repeatedly indicated before, all the cells stand in actively reciprocal relations with each other. We have plenty of proofs for the acceptance of this view; while, on the other hand, we have no clear insight, at present, into the signification of this reciprocal dependence. Probably unicellular organisms alone are wholly dependent upon themselves. They perform all the processes necessary for life independently of other cells, except when, as sometimes happens, a conjunction of these simple organisms rises to the level of a symbiosis. The latter, as we have already pointed out, must have a value corresponding exactly to the reciprocal interactions of the cells of the more highly organized forms of the vegetable and animal kingdoms. For there is no doubt that in plants, too, the cells have actively reciprocal relations.
Doubtless there are, in an organism composed of cell groups, numerous kinds of cells which can live without having reciprocal relations with other cells, exactly in the same way as a single individual can isolate itself from its stock and still continue life for a certain time. But in the same manner as the well-being of a people or a State finally depends upon the regular collaboration of the many, so each kind of cell expresses its full value only by associating its work with that of the other cells in the organism. Only then is a cell capable of developing all its capacities. In many particular functions, indeed,
