Toward the end of the seventeenth century, Malpighi and Grew found that organic tissues, placed under the microscope, did not consist of homogeneous substance as they appear to the naked eye, but of small particles separated from each other, which particles have been called cells. But although the cells were discovered, their real importance was far from being understood, or even surmised. This was no doubt the reason for the small interest given to the cell during the eighteenth century, and the small progress cytology made during this whole period. From 1670 to 1830, or more than a century and a half, the cell was known mainly as a saccate body, resembling a hollow tube, and became the subject of more or less wild speculations. A wider interest for the substance and nature of the cell was evoked in the beginning of the nineteenth century by the works of Brisseau de Mirbel, Treviranus, Moldenhaver and several others. Many different parts began to be distinguished within the cells, such as membrane, protoplasm, chlorophyll, etc. These parts were later found to be as many organs in the cell performing different functions, which are at present to some extent defined. The cell previously considered as a saccate body proved to constitute a being endowed with organs, a living organism. According to modern cytology, the cell is a living individual; an elementary organism. Although these beings are so exceedingly minute that the naked eye can observe them only in combinations of thousands and millions, yet each and every one of them not only possesses individual life, but also the organs necessary for sustaining individual existence. Innumerable quantities of such tiny beings build up the organisms of plants and animals. As human individuals form the building material of the body of a community, so the cells form the building material of the bodies of plants and animals. Since the cells bear the same relation to plants and animals as human individuals to a community, every plant and animal then may be considered as a community, a cell-state, where the cells are the citizens. _Every organism, therefore, is a community, and vice versa, every community is an organism._ So far as we have knowledge of the organisms they are all similar in this respect. Plants and animals are communities of individually living cells in the same sense as nations and states are communities of human beings. The individuals in these different communities are of different kinds and degrees of development, but the composition of the organic edifice is in all essential features exactly the same. The differences are literally only apparent, being due as they are to the different aspect they present to our observation.