Thus we see that the attack upon the vitalist sanctuary has commenced. But it would be a grave mistake to suppose that final cause and vital force are on the point of being dislodged from their entrenchments. Philosophical speculation has an ample field before it. Its frontiers may recede. For a long time yet there will be room for a more or less modernized vitalism. § 2. THE PHYSIOLOGICAL DOMAIN PROPERLY SO CALLED. Vitalism is even found installed in the region of physiology, although for the moment this science limits its ambition to the consideration of the completely constructed organized being, perfected in its form. The explanation of the working of this constituted machine cannot be complete until we take into account the harmony and the adjustment of its parts. _Harmony and Connection of Parts: Directive Forces._—These constituent parts are the cells. We know that the progress of anatomy has resulted in the cellular doctrine—_i.e._, in the two-fold affirmation that the most complicated organism is composed of microscopic elements, the cells, all similar, true stones of the living building, and that it derives its origin from a single cell, egg, or spore, the sexual cell, or cell of germination. The phenomena of life, looked at from the point of view of the formed individual, are therefore harmonized in space; just as, regarded from the point of view of the individual in formation and in the species, they are connected in time. This harmony and this connection are in the eyes of the majority of men of science the most characteristic properties of the living being. This is the domain of _vital specificity_, of the _directive forces_ of Claude Bernard and A. Gautier, and of the _dominants_ of Reinke. It is not certain, however, that this order of facts is more specific than the other. Generation and development have been considered by many physiologists, and quite recently by Le Dantec, as simple aspects or modalities of nutrition or assimilation, the common and fundamental property of every living cell.