1. In primary cultures sarcoma cells exhibit a much greater activity than do normal connective tissue cells grown from the adult blood vessel; there is a shorter latent period, ameboid phenomena are more marked, and cell multiplication proceeds more rapidly.

2. In secondary cultures sarcoma cells are less active than in primary cultures; connective tissue cells, on the other hand, show a markedly accelerated growth.

3. Connective tissue cells are more easily propagated over long periods in vitro than are sarcoma cells; they multiply actively in cultures more than three months old.

4. The method of tissue cultivation is well adapted to the study of normal and pathological cell division; the nuclear changes are easily discernible in the living cell as division proceeds, and staining methods may be applied to verify observations upon the unstained structures.

5. Atypical mitoses of several kinds are found in cultures of sarcoma cells but are not seen in growths of connective tissue.

6. The time required for division in rat connective tissue cells kept at body temperature (38° C.) varies within relatively narrow limits (twenty to fifty minutes); sarcoma cells, on the contrary, exhibit marked variations and several hours may be required.

7. In studies upon living cells amitotic division has not been observed in either normal or tumor tissue. Evidences of nuclear budding, however, with the formation of cells containing several nuclei of irregular size have been noted.3 The development of a cell with two nuclei from a mononuclear cell by mitotic division of the nucleus without division of the cytoplasm has also been observed.

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