The soul and the cells must have something in common that is of a purely spiritual nature. As the spiritual always is a comprehending substance with nothing but comprehensions as its content, the something common to both must consequently have the form of common comprehensions. Not all comprehensions, however, incite to activity and a smaller number yet call forth a co-operation of independently living individuals. But, obviously, the perceptions that concern us now must be of the latter kind. The comprehensions in general that induce a being to activity we call wants or appetites. In its desires a being conceives its own ego in want of one thing or other. The feeling of discomfort, accompanying the want, naturally causes the endeavor to satisfy the want through a corresponding effort. The incitement to activity then is purely spiritual. Are the soul of man and the cells subject to such common needs, requiring their co-operation? If so, at least their wants or appetites cannot be wholly congruous. Such are only to be found in entirely similar beings. But different wants are satisfied in different ways; each requires a carefully adapted form of activity. All direct, immediate co-operation of the soul and the cells is therefore impossible. Only man with man, or cell with cell, can co-operate in the primary sense of the word. But an indirect working alliance is not yet precluded. Though themselves different, the two beings may comprehend wants identical in substance, but not in form. The formal discrepancy would require not only different modes of satisfying the need, but also different kinds of activity; but the common substance might yet under certain conditions so unite and interlink the different labors, that the result would show a mutual co-operation. We shall presently see that the soul and the cells are so united with each other that _the connecting link is the organism per se_. From the point of view of the cells the organism, with its different members and organs, was nothing but the collective expressions of individual wants. Now man comprehends as his needs only the wants of the organs; in other words, the collective wants of the cells are the individual wants of the soul. Experience teaches us that the soul has no direct comprehension of the cells, but only of their organic unions. To prove this it may be sufficient to point out that before the discovery of the microscope, man knew absolutely nothing of the existence of these beings, much less that they were the all-governing forces in his own body. But also in other ways we may ascertain that the comprehending power of the soul does not reach beyond the organs. This is apparent from the different significance the physiological processes have for the soul and for the cells. If we consider the most important of them all, our nutrition, and ask ourselves for whom the nourishment is really intended, we find that it is for the cells and for the cells alone.