necessary to life in itself, hence they enter as food and become transformed into protoplasm. The lowest forms of life with which we are acquainted are nothing but simple pieces of protoplasm and yet they have all the appearance of living objects.
But in what consist these signs of life which are common to all living objects? In this, that the protoplasm takes from its surroundings other matter suitable to itself and assimilates it while other former portions of the body become decomposed and are thrown off. Other things, not living bodies, decompose or make combinations, but cease thereby to be what they were. The rock worn by atmospheric action is no longer rock, the metal which becomes oxidised goes off in rust. But what causes the destruction of dead bodies is the essential of the existence of living protoplasm. From the very moment when the unbroken interchange in the constituents of protoplasm ceases, the continual interchange of receiving and throwing off, from that moment the protoplasmic substance itself ceases, becomes decomposed, that is, dies.
Life, the mode of existence of protoplasmic substance, therefore consists in this, that at one and the same moment it is itself and something else, and this is not the result of a process to which it is compelled by external agency, since this may happen also with objects which are dead. On the contrary life, which is change of matter, is consequent upon nourishment and throwing off, is a self-fulfilling process inherent in its medium, protoplasm, without which it cannot exist. Hence, it follows that if chemistry should ever discover how to make protoplasm artificially, this protoplasm must show some signs of life, even if very insignificant. It is, of course,
