_Second Period: Constitution of the Cell._—This was, however, only the first phase in the analytical study of the living being. A second period began in 1873 with the researches of Strassburger, Bütschli, Flemming, Kuppfer, Fromann, Heitzmann, Balbiani, Guignard, Kunstler, etc. These observers in their turn submitted this anatomical, this infinitely small cellular microcosm, to the same penetrating dissection their predecessors had applied to the whole organism. They brought us down one degree lower into the abyss of the infinitely small. And as Pascal, losing himself in these wonders of the imperceptible, saw in the body of the mite which is only a point, “parts incomparably smaller, legs with joints, veins in the legs, blood in the veins, humours in the blood, drops in the humours, vapours in these drops,” so contemporary biologists have shown in the epitome of organism called a cell, an edifice which itself is marvellously complex. _The Cytoplasm._—The observers named above revealed to us the extreme complexity of this organic unit. Their researches have shown us the structure of the two parts of which it is composed—the cellular protoplasm and the nucleus. They have determined the part played by each in genetic multiplication. They have shown that the protoplasm which forms the body of the cell is not homogeneous, as was at first supposed. The idea which was mooted later, that this protoplasm was formed, to use Sachs’ words, of a kind of “protoplasmic mud,”—_i.e._, of a dust consisting of grains and granules connected by a liquid,—is no longer accurate. There is a much simpler view of the case. According to Leydig and his pupils, we must compare the protoplasm to a sponge in the meshes of which is lodged a fluid, transparent, hyaline substance, a kind of cellular juice, hyaloplasm. From the chemical point of view this cellular juice is a mixture of very different materials, albumens, globulins, carbohydrates, and fats, elaborated by the cell itself. It is a product of vital activity; it is not yet the seat of this activity. The living matter has taken refuge in the spongy tissue itself, in the _spongioplasm_.