Note 201 — ON THE WILL IN NATURE. [190]

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.]