On the Classification of Cells According to Their Inorganic Structure in vitro. 20

One of the greatest difficulties in carrying out any problem in vitro is that of establishing a morphological criterion by which the various cell elements composing the growth can readily be classified. When dealing with pure culture strains of “Fibroblasts” and epithelial cells it is a comparatively simple matter to distinguish between the 2 cell types, as they not only exhibit distinct differences in their morphology, but also in their mode of growth. But when attempting to distinguish these 2 different types of cells in a mixed growth colony it becomes more difficult, as the epithelial elements composing the advancing free edge of the new growth invariably isolate themselves from the epithelial sheet and migrate into the culture medium as separate units, assuming a contour similar to fibroblasts (see Fig. 1). But far greater difficulties confront the investigator when he has to identify cells of the mesenchyme type, such as osteoblasts, chondrioblasts, and heart fibroblasts which, although possessing varying functional activities, exhibit similar morphological values.

Parker and Fischer, 1 realizing this difficulty, successfully demonstrated that mesenchyme elements in tissue cultures, which would be designated morphologically as “Fibroblasts”, are found to possess different inherent growth potencies when cultivated under similar conditions in vitro. On these grounds they rightly contended that “the physiological properties of the cell should constitute the first claims to any definition.”

Recently Horning 2 found that tissue culture cells which exhibit the same morphological characteristics and behavior under normal conditions in vitro, differ, however, in their reactions to similar pathological conditions, as the rate of cytolysis was in all cases found to be dependent upon the inherent growth energy of the given strain.