We cannot reduce the mystery of life by treating contemptuously its ultimate cells. They are as defiant of interpretation by our present methods as the more complex structures they compose. The mystery of life, _per se_, is as great and as deep, in a monad and a mildew, as in a man. Every attempt to argue away the meaning of vital function and property, on the basis of the organic simplicity of unicellular organisms, is wholly fallacious. It is knowledge, not speculation, which affirms that the least and lowest, as well as the largest and most complex of living forms, are distinguished absolutely from all other kinds of things. There is ‘no link’ between matter living and matter without life. To attempt to build up ‘life’ by slow increments of added complexity, in atomic or molecular structure, is a philosophical ingenuity; but it expresses no natural truth within the horizon of our knowledge. A higher number of primal, or even chemical atoms, arranged in the most complex ratios, and affected by the most rhythmic movements, are not the data from which to deduce a living organism. And to affirm of the lowest living things that ‘they are not, properly speaking, organisms at all,’[19] because the instruments used at a given date did not reveal structure, is, at best, an _argumentum a silentio_; while simultaneously it contradicts the facts of biology, and assumes the whole point at issue. [Footnote 19: _Principles of Biology_, vol. i. p. 482.] On the other hand, there is not a single fact within the present range of our knowledge that indicates, or even suggests, that the quarternary compounds approximate, under any known conditions, to the state of matter living.