15. That we are ignorant of one or more of the indispensable conditions symbolized in the abstract term Vitality or Vital Force, is no reason for quitting the secure though difficult path of Observation, and rushing into the facile but delusive path of Fiction, which proposes metempirical Agents (in the shape of Vital and Psychical Principles) to solve the problems of Life and Mind. We may employ the term Vital Force to label our observations, together with all that still remains unobserved; and we are bound to recognize the line which separates observation from inference, what is proved from what is inferred; but while marking the limits of the known, we are not to displace the known in favor of the unknown. It is said that because of our ignorance we must assume these causes of Life and Mind to be _unallied_ with known material causes, and belonging to a different order of existences. This is to convert ignorance into a proof; and not only so, but to allow what we do not know to displace what we do know. The organicist is ready to admit that much has still to be discovered; the vitalist, taking his stand upon this unknown, denies that what has been discovered is really important, and declares that the real agent is wholly unallied to it. How _can_ he know this? He does not know it; he assumes it; and the chief evidence he adduces is that the ordinary laws of inorganic matter are incapable of explaining the phenomena of organized matter; and that physical and chemical forces are controlled by vital force. I accept both these positions, stripping them, however, of their ambiguities. The laws of ordinary matter are clearly incompetent in the case of matter which is not ordinary, but _specialized_ in organisms; and when we come to treat of Materialism we shall see how unscientific have been the hypotheses which disregard the distinction. The question of control is too interesting and important to be passed over here. VITAL FORCE CONTROLLING PHYSICAL AND CHEMICAL FORCES. 16. The facts relied on by the vitalists are facts which every organicist will emphasize, though he will interpret them differently. When, for example, it is said that “Life resists the effect of mechanical friction,” and the proof adduced is the fact that the friction which will thin and wear away a dead body is actually the cause of the thickening of a living--the skin of a laborer’s hand being thickened by his labor; the explanation is not that Life, an extra-organic agent, “resists mechanical friction”--for the mechanical effect is _not_ resisted (the skin is rubbed off the rower’s hand sooner than the wood is rubbed off the oar)--but that Life, i. e. organic activity repairs the waste of tissue.