That this is the correct mode of scientific investigation is seen by the abandoning of the (ontogenetic) vital force. The latter is no longer admitted by anybody, now that we have turned from mere speculation to the investigation of Nature’s processes; nevertheless its non-existence has not been demonstrated, nor are we yet in a position to prove that all the phenomena of life must be traced to purely physico-chemical processes, to say nothing of our being actually able to thus trace them. Von Baer also states “that the abolishment of the vital force is an important advance; it is the reduction of the phenomena of life to physico-chemical processes, although these indeed still contain many gaps.” He points out how very far we are still removed from being able to reduce to physical causes, the processes through which the fertilized yelk of an egg becomes developed into a chicken. How comes it therefore that we all have a conviction that such a complete reduction will in time become possible, or if not this, that the development of the individual depends entirely upon the same forces which are in operation without the organism? For what reason have we rejected the “vital force”? Simply because we see no reason for assuming that known forces are insufficient for explaining the phenomena, and because we are not justified in admitting directive forces as long as we have any hope of one day furnishing a mechanical explanation. But if it is not only permissible, but even necessary, to explain the _ontogenetic_ vital power by known forces, and to commence to indicate the mechanism which produces the individual life, why should it not be equally necessary to abandon that assumption of a _phyletic_ vital force which stifles any deeper inquiry, and to attempt to point out that here also the co-operation of mechanical forces has brought about the multitudinous and wonderful phenomena of the organic world? The renunciation of the old vital force was certainly an immediate consequence of the acquisition of new facts--of the knowledge that the same compounds which compose organic bodies can be produced without the latter. This discovery, due to Wöhler and his followers, showed that organic products could be prepared artificially.[285] In brief, the decline of the vital force followed from the knowledge that at least one portion of the processes of life was governed by known forces.