Page:Life and death (1911).djvu/174

 *mon element, the cell. Contemporary anatomists, Koelliker, Max Schultze, and Ranvier, have thus established the generality of the cellular constitution, while zoologists and botanists confirm the same law for all animals and vegetables, and exhibit them all as either unicellular or multicellular.

The Cellular Origin of Complex Beings.—At the same time embryogenic researches showed that all beings spring from a corpuscle of the same type. Going back in the history of their development to the most remote period, we find a cell of very constant constitution—namely, the ovule. This truth may be expressed by changing a word in Harvey's celebrated aphorism—omne vivum ex ovo; we now say omne vivum e cellula. The myriads of differentiated anatomical elements whose association forms complex beings are the posterity of a cell, of the ''primordial ovule'', unless they are the posterity of another equivalent cell. The second task of histology in the latter half of the nineteenth century consisted in following up the filiation of each anatomical element from the cell-egg to its state of complete development.

The whole cellular theory is contained in the two following statements, which establish the morphological unity of living beings:—Everything is a cell, everything comes from an initial cell; the cell being defined as a mass of substance, protoplasm or protoplasms, of an average diameter of a few microns.

§ 2. THE SECOND PERIOD: THE DIVISION OF THE CELL.

Second Period: Constitution of the Cell.—This was, however, only the first phase in the analytical study