &c. We may therefore compare the organs of secretion to different kinds of cattle grazing on one and the same pasture-land, each of which only browses upon the one sort of herb which suits its own particular appetite. [Add. to 3rd ed.]