The gist of my hypothesis (.. is) a certain abnormal chromatin constitution. Each process, which brings about this chromatin constitution, would result in the origin of a malignant tumour. Certainly, I consider irregularities with mitosis as the normal mode of the origin of an incorrectly assembled nucleus. This statement by Boveri (1914) has considered earlier observations of asymmetric divisions in human cancers (Hansemann, 1890). The hypothesis is based on the understanding of mitosis as an equational bipartition of the hereditary substance (Flemming, 1879; Roux, 1883). Latest since it was known that genes are located on chromosomes (Sturtevant, 1913), their balanced transport in anaphase appeared as a condition of correct somatic proliferation. True mitoses guarantee the constancy of terminally differentiated tissues. Politzer (1934) has performed X-ray experiments to investigate abnormal karyokinesis with regard to anomalous chromatin condensation, chromosome breakage, spindle malformation, and failure in cytokinesis. On the basis of light microscopy, further significant progress in understanding the pathology of mitosis was not possible. Tumour cases with reduced chromosome numbers seduced to the idea that mitotic activity is rather under cytoplasmic than under nuclear control (Koller, 1947).