Summing up the results from the former studies (Makino and Yosida 1951, Makino and Kanô, 1951) together with those of the present investigation, it can be concluded that there exists a strain of tumor cells which multiply with a regular mitotic behaviour and participate primarily in the growth of the tumor. These tumor cells possess a peculiar chromosome complex characteristic of this tumor, not only in the number of chromosomes but also in their morphological features. They contain well-balanced subdiploid chromosomes, 40 or thereabouts in number; the chromosome complex is provided with two distinct sets, probably dissimilar in both structure and nature. One of the sets consists of rod-shaped chromosomes ranging from 22 to 24 in number; they seem to originate from the cells of the host on account of their morphological likeness. The other set comprises J- and V- elements of varying sizes, about 16 to 18 in number, which are unknown in their origin because there are no corresponding elements in the host cells. On account of this characteristic peculiarity, the chromosomes of these tumor cells are markedly differentiated from those of the host cells. Furthermore, there has been demon strated no transitional type of chromosomes between normal cells and tumor cells.
The individuality of chromosomes in the strain cells of the tumor remains unchanged through successive transplant generations from host to host. The tumor cells showing mitotic abnormalities of common occurrence are evidently derivatives from these strain cells; they were produced through abnormal mitosis due to the alteration of normal spindle mechanism, the structural change of chromosomes and other unknown causes. On the basis of the above findings, the behavior of tumor cells through a transplant generation have been described in the present paper.
Critique was offered on various hypotheses previously proposed concerning the origin of cancer. The peculiar chromosome complex in tumor cells which shows striking differentiation from the complex in the ordinary tissue cells, together with its heritable capacity for autonomous growth, is well explicable by taking the view that the tumor cell has arisen due to a kind of mutation from the tissue cell. Probably, at some stage in the course of certain experimental treatment, a cell or a group of cells in the tissue of the normal individual undergo a mutational change in chromosomes so as to acquire a capacity for autonomous growth. Thus, the tumor cells, which possess a characteristic complex of chromosomes along with a heritable autonomous capacity and are capable of successive transmission, closely simulate a parasitic organism in their behavior.
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