Scientia Sinica

118 SCIENTIA SINICA Vol. V

stances contained in them, more in the deep-stained ones, and fewer in the light ones. This picture indicates the development of the disintegrating tissues into deep-stained aggregates, which, in turn, into light-stained aggregates. During the development, the colour of the disintegrating tissues gradually faints, structures gradually make their appearance and young nuclei are formed (same figure, C). Afterwards, cytoplasm takes shape in the periphery, but the cell boundary is still indistinct; it now becomes a young cell (same figure,

D).

At the tip of the growing epidermis the newly formed young nuclei are comparatively smaller. As indicated in fig. 3, Plate V, the upper part is the scab, and under the scab the new epidermis grows from left to right. At the tip of growth, there are very small young nuclei, which contain nuclear substance derived from disintegrating leucocytes.

At the tip of the growing epidermis, there are sometimes young cell nuclei and young cells. In fig. 2 of Plate II one may find, in the new epidermis growing from left to right, a large round young cell (Plate II, fig. 2, A) and a small spindle-shaped young cell nucleus. Their difference is striking.

These young nuclei and cells of different sizes could not be possibly derived from the pre-existing epidermal cells, instead, they are formed of the mixed disintegrating substances in the wound through very complex bio-

chemical processes. Further histological evidences for this assumption are stated below:

(4) Changes of macrophages in the wound. Macrophages are shown in the specimens by vital staining method. They, too, first undergo disintegration in the wound under the scab, and mix together with the disintegrating collagenous fibres and leucocytes. Figure 3 of Plate I is a photomicrograph of lower magnification. The upper part is a deep-stained scab, under which and in front of the growing epidermis (A, B) there are many dark blue granules. When observed in a highly magnified photomicrograph (Plate I, fig. 4, A), they indicate the presence of macrophages. Many of these macrophages around the tip and the inner side of the epidermis have already been disintegrated, and the dark blue granules are released in masses, mixing together with the disintegrating leucocytes (same figure, D). A close examination of the new epidermis shows that at its tip residual trypan-blue granules are still contained in the two not yet well formed young nuclei (same figure, B). Tracing back along the growing tip against the direction of growth, one may find a well-formed young nucleus (same figure, C). The two young nuclei in the region B are still in the developing stage. Epidermal cells do not possess the ability of phagocytosizing the trypan-blue dye; con- . sequently, the two young nuclei are developed from the disintegrating substances of macrophages and leucocytes.

(5) Changes of cartilageous tissue after the penetration of the growing epidermis. The growth of the new epidermis into the cartilage is very rapid.