On mitosis in proliferating epithelium

Abstract

The object of the present investigation is to determine the character of the mitosis occurring in cutaneous epithelium which has been artificially stimulated to proliferate freely. In the epithelial proliferation of carcinoma, in addition to somatic mitosis, a synaptic mitosis is also met with. In attempting to decide upon the significance to be attached to this latter phenomenon it is necessary to ascertain whether reduction mitosis is met with exclusively in cancerous proliferation of the surface epithelium, or whether it is also encountered in non-cancerous proliferation. If it is present in the latter case, then synaptic mitosis cannot be regarded as exclusively related to epithelioma, or, for that matter, to sexual reproductive tissue; if, however, only somatic mitoses occur in non-cancerous epithelial proliferation, then the possibility is present that the altered biological characters presented by the epithelial cells of malignant growths may be in some way directly connected with the reduction taking place in the number of chromosomes. The abundant epithelial proliferation occurring in many cutaneous diseases, e. g. , psoriasis, lichen planus, and dry forms of eczema, is unsuitable for this investigation, since the amount of material available from such sources is too small and the supply too inconstant to fulfil the requirements of research. Recourse was therefore had to epithelium, which had been made to proliferate freely by the use of scharlach R, dissolved in olive oil, the injection of which beneath the skin of the rabbit’s ear causes extreme and, it may, irregular hypertrophy of the Malpighian layer. It was further found of advantage in obtaining an abundance of division figures to implant pieces of such proliferating epithelium under the skin of the rabbit. Using the material obtained in these two ways the present investigation was carried out. The effect of scharlach R, it may be observed, is to cause marked increase of the prickle layer, both of the surface epithelium and of the hair follicles. This increase is at first fairly regular, but later, when considerable in degree, becomes irregular, and ingrowth of epithelium occurs, comparable to, though considerably less extensive than, that occurring in squamous epithelioma. If the proliferation be set up in scar tissue, the resemblance to the latter condition is striking. With the disappearance of the scharlach R the process comes to an end and involution occurs, though the skin appendages may be more or less destroyed. The character of the epithelial proliferation is, therefore, intermediate between that of such affections as psoriasis and lichen planus, in which epithelial hypertrophy without downgrowth takes place, and epithelioma, in which downgrowth of epithelium is the characteristic feature, and is the means by which neighbouring tissues are invaded and extension of the growth occurs.