It has been stated that in certain human or mammalian tumors the number of chromosomes is much decreased, even to half. It has also been stated that the number of chromosomes is greatly increased in other tumors. But the correct number of chromosomes in man has been known only during the last few years, chiefly through the accurate microscopic work of de Winiwarter and of Painter. It is now certain that there are twenty-four pairs in the human female, including two sex chromosomes, and twenty-three pairs and one sex chromosome in the human male. (Painter believed that he had found also a small Y chromosome in the male. This Y, if present, is possibly blank for purposes of inheritance.) In view of the conflicting results of previous attempts at counting the chromosomes in dividing cells of malignant and benign human tumors, chromosomal counts are being