Eliot R. Clark

INTERCELLULAR SUBSTANCE IN RELATION TO TISSUE GROWTH

The tissue growth under discussion is that which occurs in adult tissues: such growth as is involved in wound healing, in the late “reparative” stages of inflammation, or in such tissue overgrowths as are found in elephantiasis. The data have been obtained largely from the direct microscopic observation of growing tissue, as seen in various types of double-walled transparent chambers inserted in the ears, mainly of rabbits:* but to a minor extent, of dogs. What occurs, following the installation of such a chamber in the ear of a rabbit, that involves the two phases of growth, (a) the migration and division phase, and (b) the differentiation phase? Within a few hours, the Ringer’s solution left in the chamber is replaced by an inflammatory exudate.l* There is usually a complete fibrin network, although this may be absent or incomplete. There are usually many extravasated erythrocytes, single or in masses, but these may be absent. There are always leucocytes, mainly polymorphonuclear (neutrophiles or, in the rabbit, pseudo-eosinophiles) , monocytes, and lymphocytes. In the interstices of the fibrin there is clear substance. In some places, this contains suspended cells, which are moved to and fro as a result of changes in the circulation, indicating a fluid consistency; in other places, there is absence of movement, suggesting a viscous or semi-solid condition. This clear material, even when liquid a t first, becomes viscous for a distance approximately 3/10 mm. beyond the last circulating capillary, as the new tissue invades the chamber. That the fibrin may play an important supporting role is indicated in certain chambers in which small growths of epidermis invade the chamber area ; for differentiating epidermis, apparently, contains a fibrinolytic ferment, since it is always accompanied by a dissolution of the fibrin: which is followed by a retraction of the tissue. Also, in the dog, fibrin, if present, is lost early, and the new growths of tissue