Some changes in the dying cell

By ordinary transmitted light the nucleus of the living cell is an optically homogenous body lying in a cytoplasm which is more or less granular. The optical difference between the nucleus and the cytoplasm is more strikingly shown by dark field illumination where the nucleus appear optically empty, whereas the cytoplasm scintillates with bright spots. The cytoplasm has, therefore, been considered to be distinctly heterogeneous in contrast to the optically homogenous nucleus. That this is not true may be seen in the following experiment: By means of the centrifuge the cytoplasmic granules of the sea urchin egg can be driven to one side of the egg. On cutting away this part one may obtain an egg fragment consisting of protoplasm which is transparent and optically empty, even when viewed with dark field illumination. This fragment is fully capable of developing. We must, therefore, conclude that the cytoplasm may be as optically structureless as the nucleus. When the cell dies, however, a difference in structure with the dark field illumination becomes at once apparent. Coagulating agents, which are not violent in their reaction, such as gentle heat or weak formalin, make the cytoplasm diffusely milky in appearance, owing to the formation of closely packed and uniformly sized spherules. In the sea urchin egg these globules are about 1 micron in diameter. In tissue cells they are somewhat smaller. The coagulating nucleus in the dying cell, on the other hand, gives a different picture. Here also uniformly sized granules make their appearance but, instead of being evenly distributed, they collect into granular strands which run together to form a nuclear network.