The healing of a wound is a process essentially similar to the regeneration of the lens. Normally the cells which begin to proliferate after a wound is made in the skin lie dormant, inasmuch as they neither grow nor divide. When a wound is made certain layers of epidermal cells undergo rapid cell division. Leo Loeb[174] has studied this case extensively. He found that if the skin is removed anywhere, epidermis cells from the wound edge creep upon the denuded spot and form a covering. This may be a tropism (stereotropism) or it may be a mere surface tension phenomenon. Next a rapid process of cell division begins in the cells adjacent to the wound these cells having been heretofore dormant. He is inclined to attribute this increase in the rate of cell division to the stretching of the epithelial cells, and he is supported in this reasoning by the observation that the larger the wound the more rapid the process of healing.[175] During wound healing the mitoses first increase markedly in the old epithelium. With the closure of the wound a sudden fall in the mitoses takes place. The closure of the wound causes an increase in the number of epithelial rows over the defect. This increase is therefore reached at an earlier period in the larger wound since the process of mitosis is more rapid here. Leo Loeb thinks that the pressure of the epithelial cells upon each other leads to a rapid diminution in the mitotic proliferation.[176] [174] Loeb, Leo, _Arch. f. Entwcklngsmech._, 1898, vi., 297. [175] Spain, K. C., and Loeb, Leo, _Jour. Exper. Med._, 1916, xxiii., 107; Loeb, L., and Addison, W. H. F., _Arch. f. Entwcklngsmech._, 1911, xxxii., 44; 1913, xxxvii., 635. [176] The excessive formation of epithelial cells in the healing of wounds has led the older pathologists to the generalization that if something is removed in the body an excessive compensation will take place. The formation of antibodies has even been explained on this basis by Weiggert and Ehrlich in their side-chain theory. As a matter of fact, this generalization is entirely incorrect and in regeneration of starfish, actinians, flatworms, annelids, and possibly in all forms the reverse is true; _e. g._, if we cut off the anterior half of the body in _Cerianthus_ less is reproduced than was cut away namely only tentacles and the mouth, but not the missing piece of the body. Weiggert’s conception of regeneration was probably based on the phenomenon of the healing of wounds, but the excessive epithelium formation in this case is not the expression of a general law of regeneration but of the peculiar mechanical conditions which lead to mitoses. It would be a very strange coincidence indeed if a theory of antibody formation based on such an erroneous generalization should be correct. Should it be possible that this is more generally the case, _e. g._, also in the lens after it has reached a certain size? The conditions limiting growth require further investigation.