Page:Microscopicial researchers - Theodor Schwann - English Translation - 1947.pdf/98

PUS-CORPUSCLES The low grade of development held by the class of cells now under consideration, in which those elementary formations retain their greatest degree of individuality, is indicated by the fact that it presents so very few modifications. The mucus-, pus-, and lymph-corpuscles are small round cells with a nucleus attached to their walls. According to Henle, mucus- and pus-corpuscles cannot be distinguished in any way from one another, and those of lymph differ from them only inasmuch as their nucleus is more round and granulous, and does not crumble under the action of acetic acid. No difference exists between them in the form of the entire cell. The blood-corpuscles present a higher degree of development in this class. In them we not only find very characteristic cell-contents, the red colouring matter, but the form of the cell also undergoes an important alteration, inasmuch as it becomes flattened. As this flattening takes place in cells which float free in a fluid, it cannot be explained as the result of mechanical causes, but must manifestly be regarded as a peculiar stage of development of these cells. The nucleus is persistent in all these cells, whilst in those more highly developed it usually disappears at some subsequent period. Throughout this class the cytoblastema is a fluid; and it is present in greater quantity than we shall find to be the case in the next class. If the egg be included in this class, we have yet another peculiarity in the cells to be added to the above; viz. that not only have the separate yelk-cells cell-contents consisting of distinct granules, but that the development of the yelk-cells within the yelk considered as one cell, is a formation of cells within cells, and in some of these cells even a second enclosure takes place. This peculiarity, however, is one which may almost be said to stand in inverse ratio to the importance of the tissue. It is most frequent, perhaps indeed universal, in vegetables, occurs more rarely in animals, as in the egg, crystalline lens, cartilage, and so on, and appears to be altogether absent in the higher structures, as areolar tissue, muscle, &c. We have already discussed the other peculiarities of the cells of the egg. In the following class we shall not only find a greater change in the form of the cells. from flattening, but we shall also become acquainted with many other different modifications of them.